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Title: Loop Quantum Cosmology and the Cosmic Microwave Background. Speaker: Iván Agulló (Louisiana State University, USA) Abstract: Loop quantum cosmology has become a robust framework to describe the highest curvature regime of the early universe. In this theory, inflation is preceded by a bounce replacing the big bang singularity. I will summarize the theoretical framework, and explore the corrections to the inflationary predictions for the primordial spectrum of cosmological perturbations that this pre-inflationary, quantum gravity phase of the universe introduces. The impact of the bounce on non-Gaussianity and the exciting relation to the observed large scale anomalies in the CMB will be discussed. |
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Title: Entropy budget in black hole evaporation. Speaker: Ana Alonso-Serrano (Institute of Theoretical Physics, Charles University, Prague) Abstract: Blackbody radiation contains (on average) an entropy of 3.9+-2.5 bits per photon. The flip side of this observation is the information budget: If the emission process is unitary, as it certainly is for normal physical burning, then this entropy is exactly compensated by the “hidden information” in the correlations. We shall now extend this argument to the Hawking radiation from black holes, demonstrating that the assumption of unitarity leads to a perfectly reasonable entropy/information budget. In order to carry out this calculation we adopt a variant of the “average subsystem” approach, but consider a tripartite pure system that includes the influence of the rest of the universe. |
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Title: Dark photon searches with atomic transitions. Speaker: Clara Álvarez Luna (Universidad Complutense de Madrid) Abstract: Dark matter could be made up of dark photons, massive but very light particles whose interactions with matter resemble those of usual photons but suppressed by a small mixing parameter X. We analyze the main approaches to dark photon interactions and how they can be applied to direct detection experiments which test different ranges of masses and mixings. The most important experiments are revised, focusing on the constraints they have found or are expected for the parameter space of the theory. A new experiment based on counting dark photons from induced atomic transitions in a target material is proposed. This aproach appears to be the most appropiate one for dark photon detection in the meV mass range, extending the constraints in the mixing parameter by up to 8 orders of magnitude with respect to previous experiments. |
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Title: Cosmological Backreaction: review and toy models . Speaker: Ismael Ayuso (Instituto de Astrofísica e Ciências do Espaço) Abstract: Due to the non-commutation of spatial averaging and temporal evolution, inhomogeneities and anisotropies (cosmic structures) influence the evolution of the averaged Universe via the cosmological backreaction mechanism. In addition, cosmological backreaction has been shown to be relevant for observational (precision) cosmology and it could provide a mechanism to reproduce the current acceleration of the Universe. I will study a toy model which is called “egg-box model” to obtain an effective Cosmological Constant which appears with the emergence of structures. However, to reproduce the observations, the free parameters of this model must be fitted in agreement with the size of structures. |
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Title: Screening three-form fields. Speaker: Tiago Barreiro (Instituto de Astrofísica e Ciências do Espaço) Abstract: We consider possible screening mechanisms for a three-form field conformally coupled to matter. Through spontaneous symmetry breaking the field can acquire a non-zero vev around high densities. We show how the three-form field profile around a massive body compares with a vector field and impose limits on the theory parameters from current observational bounds. |
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Title: Coupled Quintessence. Speaker: Bruno Barros (Instituto de Astrofísica e Ciências do Espaço) Abstract: I will present a model of dark energy driven by a single canonical scalar field coupled to two cold dark matter components. I will show a background solution and dive into perturbation theory. I will also give a brief introduction to a model of coupled non-canonical quintessence. |
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Title: Initial conditions for inflation: the role of fluctuation-dissipation dynamics. Speaker: Mar Bastero Gil (University of Granada) Abstract: We study the problem of initial conditions for slow-roll inflation along a plateau-like scalar potential within the framework of fluctuation-dissipation dynamics. We consider, in particular, that inflation was preceded by a radiation-dominated epoch where the inflaton is coupled to light degrees of freedom and may reach a near-equilibrium state. We show that the homogeneous field component can be sufficiently localized at the origin to trigger a period of slow-roll if the interactions between the inflaton and the thermal degrees of freedom are sufficiently strong and argue that this does not necessarily spoil the flatness of the potential at the quantum level. We further conclude that the inflaton can still be held at the origin after its potential begins to dominate the energy balance, leading to a period of thermal inflation. This then suppresses the effects of nonlinear interactions between the homogeneous and inhomogeneous field modes that could prevent the former from entering a slow-roll regime. Finally, we discuss the possibility of an early period of chaotic inflation, at large field values, followed by a first stage of reheating and subsequently by a second inflationary epoch along the plateau about the origin. This scenario could prevent an early overclosure of the Universe, at the same time yielding a low tensor-to-scalar ratio in agreement with observations. |
