Palestrante/Speaker: Juliano Neves (UFABC)
Resumo/Abstract:
Resumo: Não é mais colocada em dúvida a cosmologia como ciência atualmente. No entanto, uma noção de origem, dada pela singularidade inicial ou big bang, faz parte do discurso de cosmólogos no modelo padrão, algo que transcendeu os departamentos e faz parte até do discurso popular. Mas uma singularidade realmente pode ser considerada algo científico? Como uma limitação do conceito de geodésica na relatividade geral, uma singularidade pode ser apenas um conceito problemático, ou aquilo que Kant chamou de númeno. Logo, sendo um númeno não pode ser um objeto da ciência, pois esta lida com fenômenos. É o que pretendo mostrar na primeira parte do seminário. Na segunda parte, a partir da diferença kantiana entre pensar e conhecer um objeto, proponho um grau de cientificidade aplicado à cosmologia usando conjuntos fuzzy. Com isso, cosmologias sem uma origem podem potencialmente ter um grau de cientificidade maior do que aquelas com uma origem, como o modelo padrão.
Title: Measuring the ellipticity of galaxy cluster haloes using weak-lensing
Abstract: Galaxy clusters are expected to reside on highly overdense dark matter halos, which according to numerical simulations, can be well described by a triaxial model and appears elliptical in projection. In this work we constrain the average projected halo ellipticity of a sample of redMaPPer clusters (0.1 < z < 0.4) using weak-lensing stacking techniques. For the analysis we combine shear catalogs from four weak lensing surveys (KiDS/KV450, CFHTLenS, CS82, and RCSLenS). In order to estimate the major semi-axis orientation of the halos, we assume that the dark matter can be well traced by the satellite distribution. Taking this into account we compute the position angle for each redMapper cluster according to the quadrupole moments. We consider different proxies to estimate the orientation taking into account different weights for computing the quadrupole moments and a cut in the membership probability. The surface density is modelled considering a multipole expansion from which the shear components can be decomposed into the monopole and quadrupole contributions, where the quadrupole is proportional to the projected ellipticity. We derive the aligned component of the projected halo ellipticity by fitting both quadrupole component profiles, tangential and cross, within a projected distance of 100kpc < r < 5Mpc. We also study the relation between the derived projected ellipticity and the average cluster mass and redshift. Finally, we analyse the impact of misscentring in the ellipticity estimates. For the whole sample we obtain, with more than 5\sigma detection level, a median halo ellipticity of 0.17 +/- 0.03 by aligning the halos according to the distribution of all the galaxies classified as members.
Palestrante/Speaker: Tays Miranda De Andrade (UFES)
Resumo/Abstract:
Contracting cosmologies give rise to quantum vacuum fluctuations from which the primordial perturbations present in our universe could be generated. The existence of a cosmological phase before the Big Bang leads to a different perspective regarding the initial conditions for the universe. In this talk I will describe a collapsing universe, based on a scalar field and an exponential potential, and apply the stochastic formalism, which allows us to study how quantum fluctuations give rise to stochastic noise which modifies the classical dynamics of the scalar field at large scales, above a coarse-graining scale. In particular I will explore how quantum fluctuations can perturb the equation of state on large scales leading to the break down of the classical collapse solution.
Palestrante/Speaker: Nelson Pinto Neto (CBPF)
Resumo/Abstract:
Resumo: As observações cosmológicas mostram que o universo teve uma fase muito quente no passado, mas não há, até o momento, observação alguma indicando que o universo teve um começo, ou que tenha tido uma longa história anterior a esse período muito quente. Elas são perfeitamente compatíveis com um universo que era muito grande e quase vazio num passado longínquo, que tenha se contraído espacialmente até um tamanho mínimo (o ricochete), quando então efeitos físicos para além da Relatividade Geral o lançaram para a fase de expansão muito quente observada. Essa alternativa possível tem, entretanto, que responder duas questões importantes. Primeiramente, ricochetes causados por extensões clássicas da Relatividade Geral produzem, em geral, uma intensidade de ondas gravitacionais primordiais relativamente grande em relação às pequenas densidades de massa-energia primordiais que geraram as estruturas em grandes escalas do universo atual, e, portanto, são incompatíveis com as observações. Além disso, a energia escura, que hoje empurra o universo numa expansão acelerada, e que se manifesta somente em largas escalas, pode ter tido um papel importante na sua fase contrativa remota, quando o universo era espacialmente muito grande, alterando as boas previsões de uma grande classe de modelos com ricochete, que em geral não consideram seus efeitos. Neste seminário mostraremos que se o agente causador do ricochete forem modificações quânticas da Relatividade Geral, então as pequenas sementes geradoras das estruturas em largas escalas do nosso universo crescem substancialmente em relação às ondas gravitacionais primordiais nessa fase quântica, tornando a razão entre estas quantidades compatíveis com as observações. Além disso, o campo que rege a dinâmica do universo na sua fase de contração só apresenta comportamento de energia escura na fase de expansão e, portanto, não pode modificar a dinâmica contrativa compatível com as observações. Assim, a teoria quântica oferece, em uma só tacada, a solução para duas grandes questões de modelos com ricochete. Concluiremos o seminário com perspectivas futuras para esse tipo de abordagem, discutindo o “vice-versa” do título.
Quando/When: 04/11/2019, at 10:30h
Palestrante/Speaker: Gustavo E. Romero (Instituto Argentino de Radioastronomía (IAR) & Universidad Nacional de la Plata)
Resumo/Abstract:
Relativistic jets are collimated outflows from accreting compact objects. They emit radiation from radio to gamma rays and possibly neutrinos. Jets on different scales are launched by accreting binaries, quasars and other active galactic nuclei, as well as by transient sources such as gamma-ray bursts. The physics of these jets is still not well-understood. In this talk I will discuss some issues related to the origin of massive particles in relativistic jets.
