This talk will be divided into two pieces. In the first part of the talk, I will present the generalized SU(2) Proca theory (GSU2P for short). As a modified gravity theory that introduces new gravitational degrees of freedom, the GSU2P is the non-Abelian version of the well known generalized Proca theory where the action is invariant under global transformations of the SU(2) group. New...
In this talk, we explore the possibility of primordial black holes (PBHs) forming from the gravitational collapse of either the structures virialized during reheating (referred as inflaton halos or inflaton clusters), or from the collapse of the central core of these configurations (referred as inflaton stars). We compute the threshold amplitude for the density contrast to undergo this...
Antisymmetric tensor field (two-form field) is a ubiquitous component in string theory and generally couples to the scalar sector through its kinetic term. In this paper, we propose a cosmological scenario that the particle production of two-form field, which is triggered by the background motion of the coupled inflaton field, occurs at the intermediate stage of inflation and generates the...
We examine the validity of the classical approximation of the waterfall phase transition in hybrid inflation from an effective field theory (EFT) point of view. The EFT is constructed by integrating out the waterfall field fluctuations, up to one-loop order in the perturbative expansion. Assuming slow-roll conditions are obeyed, right after the onset of the waterfall phase, we find the...
Identifying the particle content of inflation is one of the most important targets of primordial cosmology. In this respect, how the masses and spins of new particles active during inflation can be read off from the statistical properties of primordial density fluctuations is well understood. However, not when the propagation speeds of the new degrees of freedom and of the...
We investigate the structure of quark stars in the framework of $f(R)=R+\alpha R^2$ gravity using an equation of state for cold quark matter obtained from perturbative QCD, parametrized only by the renormalization scale. We show that a considerably large range of the free parameter $\alpha$, within and even beyond the constraints previously reported in the literature, yield non-negligible...
We study the polarizations of gravitational waves (GWs) in generic higher-curvature gravity (HCG) whose Lagrangian is an arbitrary polynomial of the Riemann tensor. On a flat background, the linear dynamical degrees of freedom in this theory are identified as massless spin-2, massive spin-2, and massive spin-0 fields. Employing a fully gauge-invariant formalism, we demonstrate that (i) the...
In general, modified gravity theories can be seen as dark energy theories using the effective fluid approach. In this work, we apply this formalism to the most general second-order scalar-vector-tensor (SVT) theory of gravity. This will allow us to encompass all the free functions of the theory in terms of the equation of state, speed of sound, velocity, and anisotropic stress of a very...
In this paper, we have emphasized the stability analysis of the accelerating cosmological models obtained in $f(T)$ gravity theory. The behaviour of the models based on the evolution of the equation of state parameter shows phantom-like behaviour at the present epoch. The scalar perturbation technique is used to create the perturbed evolution equations, and the stability of the models has been...
The detection of gravitational waves (GW) has opened a new window for cosmology. The current tension between the measurement of the Hubble constant H0 from Cosmic Microwave Background and Supernova analyses makes an independent, standard siren measurement of H0 from gravitational waves particularly interesting.
However, up to date, the astronomical community has confidently identified only...
Since the first gravitational wave detection from a merging binary black hole system by the large interferometers LIGO, a new window of the Universe was opened leading us to use these waves to probe the expansion of the Universe. Gravitational wave sources with electromagnetic counterparts, called bright standard sirens, are very useful to cosmology as their luminosity distances can be...
We investigate a recently proposed method for measuring the Hubble constant from gravitational wave detections of binary black hole coalescences without electromagnetic counterparts. In the absence of a direct redshift measurement, the missing information on the left-hand side of the Hubble-Lemaître law is provided by the statistical knowledge on the redshift distribution of sources. We assume...
We study kink-antikink scattering in the sine-Gordon model in the presence of interactions with an additional scalar field, ψ, that is in its quantum vacuum. In contrast to the classical scattering, now there is quantum radiation of ψ quanta and the kink-antikink may form bound states that resemble breathers of the sine-Gordon model. We quantify the rate of radiation and map the parameters for...
The BINGO instrument is being constructed with the goal to be the first radio telescope to detect Baryonic Acoustic Oscillations (BAO) in the radio frequency band (~ 1 GHz) using the 21 cm hyperfine transition of the neutral hydrogen using an observation technique known as intensity mapping (IM). However, the 21 cm signal is a few orders of magnitude weaker than the emission from other...
The 21 cm hydrogen line is arguably one of the most powerful probes to explore the Universe, from recombination to the present times. To recover it, it is essential to separate the cosmological signal from the much stronger foreground contributions at radio frequencies. The Baryon Acoustic Oscillations from Integrated Neutral Gas Observations (BINGO) radio telescope is designed to measure the...
With the recent development of projects for the gathering of cosmological data through radioastronomy, mainly using the redshifted 21 cm signal line, various systematic effects have been analysed to improve sensibility and precision. This includes instrumental features such as beam analysis, which involves studying the how the reflectors modify the data through optical aberrations, and how it...