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Title: Theoretical aspects of Born-Infeld theories of gravity with applications to cosmology. Speaker: José Beltrán Jiménez (CPT, Aix Marseille Université) Abstract: In order to regularize the energy of point-like charged particles, Born and Infeld introduced a modification of the Maxwell Lagrangian that naturally imposes an upper bound on electromagnetic fields. Similar ideas can be applied to gravity to resolve the GR singularities. I will discuss a class of theories based on this scheme and present a scenario where inflation can be supported by a dust component. |
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Title: The growth rate in phantom dark energy models. Speaker: Mariam Bouhmadi-López (UPV/IKERBASQUE) Abstract: We carry out an analysis of the cosmological perturbations in general relativity for three different models which are good candidates to describe the current acceleration of the Universe. These three set-ups are described classically by perfect fluids with a phantom nature and represent deviations from the most widely accepted ΛCDM model. In addition, each of the models under study induce different future singularities or abrupt events known as (i) Big Rip, (ii) Little Rip and (iii) Little Sibling of the Big Rip. Only the first can be regarded as a true singularity. For this reason, we refer to the others as abrupt events. With the aim to find possible footprints of this scenario in the Universe matter distribution, we not only obtain the evolution of the cosmological scalar perturbations but also calculate the matter power spectrum for each model. Finally, we compare the predictions of these models with current observational data corresponding to the growth rate function, more precisely fσ8 reaching the conclusions that these models are fully consistent with observations. |
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Title: Electrodynamics and spacetime geometry - Foundations and Applications. Speaker: Francisco Cabral (Faculty of Sciences, Institute of Astrophysics and Spce Sciences) Abstract: After a brief overlook into the foundations of electromagnetism in the (pre-metric) formalism using exterior calculus, we explore some astrophysical applications of the coupling between electromagnetism and gravity. We consider electrodynamics on curved spacetime and address different possible physical effects resulting form the coupling with gravity, such as additional electromagnetic couplings in the Gauss and Maxwell-Ampère laws as well as gravitomagnetic effects. We will give a special relevance to the applications to gravity waves (GW). The coupling between electric and magnetic fields to gravity opens important windows to deepen the study of the physics of GW sources and GW detectors. We will analyse electric and magnetic fluctuations induced by GW and the possibility of measuring these effects using very sensitive magnetometers such as SQUIDS (Superconducting Quantum Interference Devices) and resonant cavities. |
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Title: Varying speed of light cosmologies. Speaker: Mariusz Dabrowski (University of Szczecin) Abstract: During my talk I will discuss a couple of theoretical formulations of varying c theories as alternative gravity theories and discuss their benefits as well as problems. I will review some cosmological tests of VSL theories making also a comparative statistical analysis of the basic theoretical frameworks. |
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Title: CMB bounds on the field content of the Universe.. Speaker: Adrián del Río (Depto. Física Teórica & IFIC - UV & CSIC) Abstract: Spectator (free) fields present during single-field inflation can affect CMB observables through quantum effects. They renormalize background quantities and induce logarithmic running in correlation functions of curvature perturbations. They also generate non-Gaussianities. In this talk we consider the effect of a large number of such degrees of freedom on inflationary observables, and show that one can extract bounds on the hidden field content of the universe through bounds on the running of the CMB spectral indices. We shall discuss implications for various phenomenological scenarios and generalizations. |
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Title: Observable traces of non-metricity: accelerator constraints on metric-affine gravity. Speaker: Adrià Delhom (Depto. Física Teórica & IFIC - UV & CSIC) Abstract: Non-metricity is a geometric property that plays an important role in metric-affine theories of gravity but which has received little attention in applications involving fermionic fields. In this talk, I will introduce the Dirac Lagrangian that must be used in a non-Riemannian background and will then show that contact 4-fermion interactions arise setting a lower energy scale in which Born-Infeld inspired theories of gravity are compatible with accelerator experiments. |