Quando/When: 14/10/2019, at 10:30h
Palestrante/Speaker: Rudnei O. Ramos (UERJ)
Resumo/Abstract:
Recentemente tem havido um grande interesse na consistência de teorias efetivas no contexto de serem completas no regime ultravioleta, dentro de uma teoria de gravidade quântica/teoria de cordas. Isso tem levado a várias conjecturas, chamadas de "Swampland Conjectures". Tais conjecturas impõem severas restrições em vários modelos cosmológicos, principalmente no tocante a modelos inflacionários. É mostrado aqui como a ideia de inflação quente ("warm inflation") resolve de forma consistente tais objeções.
When: 16/09/2019, at 10:30h
Speaker: Leonardo Giani (Núcleo Cosmo-UFES and PPGCosmo)
Abstract:
An interesting class of f(R) theories that has become popular in the last years modifies the Einstein Hilbert action by adding terms containing negative powers of the d'Alembert operator. Such terms are non local by definition, and usually attributed to quantum effects. In this seminar we will show the effectiveness of some of these theories in reproducing without cosmological constant a background behavior compatible with LCDM. We will also show that these models have the same asymptotic behavior at late times, where the effective equation of state of the universe approaches the value w_{eff} -> -1.
When: 06/09/2019, at 14:30h, 3rd floor conference room (note date, time and location)
Speaker: Manoel M. Ferreira Jr. (UFMA)
Abstract:
The electron anomalous magnetic dipole moment (MDM), the gyromagnetic factor deviation from the value predicted by the pure Dirac equation due to radioactive corrections, is known with precision best than 1 part in 10¹². The electric dipole moment (EDM) of elementary particles is a tiny quantity compatible with parity-odd and time reversal-odd interactions. The EDM magnitude d, according to the Standard Model (SM) is ≈10⁻³⁸e⋅m, while the experimental measurements have reached the level ≈10⁻³¹e⋅m very recently, existing a large space for new physics to play a relevant role, beyond the Standard Model, in this scenario. The electron EDM actually provides a strong tool to constrain theoretical models that correct the electron EDM. Concerning the EDM of atoms, it holds the Schiff theorem (1963), stating that the nuclear EDM is completely screened at first order by the atom's electrons, causing no Stark spectrum shift. In this talk, we introduce some elements of the physics of MDM, EDM, Schiff theorem and Schiff moment, discussing how new Lorentz-violating theories, involving higher derivative and nonminimal couplings, can be very severely constrained by EDM and MDM experimental data.
When: 02/09/2019, at 10:30h
Palestrante: Guilherme Brando (PPGCosmo)
Resumo:
Dentro do modelo padrão de cosmologia, LambdaCDM, a atual expansão acelerada do Universo é atribuída a existência de um fluido de pressão negativa, que entra nas Equações de Einstein como uma constante cosmológica. Uma alternativa à introdução deste fluido é modificar a teoria gravitacional em escalas cosmológicas, como, por exemplo, introduzir um campo escalar capaz de reproduzir essa expansão acelerada atual. Tais teorias são chamadas Teorias Escalares Tensoriais, e neste seminário vamos focar num grupo específico destas teorias, as chamadas Teorias Efetivas de Energia Escura, que conseguem capturar, em ordem linear, um grande número de características em comum destas teorias em apenas 4 funções paramétricas dependentes do tempo. Serão apresentados como vincular e entender estas funções arbitrárias com os atuais dados cosmológicos, assim como dados de satélites e telescópios futuros.
When: 29/08/2019, at 16:00h
Speaker: Jorge Stephany Ruiz (Universidade Simón Bolívar, Caracas, Venezuela)
Note location: Auditório do 3o. andar
Abstract:
Apresentamos uma discussão elementar da energia e do momento transferidos por uma onda eletromagnética que se propaga num meio dispersivo. Nossa análise é baseada numa expressão da densidade energética do campo, válida para um meio dispersivo e na densidade do momento eletromagnético de Minkowski. Trabalhando com o modelo Drude-Lorentz construído em termos de osciladores harmônicos microscópicos amortecidos, mostramos explicitamente como a conservação da energia e o momento ocorrem neste meio dispersivo. Em particular, mostramos que o meio pode ser puxado ou empurrado quando o pulso eletromagnético entra nele, dependendo do valor da frequência.
When: 19/08/2019, at 10:30h
Speaker: Leonardo Chataignier (Institut für Theoretische Physik, Universität zu Köln, Alemanha)
Abstract:
Um dos problemas mais persistentes na cosmologia quântica canônica é o entendimento correto da dinâmica da função de onda do universo. A dificuldade está em construir uma teoria quântica unitária invariante sob reparametrizações temporais, que são análogas a transformações de calibre (gauge) em teorias de Yang-Mills. Neste seminário, vamos analisar como tal teoria pode ser construída no caso de um modelo simplificado por meio de uma analogia com teorias de calibre convencionais.