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Title: Local density of relic neutrinos with minimal mass. Speaker: Pablo Fernández de Salas (Depto. Física Teórica & IFIC - UV&CSIC) Abstract:Neutrino oscillations have shown that these weakly interacting particles have a mass different from zero, although cosmology points towards smaller values for their masses than previously expected. Despite the smallness of their mass, relic neutrinos coming from the time of their decoupling might cluster under strong gravitational potentials, such as the one of our galaxy, leading to an overdensity of such neutrinos in our surroundings. This can be helpful for future experiments' aiming at detecting relic neutrinos, like PTOLEMY. I will discuss an update on the gravitational clustering of relic neutrinos in the Milky Way, showing that the expected overdensity is unfortunately lower than desired. |
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Title: Adiabatic regularization with a Yukawa interaction. Speaker: Antonio Ferreiro (Depto. Física Teórica & IFIC - UV&CSIC) Abstract:We extend the adiabatic regularization method for an expanding universe to include the Yukawa interaction between quantized Dirac fermions and a homogeneous background scalar field. We give explicit expressions for the renormalized expectation values of the stress-energy tensor and the bilinear $\langle \bar\psi\psi\rangle$ in a spatially flat FLRW spacetime. These are basic ingredients in the semiclassical field equations of fermionic matter in curved spacetime interacting with a background scalar field. The ultraviolet subtracting terms of the adiabatic regularization can be naturally interpreted as coming from appropriate counterterms of the background fields. We fix the required covariant counterterms. To test our approach we determine the contribution of the Yukawa interaction to the conformal anomaly in the massless limit and show its consistency with the heat kernel method using the effective action. |
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Title: Gravitational waves as a probe of the early Universe. Speaker: Daniel G. Figueroa (CERN) Abstract: I will present a survey of the gravitational wave backgrounds expected from the early Universe, and discuss our experimental ability to constrain the physics (beyond the Standard Model) responsible for them. |
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Title: Gravitational waves from primordial black holes as dark matter. Speaker: Juan García-Bellido (IFT-UAM/CSIC) Abstract: TBA |
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Title: Weak lensing magnification: a probe for the Dark Universe. Speaker: Manuel García-Fernández (CIEMAT) Abstract: During the last years, extensive wide field imaging surveys have allowed the measurement of weak gravitational lensing effects focusing on the shape-distortion statistics: shear-shear or galaxy-shear correlations. Nevertheless, the other half of signal: the change on the observed luminosity of galaxies --that is, magnification-- has been little studied due to its lower signal-to-noise ratio. Recent developments on new systematic analysis techniques open a new way to measure magnification allowing to use it as a complementary probe for Cosmology, namely Dark Matter and Dark Energy. |
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Title: Modified Gravity. Speaker: Lavinia Heisenberg (Institute for Theoretical Studies, ETH Zurich, Switzerland) Abstract: I will discuss different attempts to modify the gravitational interactions in the UV and IR together with their underlying motivations. Among the UV modifications I will pay special attention to the Born-Infeld inspired gravity theories and explain their dominant features. For the IR modifications on the other hand, I will discuss the developments and progress made in massive gravity, scalar-tensor and vector-tensor theories and emphasise their common and distinctive features. |
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Title: Observational effects of varying speed of light in quadratic gravity cosmological models. Speaker: Azam Izadi (K. N. Toosi University of technology, Tehran, Iran.) Abstract: We study different manifestations of the speed of light in theories of gravity where metric and connection are regarded as independent fields. We find that for a generic gravity theory in a frame with locally vanishing affine connection, the usual degeneracy between different manifestations of the speed of light is broken. In particular, the space--time causal structure constant ($c_{ST}$) may become variable in that local frame. For theories of the form $f(R,R^{\mu\nu} R_{\mu\nu})$, this variation in $c_{ST}$ has an impact on the definition of the luminosity distance (and distance modulus), which can be used to confront the predictions of particular models against Supernovae type Ia (SN Ia) data. We carry out this test for a quadratic gravity model without cosmological constant assuming i) a constant speed of light and ii) a varying speed of light, and find that the latter scenario is favored by the data. |
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Title: Data constraints on viable classes of f(R) gravity. Speaker: Sulona Kandhai (University of Cape Town) Abstract: A viable model for f(R) gravity, especially in the context of the late time acceleration observed, is investigated. One of the biggest challenges faced in this field is the handling of the appearance of sudden cosmological singularities in the evolution of most viable f(R) models. This problem is looked at in an scalar tensor representation, and then a numerical view of the parameter space of the Hu-Sawicki model is discussed, showing regions of the parameter space which are singularity free. Background data constraints, coming from SNIa, on the free parameters of the Hu-Sawicki model is then presented. |
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Title: The ISW imprint of Supervoids: from simulations to DES, BOSS and Euclid data. Speaker: Andras Kovacs (IFAE Barcelona) Abstract: The integrated Sachs-Wolfe imprint of extreme structures in the cosmic web probes the dynamical nature of dark energy. Looking through typical cosmic voids, no anomalous signal has been reported. On the contrary, supervoids, associated with large-scale fluctuations in the gravitational potential, have shown potentially disturbing excess signals in WMAP and Planck CMB temperature data. In this talk, I summarize the status of localized measurements of this tiny imprint. Focusing on the Jubilee ISW simulation, I demonstrate how the stacked signal depends on void properties. Foremost, a peculiar ISW imprint shape with central cold spots and surrounding hot rings is observable for the largest voids. Interestingly, the stacking analyses of real-world BOSS and DES void catalogues reveal a strongly enhanced ISW(-like) imprint at these large scales, unlike previous studies that used different void definitions and reported good consistency with LCDM estimates. Some features, including differences in the shape of the imprints and sensitivity to void center definitions points to the fragility of the excess signal. However, a very similar excess signal is seen both BOSS and DES data for the largest voids thus we might see a new phenomenon or a hitherto undiscovered systematic effect that is correlated with large-scale density modes without dependence on CMB frequency. Finally, I show that such a very large enhancement of the ISW amplitude parameter hints at a possible causal relation between the CMB Cold Spot and the Eridanus supervoid. The origin of these findings remains unclear, but certainly warrants further studies with more data from large galaxy surveys including Euclid. |
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Title: Interuniversal entanglement in cyclic multiverse models. Speaker: Manuel Krämer (University of Szczecin) Abstract: We study models of a multiverse consisting of parallel cyclic universes that are classically disconnected, but quantum-mechanically entangled. These models are based on a quantum field theoretical formulation of the Wheeler-DeWitt equation, the so-called third quantization. We investigate models with sinusoidal cycles starting with a big bang and ending with a big-crunch singularity as well as models with tangential cycles going from a big bang to a big rip. For the sinusoidal model, we find that the entropy and temperature of entanglement are large at the big bang and big crunch as well as at the maximum of expansion of the parallel universes. This hints towards a relation to earlier findings that quantum effects are strong at the turning points of the evolution of a universe. For the tangential model, however, the entropy of entanglement is going to zero at the big-rip singularities, whereas the temperature is again large. |
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Title: Non-local $R^2$ inflation and Quantum gravity. Speaker: Sravan Kumar (University of Beira Interior, Covilhã, Portugal ) Abstract: In this talk, I aim to convince that the analytic infinite derivative (AID) non-local extension of $R^2$ gravity is the most general theory of gravity can be written around Maximally symmetric space times. It can be supported that this theory is inspired String field theory and is ghost free and renormalizable. I will discuss about inflationary solutions in this model and compare it with Starobinsky model (local $R^2$ gravity). I will present some of the observational predictions of this model as a viable target for future CMB data. |
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Title: CANTATA: a modified gravity European project. Speaker: Ruth Lazkoz (University of the Basque Country - UPV/EHU) Abstract: An overview of the CANTATA COST action. |
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Title: Analysing a forecast cosmological redshift drift. Speaker: Iker Leanizbarrutia (University of Basque Country - UPV/EHU) Abstract: We create a model independent mock dataset to test the viability and possible properties of the cosmological redshift drift, or Sandage-Loeb (SL) test. We also use future mock datasets of Supernovae Ia (SN) and Baryon Acoustic scillation (BAO) to compare with SL, and also to see its performance when using all datasets. The behaviour of datasets are analysed through testing several cosmological models with MCMC. SL dataset presents in general a remarkable constrains on $\Omega_{m}$ parameter on every tested model, showing also different correlations with dark energy parameters comparing to SN and BAO data. |