When: 05/08/2019, at 10:30h
Speaker: Maria Elidaiana da Silva Pereira (Brandeis)
Abstract:
Galaxy clusters have been established as an important tool to study the matter distribution, the formation and evolution of the structures in the Universe with great potential to be one of the most powerful cosmological probes. To achieve this, we need to understand the systematics involved in the cluster mass calibration, which is the current dominating source of uncertainties for using clusters to probe cosmology. Observationally, we can not assess the true mass of galaxy clusters, but we can rank them by some proxy for the mass. We can define a mass proxy by looking for different observables in the clusters. A good proxy should have a linear relation with the total mass of the cluster and low scatter in comparison to some observable. To meet these requirements, we proposed 𝜇⋆, a physically motivated cluster mass-proxy proportional to the total stellar mass of red and blue members, that is independent of the formation history of the red sequence and has a low scatter with the X-ray temperature relation (Palmese et al. 2019). We use redMaPPer galaxy clusters identified in the Dark Energy Survey Year 1 data for reliable calibration of 𝜇⋆ at high redshifts. In a blinded analysis, we perform the mass-calibration of 𝜇⋆ using ∼6,000 clusters in the range of 0.1 < 𝑧 < 0.65 to infer the average masses through a modelling of their stacked weak lensing signal. We use the inferred masses to estimate a jointly mass-𝜇⋆-𝑧 scaling relation. In this talk, I will present our results and discuss the use of 𝜇⋆ as a mass proxy for future applications in cluster cosmology.
When: 12/07/2019, at 16:00h (extra, note different day and time)
Speaker: Dr. Bruno Carvalho (COSMO - CBPF)
Abstract:
São estudadas e discutidas as particularidades das dinâmicas clássica e quântica de partículas com spin e sem massa - mas portadoras de carga elétrica - no âmbito da Eletrodinâmica planar. São colocadas em destaque as peculiaridades nada triviais que a presença de carga na ausência de massa pode acarretar.
When: 03/06/2019, at 10:30h
Speaker: Vivian Miranda (University of Arizona)
Abstract:
The standard paradigm of cosmology is built upon on a series of propositions on how the early, intermediate and late-time universe behaves. It predicts that the universe is currently filled with Dark Energy and Dark Matter. Understanding the properties of dark energy is plausibly the biggest challenge in theoretical physics; while we believe the general features of Dark Matter are well known. Indeed, there is a broad assumption in cosmology that the universe on its earlier stages is fully understood and that discrepancies between the standard model and current/future data are suggestive of distinct Dark Energy properties. Uncertainties on the validity of this hypothesis are rarely taken into account when forecasting surveys capabilities, even though our investigations might be severely obfuscated if the intermediate and early universe do behave abnormally. In this Colloquium, I propose a program to investigate Dark Energy and earlier aspects of our universe simultaneously with space missions in the 2020s in combination with ground-based observatories. This program will help in guiding the strategy for the future WFIRST supernova and weak lensing surveys. Besides, my investigations on how early and intermediate universe affect inferences on dark energy (and vice-versa) will support NASA on how future space missions can be used to test some of the core hypotheses of the standard model.
When: 20/05/2019, at 10:30h
Speaker: Isaia Nisoli, Departamento de Matematica, IM-UFRJ
Abstract:
In 1980, studying experimental data obtained from the Belosouv-Zabotinsky chemical reaction, Matsumoto and Tsuda introduced a model: a random dynamical system consisting of a one-dimensional unimodal map with uniform additive noise.
Through numerical simulations, varying the amplitude of the noise, Matsumoto and Tsuda conjectured that this maps presents a phenomenon they called Noise Induced Order, i.e., for small noise amplitudes the Lyapunov exponent of the stationary measure is positive and for big noise sizes the Lyapunov exponent is positive.
In this talk I will present a joint work with Galatolo and Monge, where we develop a scheme that permits us to approximate rigorously (with an explicit error bound in $L^1$) the stationary density of the system as the noise varies and use these approximations to give enclosures of the Lyapunov exponent that permit us to prove their conjecture.
When: 03/05/2019, at 16:30h
Speaker: Kirill Bronnikov (VNIIMS e Instituto de Gravitação e Cosmologia/RUDN, Moscou, Rússia)
Abstract:
The well-known problem of wormholes in general relativity (GR) is the necessity of exotic matter, violating the Weak Energy Condition (WEC), for their support. This problem looks easier if, instead of island-like configurations, one considers string-like ones, among them, cylindrically symmetric space-times with rotation. However, for cylindrical wormhole solutions a problem is the lacking asymptotic flatness, making it impossible to observe their entrances as local objects in our Universe. It was suggested to solve this problem by joining a wormhole solution to flat asymptotic regions at some surfaces $\Sigma_-$ and $\Sigma_+$ on differents sides of the throat. The configuration then consists of three regions, the internal one containing a throat and two flat external ones. We discuss different kinds of source matter suitable for describing the internal regions of such models (scalar fields, isotropic and anisotropic fluids) and present two examples where the internal matter itself and the surface matter on both junction surfaces $\Sigma_\pm$ respect the WEC. Both models are free from closed timelike curves. We thus obtain examples of regular twice asymptotically flat wormhole models in GR without exotic matter and without causality violations.
When: 29/04/2019, at 10:30h
Speaker: Cristina Furlanetto, IF-UFRGS
Abstract:
Submillimeter galaxies represent the most active sites of dusty star formation at high redshifts. They have an important role in the study of the assembly of stellar mass and the evolution of massive galaxies in the Universe. However, detailed studies of their intrinsic properties have not been possible with the early instruments due to poor spatial resolution, low sensitivity, or both. We can circumvent these difficulties by studying submillimeter galaxies that are gravitationally lensed and/or by using interferometry. In this seminar, I will present the reconstruction of the emission of strongly lensed submillimeter galaxies discovered by the Herschel Space Observatory and observed with ALMA. The results reveal the complex nature of these sources and show the power of combining strong lensing and interferometry to study star formation and the interstellar medium in the high-redshift Universe. I will also present a method for lens modelling that operates in the Fourier domain native to the interferometers.
When: 09/11/2017, at 10:30h
Speaker: Raissa Mendes, Instituto de Física - UFF
Abstract:
Scalar-tensor theories of gravity are extensions of General Relativity including an extra, non-minimally coupled scalar degree of freedom. Interestingly, a wide class of these theories, albeit indistinguishable from GR in the weak field regime, can predict a radically different phenomenology in the strong-field environment of neutron stars. In this talk, I will discuss how the presence of nonperturbative effects around highly compact neutron stars may be used to probe a variety of scalar extensions to GR.