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Title: Preparing ESPRESSO's fundamental physics tests. Speaker: Ana Catarina Leite (Instituto de Astrofísica e Ciências do Espaço) Abstract: ESPRESSO is a high-resolution-ultra-stable spectrograph for the VLT, whose commissioning will start this year. One of its key science goals is to test the stability of nature's fundamental couplings with unprecedented accuracy and control of possible systematics. As the first light approaches quickly a set of ESPRESSO-like spectra is beeing simulated to evaluate the optimal strategy to detect a possible variation of fine-structure constantlooking into metal absorption lines produced by the intervening clouds along the line of sight of the QSO. In this talk, I will present the ongoing spectra simulations and show examples of the complexity of the observational features that are key to improved measurements of the variation of the fine structure constant using ESPRESSO. I will also discuss the impact that these improved measurements can have on cosmology, more specifically on Bekenstein-type models. |
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Title: Wormholes, warp drives and energy conditions. Speaker: Francisco S.N. Lobo (Instituto de Astrofísica e Ciências do Espaço) Abstract: We consider the possibility of wormhole spacetimes, ranging from the Einstein-Rosen bridge, geons, and the modern renaissance of these space-time tunnels. A fundamental property in wormhole physics is the flaring-out condition of the throat, which through the Einstein field equation entails the violation of the null energy condition. In the context of modified theories of gravity, it has recently been shown that the matter threading the wormhole can be imposed to satisfy the energy conditions, and it is the higher order curvature terms, interpreted as a gravitational fluid, that sustain these non-standard wormhole geometries, fundamentally different from their counterparts in general relativity. In addition to exploring interesting features of these geometries, in particular, the physical properties and characteristics of these ‘exotic spacetimes’, we also analyze other non-trivial general relativistic geometries, such as warp drive geometries, that generate closed timelike curves. |
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Title: Varying couplings and dark energy: a meta-analysis. Speaker: Carlos Martins (IA, Porto) Abstract: Astrophysical tests of the stability of fundamental couplings are becoming an increasingly important probe of new physics. Motivated by the recent availability of new and stronger constraints we have carried out a statistical meta-analysis of all currently available measurements of the fine-structure constant, the proton-to-electron mass ratio and the proton gyromagnetic ratio (as well as combinations thereof), allowing for both time and/or spatial variations. I will summarize these results and also discuss how, in combination with local tests with atomic clocks, they strongly constrain fundamental physics scenarios including dynamical dark energy. |
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Title: Dark matter searches with KAT-7, Meer-KAT and SKA telescopes. Speaker: Miguel Méndez Isla (University of Cape Town) Abstract: We study the possibility of dark matter detection using the Square Kilometer Array (SKA) radio telescope by electron-positron emission. We shall present how to fit the fluxes data to analytic functions in order to determine the integrated fluxes. After modeling the technicalities of the SKA detectors, constraints on viable models of dark matter can be set up. We shall show how the analysis of the results remains, for instance, essential in order to determine the absence or importance of the astrophysical boost factor, the branching ratios of annihilations for dark matter particles, the compatibility of the SKA results with direct and indirect methods and finally, the number of dark matter candidates required to explain the results. |
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Title: Exploring the stability of thermal equilibrium between matter and horizon . Speaker: José Pedro Mimoso (FCUL, Lisboa) Abstract: The assumption that the temperature of the fluids inside the cosmic horizon (including dark energy) coincides with the temperature of the latter is usually adopted in the thermodynamic analysis of homogeneous and isotropic cosmological models. However as the temperatures of the matter or radiation components evolve under different time-temperature laws, it is important to examine up to what extent the equilibrium assumption may be justified. We argue here that while for the radiation dominated universe the thermal equilibrium with the horizon is not possible, non-relativistic matter may, and dark energy might though only approximately. Ref: JPM and Diego Pavón, Phys. Rev. D94, 103507 (2016) |
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Title: Pre-inflationary imprints in the CMB: the case for smooth transitions. Speaker: João Morais (University of Basque Country - UPV/EHU) Abstract: Within the third quantization picture of quantum cosmology, quantum effects lead to the appearance of extra terms in the effective Friedmann equation. These terms could leave imprints of a pre-inflationary era on the CMB if inflation does not last for too long, i.e., in a scenario of "just enough inflation". In this talk, we discuss how the matching conditions for the cosmological perturbations, as deduced by Deruelle and Mukhanov back in 1995, for an instant phase transition lead to a discontinuity in the Mukhanov-Sasaki variables at the onset of inflation. This ultimately leads to a strong enhancement of the $C_l$ power spectrum, incompatible with the observational constraints. We then propose a more smooth phase transition and show that it can lead to a suppression of the power spectrum for $l<30$, not only satisfying the observational constraints but also appeasing somewhat the CMB anomaly in the large angular scale range. |
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Title: Dark energy disformal interactions. Speaker: Nelson Nunes (Instituto de Astrofísica e Ciências do Espaço, Lisbon) Abstract: I will present the most complete dynamical system analysis consisting of a canonical scalar field conformally and disformally coupled to both dust and radiation. I will comment on constraints imposed on the disformal coupling from Big-Bang Nucleosynthesis and given local and cosmological limits on the variation of the fine–structure constant. |
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Title: Inflation in higher-derivative gravity. Speaker: Sergei Odintsov (ICREA and ICE - CSIC, Barcelona) Abstract: The discussion of inflation in HD gravity model will be presenterd. The HD QG will be considered. The unification of inflation with DE will be outlined. |
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Title: Natural Inflation on the brane with a TeV-scale gravity: Parameter constraints after Planck 2015. Speaker: Grigorios Panotopoulos (Universidad de Lisboa) Abstract: We have studied Natural Inflation (NI) in the framework of the Randall–Sundrum II (RS-II) brane model in the light of the latest Planck results. Adopting the Randall–Sundrum fine-tuning, the model is characterized by three parameters in total, namely the five-dimensional Planck mass and the two mass scales of the inflaton potential f and Λ. We show in the {ns –r} plane the theoretical predictions of the model together with the allowed contour plots, and we conclude that the model is viable. By using the Planck results only, it is possible to determine the two mass scales of the inflaton potential in terms of M5 , which remains undetermined. However, there are several good theoretical reasons to consider a higher-dimensional Planck mass of the order of 10 TeV, which is compatible with primordial nucleosynthesis. If we insist on con- sidering a M5 of this order of magnitude, all parameters are known. |
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Title: The effective number of neutrinos: standard and non-standard calculations. Speaker: Sergio Pastor (Depto. Física Teórica & IFIC, UV-CSIC) Abstract: We have performed a new numerical calculation of the decoupling process of cosmological neutrinos including flavor oscillations, taking into account the full set of differential equations for the neutrino density matrices. Our results are important for fixing the radiation content of the Universe in the standard case in terms of Neff, recently measured by Planck. We also show to which extent the value of Neff can be enhanced in the presence of non-standard neutrino interactions with electrons. We have also considered the case of a very low-reheating scenario, where the last radiation-dominated phase of the Universe begins at temperatures as low as MeV and the thermalization of the neutrino background could be incomplete due to the lack of interactions, leading to Neff < 3. We will show the corresponding bounds on the reheating temperature both from BBN and from late-time cosmological observables, including Planck data. |
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Title: Looking for observational imprints of the mutiverse in the properties of our universe. Speaker: Salvador Robles-Pérez (EEBM-IFF) Abstract: The multiverse has become the most general scenario in modern cosmology and there are now more and more groups looking for the observational imprints that different phenomena in the multi verse would leave in the properties of a universe like ours. In the talk we shall present the basics of the so-called interacting multiverse and some of the imprints it should leave in the properties of our own universe. |
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Title: Revisiting Weyl Unified Theory. Speaker: Carlos Romero (UFPB, Brazil) Abstract: In 1918, H. Weyl proposed a unified theory of gravity and electromagnetism based on a generalization of Riemannian geometry. In spite of its elegance and beauty, a serious objection was raised by Einstein, who argued that Weyl's theory was not suitable as a physical theory . According to Einstein, the theory led to the prediction of a "second clock effect", which is not observed by experiments. We briefly revisit this point and argue that a preliminary discussion on the very notion of proper time is needed in order to consider Einstein's critical point of view. We also point out that a recent proposal by V. Perlick seems to provide a partial solution to this problem. |
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Title: Cosmological constraints on a Unified Dark Matter scalar field model with fast transition. Speaker: Alberto Rozas (Institute of Astrophysics and Space Sciences, University of Lisbon) Abstract: We study the observational viability of a Unified Dark Matter scalar field model with fast transition. For this purpose, we use a combination of geometric probes, some low redshift ones, and some high redshift ones (CMB related included). The Bayesian analysis done reveals that no correlation between the standard cosmological parameters and the ones that characterize the transition is found relevant. This fact allows to further study the transition parameters, which reveals that used data, at background level, can discard this UDM model with slow transition in favor of the faster one. Besides, model comparison with LCDM does not discard the UDM model presented here. |