When: 20/10/2017, at 14:00h
Speaker: María de Paz, Universidad de Sevilla
Abstract:
At the end of 18th century the discipline of mechanics was considered as a part of mathematics, usually of what was commonly known as ‘mixed mathematics’, and this included many disciplines from optics and astronomy to artillery and fortification. This status changed along the 19th century, a period in which mechanics was a part of pure mathematics, of applied mathematics and, by the end of the century of mathematical physics or even of theoretical physics, depending on the accounts. This implies the transformation of mechanics from a mathematical discipline into a physical one, or at least into a more empirically-based discipline. The aim of this talk is to understand this transformation from the point of view of the changing status of its fundamental principles and to show how this change is related to the groundbreaking changes in mathematics and in physics that took place along the century.
When: 02/10/2017, at 10:30h
Speaker: João Torres de Mello Neto, Instituto de Física - UFRJ
Abstract:
The matter that we know makes up less than 5% of the Universe. From astronomical and cosmological observations we have strong evidence that dark matter exists and is the main component of the mass budget of the universe. The nature of dark matter is yet to be discovered and is one of the most pressing questions in physics. Direct detection experiments aim to detect the interaction of galactic dark matter with terrestrial nuclei. Weekly interacting massive particles (WIMP) are a likely candidate for dark matter, but axions, hidden photons and other candidates are also considered. In this talk we will review currently available major technologies being pursued by various collaborations, with special emphasis on the CCD technology used by the DAMIC (Dark Matter in CCDs) experiment and the measurements of radioactive contamination in the CCDs.
The latest results from the experiment on the search for WIMPs interactions in the bulk silicon will be discussed. We will also present constraints on the absorption of hidden-photon dark matter. The constraints are the best direct detection limits for low mass hidden-photon dark matter. We also discuss other exotic dark matter candidates.
When: 04/9/2017, at 10:30h
Speaker: Theo M. Nieuwenhuizen, University of Amsterdam
Abstract:
Galaxy clusters were employed by Zwicky to argue for the existence of dark matter and still pose stringent tests. Modifications of Newtons law such as MOND, EG, MOG and f(R) theories are ruled out, unless $\sim 2$ eV neutrinos are added.
If dark matter is self-interacting with cross section $\sigma/m \sim 2 cm^2/gr$, MACHOs, primordial black holes and light axions are ruled out as cluster dark matter.
Recent strong lensing and X-ray gas data of the cluster A1835 allow to test thermal dark matter with classical, bosonic and fermionic distributions, next to (generalised) Navarro-Frenck-White profiles. Within the spherical approximation it is found that all these cases do not work well, except for the fermionic one. The interpretation in terms of (nearly) Dirac neutrinos with mass of $1.70^{+0.13}_{-0.17}$ eV/$c^2$ is consistent with earlier results on the cluster A1689, with the Planck and DES dark matter fractions and with the non-detection of neutrinoless double beta decay. The case will be tested in the 2018 KATRIN experiment.
When: 28/8/2017, at 10:30h
Speaker: Micol Benetti, ON
Abstract:
The currently most precise measurement of the local expansion rate H_0 by Riess et. al (2016) differs by ~ 3.4 standard deviations from the value reported by the Planck Collaboration (2015) assuming the standard cosmological model. Since the two approaches, namely using the geometric distance calibrations of Cepheids and the cosmic microwave background data, sample different epochs in cosmic evolution, and one of them uses the standard cosmological model as the fiducial cosmology, this tension in the value of H_0 has given rise to speculations. It has been argued that either new physics beyond the standard cosmology or the influence of local structures must be taken into account in order to reconcile these H_0 estimates. In this talk I introduce this H_0 tension and I present the results of our recent paper, where the effect of this discrepancy has been explored through a Bayesian analysis with the current Planck 2015 and Riess 2016 data. I present a way to alleviate such a tension studying the observational viability of the scale invariant spectrum and two of its extensions, i.e., assuming as free parameter the primordial helium mass fraction and the effective number of relativistic degrees of freedom (Neff). Also, I present analysis using Baryon Acoustic Oscillations measurements and Cluster Number counts and Weak Lensing data in order to take into account the tension on fluctuation amplitude parameter, σ8 , value which so far has always brought standard model with Neff extension to be discarded.
``Do joint CMB and HST data support a scale invariant spectrum?,'' M. Benetti, L. L. Graef and J. S. Alcaniz, JCAP 1704, no. 04, 003 (2017)
When: 31/7/2017, at 10:30h
Speaker: Leticia F. Palhares, UERJ
Abstract:
Quantum Chromodynamics is the theory that describes the interaction between quarks and gluons, the current ultimate constituents of atomic nuclei. Even though very successful, it still presents fundamental open questions. One of the most prominent is related to the mechanism of confinement, that guarantees that quarks and gluons are never observed directly and are always confined in the interior of hadrons, like protons and neutrons. In this talk, I shall present a set of theoretical models that try to explain confinement, as well as what can we learn from observation of matter under extreme conditions, in which deconfinement could take place. In particular, this physics — usually associated with microscopic phenomena — will be shown to possibly play a role in astrophysical systems involving ultra-compact objects.
When: 12/6/2017, at 10:30h
Speaker: Marc Henneaux, ULB, Belgium
Abstract:
The talk will review how asymptotic symmetries are defined and their generators constructed in theories with a gauge freedom, considering the specific case of gravity. The algebra of the conserved charges will be discussed. The analysis will be illustrated in various contexts (asymptotically anti-de Sitter spaces, asymptotically flat spaces).
When: 08/5/2017, at 10:30h
Speaker: Miguel Quartin, UFRJ
Abstract:
It is believed that the solar system is moving with a velocity of 370 km/s compared to the CMB rest frame. The main effect of this is to produce the observed CMB dipole via the Doppler effect. There are nevertheless other physical consequences of not being on the CMB rest frame which are already important at the precision level of Planck. I will discuss this and the possibilities of independently measuring this velocity and thus also the primordial CMB dipole. I will also show that not properly taking it into account leads to systematic effects, for instance on measures of some of the so-called CMB anomalies and on the overall calibration of the Planck satellite. Finally, I will talk about the prospects of measuring the velocity using future 21cm surveys.
When: 24/4/2017, at 10:30h
Speaker: Laurie Riguccini, Observatorio do Valongo/ UFRJ
Abstract:
ETGs were first believed to be read and dead but studies from the past decades have indicated that some ETGs show signs of star formation. Where does this star formation(SF) come from? Riguccini et al. (2015) unveiled a population of galaxies in transition: star-forming ETGs in the Coma cluster with a larger L24μm/LK ratio. They have shown that 70% of those star-forming ETGs are located in a the south-west part of the cluster, where a substructure is unfailing on the main cluster. In order to apply this mid-IR/near-IR selection to a wide sample of ETGs, we already checked the validity of using the WISE-all sky survey bands instead of the Sptizer-24μm/2MASS_K band ratio. We successfully found that using WISE 22μm/3.4μm is a reliable tool to select star-forming ETGs. We aim at understanding what happened in those ETGs to have a new burst of star formation and to built large samples of these objects. We aim to unveil star-forming ETGs in other clusters and explore the effect of the environment on their SF activity using the most populated clusters in the local Universe and expend it to wide survey such as the S-PLUS survey.
When: 17/4/2017, at 14:30h
Speaker: Jens Mund (UFJF)
Abstract:
Quantum field theories for interacting particles with higher spin are usually based on gauge theory. In this approach, one has to add unphysical degrees of freedom in the form of "negative norm" states and "ghost" fields before the construction, and divide them out afterwards by requiring gauge (or BRST) invariance of the S-matrix and observable fields.
In the talk an alternative approach is presented: Instead of Hilbert space positivity, the localization of the fields are weakened, in a way permitted by the principles of relativistic quantum field theory: The fields are localized on "Jordan-Mandelstam strings" extending to space-like infinity. They act in a true Hilbert space without ghosts.
The construction of interacting models is based only on the fundamental principles of unitarity, renormalizability, covariance, and locality of the observables. The latter implies a string-independence condition of the S-Matrix which has to be satisfied in every order and is quite restrictive. Any model complying with these principles must exhibit certain features -- which are thus derived from first principles. We conjecture that the following features are explained in this sense (which usually are put in by hand):
- The structure of gauge theories, namely: Lie algebra relations of the coupling constants in models with self-interacting vector bósons; minimal coupling principle; - The shape of the Higgs potential; - Chirality of electroweak interactions; and more...
Our approach also allows for a direct (perturbative) construction of charged interacting fields which interpolate between the in- and outgoing fields, which the gauge theory approach does not provide. It also provides energy-momentum tensors for massless higher helicity particles, which for point-local fields are ruled out by the Weinberg-Witten Theorem.
When: 11/4/2017, at 14:30h
Speaker: Bert Schroer (Freie Universität Berlin)
Abstract:
The short distance scale dimension d{sd}=s+1 of spin s≥1 field can be lowered to the spin-independent value of the d{sd}=1 of its string-localized counterpart. The use of such fields in a new perturbation theory permits the preservation of positivity together with renormalizability. In contrast to the positivity-violating gauge theory (for which only gauge invariant operators preserve positivity), the new setting of QFT aims at a construction of a complete QFT in which all particles are described in terms of physical fields. Among its achievements are the construction of massless currents and energy-momentum tensors (the Weinberg-Witten problem), the correct degrees of freedom counting (the van Dam-Veltman-Zakaharov discontinuity problem) and a more profound understanding of the Higgs mechanism.
When: 10/4/2017, at 14:30h
Speaker: Alessandro Codello (USD, Denmark and INFN-Bologna, Italy)
Abstract:
I'll describe the family of renormalizable scalar QFTs with self-interacting potentials of highest monomial φ^m below their upper critical dimensions dc = 2m/(m−2), and study them using a combination of CFT constraints, Schwinger-Dyson equation and the free theory behavior at the upper critical dimension.
For even integers m ≥ 4 these theories coincide with the Landau-Ginzburg description of multi-critical phenomena and interpolate with the unitary minimal models in d = 2, while for odd m the theories are non-unitary and start at m = 3 with the Lee-Yang universality class.
For all the even potentials and for the Lee-Yang universality class, I show how the assumption of conformal invariance is enough to compute the scaling dimensions of the local operators φ^k and of some families of structure constants at leading order.
Related paper: 1703.04830
When: 10/4/2017, at 10:30h
Speaker: Sergio E. Joras (UFRJ, Rio de Janeiro)
Abstract:
Modified gravity theories know as f(R) are used to generate an accelerated expansion of the universe, both in its early ages (inflation) and in more recent epochs (instead of assuming the existence of the dark energy). It is well known that any f(R) can be recast as General Relativity (GR) with an extra scalar field upon a suitable conformal transformation, i.e, in a different frame. Here we take the opposite direction: starting from GR with a scalar field, what is the corresponding f(R) in the other frame? Here we apply this procedure — know for a while [Magnano et al, 1987] — with unexpected results.