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Title: Born-Infeld gravity as a cure to spacetime singularities. Speaker: D. Rubiera-García (Institute of Astrophysics and Space Sciences (IA), Lisbon) Abstract: Born-Infeld gravity is a family of extensions of General Relativity that has provided some interesting contributions to astrophysics, black hole physics and cosmology in the last few years. In this talk I will review the motivations and various formulations of this theory, with special emphasis in the most remarkable results regarding the avoidance of spacetime singularities in black hole and cosmological models. |
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Title: CMB for analytical model of wiggly and superconducting cosmic strings. Speaker: Ivan Rybak (Institute of Astrophysics and Space Sciences (IA), Porto) Abstract: We studied how the presence of wiggles affects the evolution of a cosmic string network and how it can change the CMB prediction. Previous study of the CMB spectrum from analytical models of wiggly cosmic strings didn't take into account the full description of their evolution: the contribution from wiggles was taken into account only by additional phenomenological constant term. Here we are going to present the full model for wiggly cosmic strings together with their contribution to the CMB. Additionally we will build the CMB spectrum for superconducting cosmic strings. |
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Title: Probing Cosmic Superstrings with Gravitational Waves. Speaker: Lara Sousa (Institute of Astrophysics and Space Sciences (IA), Porto) Abstract: We compute the stochastic gravitational wave background generated by cosmic superstrings using a semianalytical velocity-dependent model to describe their dynamics. We show that heavier string types may leave distinctive signatures on the stochastic gravitational wave background spectrum within the reach of present and upcoming gravitational wave detectors. We examine the physically motivated scenario in which the physical size of loops is determined by the gravitational backreaction scale and use NANOGrav data to derive a conservative constraint of GμF<3.2×10-9 on the tension of fundamental strings. We demonstrate that approximating the gravitational wave spectrum generated by cosmic superstring networks using the spectrum generated by ordinary cosmic strings with reduced intercommuting probability (which is often done in the literature) leads, in general, to weaker observational constraints on GμF. We show that the inclusion of heavier string types is required for a more accurate characterization of the region of the (gs,GμF) parameter space that may be probed using direct gravitational wave detectors. In particular, we consider the observational constraints that result from NANOGrav data and show that heavier strings generate a secondary exclusion region of parameter space. |
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Title: Unifying inflation with the axion, dark matter, baryogenesis and the seesaw mechanism. Speaker: Carlos Tamarit (Durham University, UK) Abstract: A minimal extension of the Standard Model (SM) with a single new mass scale and providing a complete and consistent picture of particle physics and cosmology up to the Planck scale is presented. We add to the SM three right-handed SM-singlet neutrinos, a new vector-like color triplet fermion and a complex SM singlet scalar $\sigma$ that stabilises the Higgs potential and whose vacuum expectation value at $\sim 10^{11}$ GeV breaks lepton number and a Peccei-Quinn symmetry simultaneously. Primordial inflation is produced by a combination of $\sigma$ (non-minimally coupled to the scalar curvature) and the SM Higgs. Baryogenesis proceeds via thermal leptogenesis. At low energies, the model reduces to the SM, augmented by seesaw-generated neutrino masses, plus the axion, which solves the strong CP problem and accounts for the dark matter in the Universe. The model predicts a minimum value of the tensor-to-scalar ratio $r\simeq 0.004$, running of the scalar spectral index $\alpha\simeq - 7\times 10^{-4}$, the axion mass $m_A\sim 100 \mu eV$ and cosmic axion background radiation corresponding to an increase of the effective number of relativistic neutrinos of $\sim 0.03$. It can be probed decisively by the next generation of cosmic microwave background and axion dark matter experiments. |
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Title: Higgs-curvature coupling and post-inflationary vacuum instability. Speaker: Francisco Torrentí (IFT UAM/CSIC) Abstract: Current measurements of the top quark and Higgs masses suggest that the Standard Model potential becomes negative at very high energies. This can make the Higgs field unstable in the early Universe. In my talk, I will focus on the potential instability during the era of preheating following inflation. In particular, inflaton oscillations during this epoch induce rapid changes in the spacetime curvature. If the Higgs possesses a large enough non-minimal coupling to the scalar curvature, the strong gravitational particle creation triggers a transition to a negative-energy Planck scale vacuum state, causing the immediate collapse of the Universe. I will discuss how classical real-time lattice simulations can be used to constrain the range of couplings compatible with the Higgs stability after inflation. We will assume a minimal scenario, with an inflaton with parabolic potential and no additional new physics below the Planck scale. |