When: 27/3/2017, at 10:30h
Speaker: Omar Roldan (UFRJ, Rio de Janeiro)
Abstract:
The aberration and Doppler coupling effects of the Cosmic Microwave Background (CMB) were recently measured by the Planck satellite. The most straightforward interpretation leads to a direct detection of our peculiar velocity, consistent with the measurement of the well-known dipole. We show however, that in some cases a primordial dipolar potential can also produce such effects. But in addition it produces other signatures due to integrated terms which we will discuss in some detail. We also discuss how aberration measurements can be used to constraint some models which introduce super-horizon perturbations to explain the hemispherical asymmetry.
Related paper: 10.1088/1475-7516/2016/06/026, https://arxiv.org/abs/1603.02664
When: 13/3/2017, at 10:30h
Speaker: Thomas Durt (Aix Marseille University, France) Abstract:
Recently, non-linear modifications of the Schroedinger equation, like e.g. the Schroedinger-Newton equation have been studied in relation with the measurement problem.
In particular, the presence of a non-linearity would explain why the wave packet associated to a quantum particle does not spread with time. In other words, particles behave as solitons, which is strongly reminiscent of de Broglie's Double Solution Program, elaborated by Louis de Broglie in the twenties, of which the de Broglie-Bohm pilot wave dynamics is a simplified version. It is also reminiscent of Poincare's pressure, invoked by Poincare in 1905 in order to solve the wave-particle duality in the context of classical field theory. We shall describe recent attempts to derive the de Broglie-Bohm pilot wave dynamics from non-linear wave dynamics, and to apply them to quantum corpuscles at one side, and to so-called bouncing oil droplets at the other side.
Related papers:
http://iopscience.iop.org/article/10.1209/0295-5075/114/10004/meta Thomas Durt, Generalized guidance equation for peaked quantum solitons and effective gravity, EPL (Europhysics Letters), Volume 114, Number 1.
https://arxiv.org/abs/1602.03133 Thomas Durt, Generalized guidance equation for peaked quantum solitons: the single particle case.
When: 20/2/2017 at 10:30h
Speaker: James Unwin (University of Illinois at Chicago, U.S.A.)
Abstract:
Cold dark matter provides a remarkably good description of cosmology and astrophysics. However, observations connected with small scales might be in tension with this framework. In particular, structure formation simulations suggest that the density profiles of dwarf spheroidal galaxies should exhibit cusps, in contrast to observations. I will show that Fermi repulsion can explain the observed cored density profiles in dwarf galaxies for sub-keV fermionic dark matter. While in conventional dark matter scenarios, such sub-keV thermal dark matter would be excluded by free streaming bounds, I will argue that these constraints are ameliorated in models with dark matter at lower temperature than conventional thermal scenarios. Finally, I will outline a class in which the dark matter typically has a lower temperature than the thermal expectation, dubbed Flooded Dark Matter, and discuss aspects of model building.
When: 5/12/2016 at 10:30h
Speaker: Vicente Antunes (CBPF)
Abstract:
Uma das questões cruciais na cosmologia moderna está relacionada à observação da assimetria de barions no universo. Nos modelos usuais de bariogênese a gravitação desempenha papel secundário, embora o processo tenha muito provavelmente ocorrido nos primórdios da atual fase de expansão do universo onde o campo gravitacional era extremamente forte. Nesse trabalho reexaminamos a proposta original de Sakharov no qual a gravitação está no centro da bariogênese. Veremos que dependendo do modo como a matéria se acopla com a gravitação ela pode implicar na não conservação do número bariônico e concomitantemente à violação de CP. Ademais, acoplamento não-mínimo com a gravitação é capaz de induzir massa efetiva reduzida dos quarks favorecendo transição de fase na QCD. Como consequência, uma eficiente assimetria bariônica ocorre na transição da época dos quarks para a época hadrônica. Quando quarks e gluons se tornam confinados o presente mecanismo evanesce e a assimetria se congela.
One of the biggest puzzles in modern cosmology is the observed baryon asymmetry in the universe. In current models of baryogenesis gravity plays a secondary role, although the process is believed to have happened in the early universe, under the influence of an intense gravitational field. In the present work we resume Sakharov's original program for baryogenesis and propose a central role for gravity in the process. This is achieved through a non-minimal coupling (NMC) between the gravitational field and both the strong interaction field and the quark fields. When in action, the present mechanism leads to baryon number non-conservation and CP violation. Moreover, the NMC induces reduced effective quark masses, which favours a first order QCD phase transition. As a consequence, a baryon asymmetry can be attained in the transition from the quark epoch to the hadron epoch.
When: 18/11/2016 at 10h30
Speaker: Leila Graef (Observatório Nacional, Rio de Janeiro)
Abstract:
Standard inflationary models yield a characteristic signature of a primordial power spectrum with a red tensor and scalar tilt. Nevertheless, it was recently suggested that, by breaking the assumption of spatial diffeomorphism invariance in the context of the effective field theory of inflation, a blue tensor spectrum can be achieved without violating the Null Energy Condition. In this context, we explore in which cases a blue tensor tilt can be obtained along with a red tilt in the scalar spectrum. Ultimately, we analyze under which conditions this model can reproduce the specific consistency relation of String Gas Cosmology.
Related paper: arXiv: 1506.00896v1 [astro-ph.CO] (JCAP v. 2015, p. 009-009, 2015); http://iopscience.iop.org/article/10.1088/1475-7516/2015/10/009/pdf
When: 3/11/2016 at 14h
Speaker: Deirdre Shoemaker (Georgia Institute of Technology, U.S.A.)
Abstract:
For decades, both the gravitational wave and numerical relativity communities have worked to prepare for the era of gravitational wave astronomy. With the first observation of two black holes merging (GW150914), quickly followed by a second (GW151226), the new era of gravitational wave astronomy has begun. I will present the role that numerical relativity played in the unveiling of the gravitational wave sky and anticipate how it might improve our understanding of astrophysics.
When: 10/10/2016 at 10h30
Speaker: Gustavo Pazzini de Brito (CBPF)
Abstract:
In this talk we introduce a modified covariant quantum algebra based in the so-called Quesne-Tkachuk algebra. By means of a deformation procedure we arrive at a class of higher derivative models of gravity. The study of the particle spectra of these models reveals an equivalence with the physical content of the well-known renormalizable and super-renormalizable higher derivative gravities. The particle spectrum exhibits the presence of spurious complex ghosts and, in light of this problem, we suggest an interesting interpretation in the context of minimal length theories. Also, a discussion regarding the non-relativistic potential energy is proposed.
Related paper: https://arxiv.org/abs/1610.01480
When: 10/10/2016 at 10h30
Speaker: Niels Warburton (Massachusetts Institute of Technology, U.S.A., and University College Dublin, Ireland)
Abstract:
Gravitational waves have opened a new window on our Universe. Just over a year ago we did not know that black holes exist in binaries; that the components of such binaries could be very heavy, implying interesting astrophysics in the environment in which the black holes formed; and nor had Einstein's theory of General Relativity ever been tested in the highly dynamical, strong-field regime. These insights and more were gleaned from just two signals that each lasted less than a second and contained a few tens of GW cycles. Imagine what we will learn about the dark side of the cosmos from signals that last minutes or even years?
The gravitational waves from the inspiral of a stellar-mass compact object into a larger black hole will provide such long lasting signals. In this talk I will briefly review the recent detection of gravitational waves before discussing how black hole perturbation theory can be used to model small mass-ratio binaries. I will concentrate on rapidly rotating black holes, the subject of work we recently published in Classical and Quantum Gravity.
Related papers: http://iopscience.iop.org/article/10.1088/0264-9381/33/15/155002/meta or arXiv: http://arxiv.org/abs/1603.01221
Speaker's website: nielswarburton.net
NOTE: The seminar will be broadcast on the weblink https://hangouts.google.com/hangouts/_/ucd.ie/seminardrnwarburton It is via Google Hangouts, so if you connect, please make sure to turn off your microphone sound and camera so that we do not hear you in the seminar room.
When: 14/04/2016 at 10h30
Speaker: Luciano Casarini (Visiting Professor at UFES, Vitoria)
Abstract:
We discuss an extension of the Coyote emulator to predict non-linear matter power spectra of dark energy models with a scale factor dependent equation of state of the form w = w_0 + ( 1 - a )w_a . The extension is based on the mapping rule between non-linear spectra of DE models with constant equation of state and those with time varying one.
http://www.cosmo-ufes.org/luciano-casarini.html
When: 07/04/2016 at 10h30
Speaker: Hermano Velten (CPT, Marseille and UFES, Vitoria)
Abstract:
By using observations of the Hulse-Taylor pulsar we constrain the gravitational wave (GW) speed to the level of 10−2. We apply this result to scalar-tensor theories that generalize Galileon 4 and 5 models, which display anomalous propagation speed and coupling to matter for GWs. We argue that this effect survives conventional screening due to the persistence of a scalar field gradient inside virialized overdensities, which effectively "pierces" the Vainshtein screening. In specific branches of solutions, our result allows to directly constrain the cosmological couplings in the effective field theory of dark energy formalism.
http://arxiv.org/abs/1507.05047
When: 24/02/2016 at 10h30
Speaker: Martin Landriau (The University of Texas - Mc Donald Observatory)
Abstract:
After reviewing the basics of cosmic string formation and evolution, I will describe the cosmological consequences of their formation, focusing on their effects on the cosmic microwave background and presenting some new results. I will conclude by discussing future prospects for detection in the light of current observational constraints.
Martin's webpage http://www.as.utexas.edu/~landriau/Site/Home.html
When: 02/12/2015 at 10h30
Speaker: Aleksey Toporensky (Lomonosov Moscow State University)
Abstract:
A Universe filled with a homogeneous scalar field exhibits `Cosmological hysteresis'. Cosmological hysteresis is caused by the asymmetry in the equation of state during expansion and contraction. This asymmetry results in the formation of a hysteresis loop whose value can be non-vanishing during each oscillatory cycle. For flat potentials, a negative value of the hysteresis loop leads to the increase in amplitude of consecutive cycles and to a universe with older and larger successive cycles. Such a universe appears to possess an arrow of time even though entropy production is absent and all of the equations respect time-reversal symmetry ! Cosmological hysteresis appears to be widespread and exists for a large class of scalar field potentials and mechanisms for making the universe bounce.
When: 21/10/2015 at 10h30
Speaker: Przemyslaw Malkiewicz (APC - Paris)
Abstract:
Dynamics of general relativistic systems is given with respect to internal clocks. I investigate the extent to which the choice of internal clock in quantum description of the gravitational field determines its quantum dynamics. Within a fixed quantization I find the abundance of possible semiclassical extensions to general relativity just by switching between clocks. It follows that quantities like minimal volume, maximal curvature and even a number of quantum bounces, often used to describe quantum effects in gravity, are not well-defined.
When: 14/10/2015 at 10h30
Speaker: Samuel Colin (New Postdoc at ICRA CBPF)
Abstract:
According to inflationary cosmology, the cosmic structure, in particular that of the cosmic microwave background, is seeded by the primordial vacuum fluctuations of the inflation field. Recent results reported by the Planck Team suggest that there is an anomalous large-scale power deficit in the cosmic microwave background. During this talk, I will show that such a deficit occurs naturally in the de Broglie Bohm pilot-wave theory, which is a deterministic formulation of quantum theory in which the Born law arises dynamically (a process referred to as relaxation to quantum equilibrium), provided that the inflation field is initially in a state of quantum non-equilibrium (the Born law is not satisfied). More specifically, for a radiation-dominated pre-inflationary era, the deficit will have a characteristic shape (an inverse-tangent dependence on k, the wave-number, with oscillations), which is compatible with the observed data for an appropriate choice of cosmological parameters.
This talk is based on recent works done in collaboration with Antony Valentini (Clemson University):
http://arxiv.org/abs/1306.1579 and http://arxiv.org/abs/1407.8262.
When: 24/09/2015 at 10h30
Speaker: Salvatore Capozziello (University of Naples "Federico II", Italy)
Abstract:
We discuss the metric and metric-affine theories of gravity in
view of addressing open problems like dark energy and dark matter in
cosmology. In particular we discuss geodesic and metric structures with
the aim to identify the fundamental variables capable of describing the
gravitational field. The role of Equivalence Principle is considered. Some
experimental proposals are reviewed.
http://www.researchgate.net/profile/Salvatore_Capozziello
When: 16/09/2015 at 10h30
Speaker: Camila Novaes (ON - Rio de Janeiro)
Abstract:
We use Minkowski Functionals to explore the presence of non-Gaussian signatures in simulated cosmic microwave background (CMB) maps. Precisely, we analyse the non-Gaussianities produced from the angular power spectra emerging from a class of inflationary models with a primordial step- like potential. This class of models are able to perform the best-fit of the low-l ‘features’, revealed first in the CMB angular power spectrum by the WMAP experiment and then confirmed by the Planck collaboration maps. Indeed, such models generate oscillatory features in the primordial power spectrum of scalar perturbations, that are then imprinted in the large scales of the CMB field. Interestingly, we discover Gaussian deviations in the CMB maps simulated from the power spectra produced by these models, as compared with Gaussian ΛCDM maps. Moreover, we also show that the kind and level of the non-Gaussianities produced in these simulated CMB maps are compatible with that found in the four foreground-cleaned Planck maps. Our results indicate that inflationary models with a step-like potential are not only able to improve the best-fit respect to the ΛCDM model accounting well for the ‘features’ observed in the CMB angular power spectrum, but also suggesting a possible origin for certain non-Gaussian signatures observed in the Planck data.
When: 19/08/2015 at 10h30
Speaker: Niels Warburton (MIT)
Abstract:
In this talk I shall review progress using black hole perturbation theory techniques to understand the two-body problem in the general relativistic context. There is mounting evidence that techniques originally envisioned to be solely applicable to modeling sources for space-based gravitational-wave detectors will find utility across a wide range of mass ratios. I will concentrate on the self-force approach whereby the inspiral of a compact object into a massive black hole is computed by calculating the local `self-force’ that the particle experiences due to its interaction with its own metric perturbation. I will discuss a number of recent results and future research directions being taken by the self-force community.
When: 22/07/2015 at 10h30
Speaker: Fulvio Sbisa (University of Portsmooth)
Abstract:
The discovery of the late time accelerated expansion of the universe remains puzzling fifteen years after its discovery. Despite the acceleration may be due to vacuum energy or to a "dark" source of energy, it may be that the observations are just signalling a breakdown of the validity of GR on very large scales. I will present a model based on the braneworld paradigm, the Cascading DGP model, which aims to provide a consistent modification of General Relativity on ultra large distances, and may shed light on the cosmological acceleration and the cosmological constant problems. I will in particular discuss the presence/absence of a ghost instability depending on the amount of vacuum energy present in our 4D world.
When: 17/06/2015 at 10h30
Speaker: Leandro Beraldo e Silva (IF, USP)
Abstract:
A determinação do estado de equilíbrio (perfil de densidades e distribuição de velocidades) de sistemas auto-gravitantes como aglomerados globulares, galáxias e halos de matéria escura é um problema antigo e ainda sem solução completa. Nos últimos anos, simulações numéricas têm fornecido informações importantes sobre estas funções, mas sua explicação nos termos da mecânica estatística ainda não foi satisfatoriamente dada, embora algumas propostas teóricas tenham sido formuladas recentemente. Nesteseminário, introduziremos este problema e discutiremos testes observacionais de diferentes modelos (fenomenológicos e teóricos) para os perfis de densidade, utilizando dados de aglomerados de galáxias obtidos via lentes gravitacionais. Ao fim, apresentaremos um modelo teórico proposto por nós (em que o conceito de indistinguibilidade é associado ao nível de mistura do sistema), mostrando as implicações para o perfil de densidades e como esta associação levanta dúvidas sobre a validade da equação de Vlasov durante o processo de colapso dos halos de matéria escura.
When: 27/04/2015 at 10h30
Speaker: Dr. Alessandro Fabbri, Centro Fermi and Univ. Bologna (Italy), IFIC-CSIC, Univ. Valencia (Spain)
Abstract:
The Hawking effect (quantum particle creation by black holes) is not specific to gravity. An analog of it can be found in fluids undergoing supersonic flow (called acoustic black holes). We review ongoing attempts to observe it in condensed matter systems, and focus on a proposal to detect it through correlation measurements in Bose-Einstein condensates.
http://arxiv.org/pdf/1411.7842.pdf
Suggestions for 2019:
Old List [check which speakers were actually invited]:
I | Attachment | Action | Size | Date | Who | Comment |
---|---|---|---|---|---|---|
Warburton_Rio2.pdf | manage | 5987.2 K | 2016-10-10 - 04:18 | MarcCasals | Dr. N. Warburton - seminar slides | |
FASER_CBPF.pdf | manage | 47915.6 K | 2019-12-13 - 03:20 | MartinMakler | FASER: Felix Kling talk on Dec. 17, 2018 |