New degrees of freedom active during inflation lead to nontrivial signatures across scalar and tensor primordial spectra. We will discuss how such deviations from single-field, slow-roll inflation, manifested as particle excitations, lead to distinct signals in the stochastic gravitational wave background generated during inflation and how its characteristics are related to sharp features of...
Boson-stars are self-gravitating Bose-Einstein condensates of ultra-light boson fields, which are widely considered as strong candidates to account for at least part of Dark Matter. Boson-star mergers can produce gravitational-wave signals observable by current detectors such as Advanced LIGO and Virgo. I will present a systematic comparison of existing (high-mass) gravitational-wave signals...
The supernova, which is the event at the last moment of the massive star's life, is the next promising candidate as the gravitational wave source. Up to now, gravitational waves from supernova explosions have been mainly discussed via numerical simulation. These results tell us the existence of the gravitational waves whose frequencies increase from a few hundred hertz up to kHz within a...
The Gibbons-Maeda-Garfinkle-Horowitz-Strominger (GMGHS)
black hole is an influential solution of the low energy heterotic
string theory. As it is well known, it presents a singular extremal
limit. We construct a regular extension of the GMGHS extremal black
hole in a model with $\mathcal{O}(\alpha')$ corrections in the action,
by solving the fully non-linear equations of motion....
The standard cosmological model, namely the flat LCDM model, has been tremendously successful in describing cosmological observations for over two decades. Still, it suffers from theoretical caveats, in addition to recent problems like the SH0ES tension between H0 measurements from the early- and late-time Universe. In light of these issues, I will show results of some null tests of...
We perform a general test of the ΛCDM and wCDM cosmological models by comparing constraints on the geometry of the expansion history to those on the growth of structure. Specifically, we split the total matter energy density, Ωm , and (for wCDM) dark energy equation of state, w, into two parameters each: one that captures the geometry, and another that captures the growth. We constrain our...
We test the usual hypothesis that the Cosmic Microwave Background (CMB) dipole, its largest anisotropy, is due to our peculiar velocity with respect to the Hubble flow by measuring independently the Doppler and aberration effects on the CMB using Planck 2018 data. We remove the spurious contributions from the conversion of intensity into temperature and arrive at measurements which are...
Dark matter not only provides the invisible scaffolding from which the birth of galaxies takes place, but by studying its distribution in our Universe we can infer a great deal of information regarding the growth of structure and cosmic expansion. Measuring the gravitational lensing of the CMB allows the mapping of all the matter distribution (for which the majority is dark matter) to very...
We explore observational signatures from multi-field inflationary models with more than two fields. We first revisit the two-field case where the attractor solution with either small or large turn rate can be found analytically and investigate under what conditions the same procedure can be generalised for more fields. For three fields in the slow-roll, slow-twist and extreme turning regime we...
The problem of finding a vacuum definition for a single quantum field in curved spaces is discussed under a new geometrical perspective. The minimum complex structure in phase space necessary to define a vacuum state is mapped to a 2-dimensional hyperbolic space in which distances can be defined. It is shown that well known vacuum prescriptions in the literature correspond to points in this...
In this work we analyze the stability criteria in $f(R)$ theories of gravity in the metric formalism under the approach of a thermodynamics analogy proposed in [C.D. Peralta and S.E. Jorás JCAP06(2020)053] for $\phi^4$ and double well inflationary potentials. We starting from the mentioned potentials in the Einstein frame, and obtain a parametric form of $f(R)$ in the corresponding Jordan...
Gravitational arcs are strongly magnified images of distant galaxies (known as sources) caused by the deflection of light produced by a foreground galaxy or galaxy cluster (the lens). This strong lensing phenomenon has been used to study high-redshift sources, to assess the mass distribution in the lens, to constrain cosmological parameters and to set limits on modified gravity. In addition,...
We study the E and B mode polarisation of the cosmic microwave background (CMB) originating from the transverse peculiar velocity of free electrons during reionisation and post reionisation era. Interestingly, apart from having a blackbody part, the spectrum also contains a Sunyaev Zel'dovich (SZ) type (y-type) distortion, which makes it distinguishable from primordial polarisation as well as...
In this talk I will introduce a new CMB lensing power spectrum estimator for deep polarisation surveys. Thanks to the B modes of polarisation produced by gravitational lensing, upcoming surveys will optimally reconstruct the lensing field by iteratively delensing the observed polarisation maps. I will show that despite the increased complexity of the reconstructed lensing map, its power...
The generation of non-Gaussianity during inflation is often viewed in the context of perturbative processes producing small amounts of non-Gaussianity correlated with an underlying Gaussian field. However, there exist physical mechanisms by which non-Gaussianity can be produced non-perturbatively and in novel forms which are poorly modeled by the data templates used in current analysis. We...
It is interesting to know whether or not we can determine black-hole's parameters such as the mass, spin, inclination angle, and distance only from the information of black-hole's shadow. In this work, assuming a non-spinning black hole, i.e., a Schwarzschild black hole, with an infinitely thin accretion disc for simplicity, we show that the system's parameters such as the angular...
Oscillons are localized field configurations oscillating in time with lifetimes orders of magnitude longer than their oscillation period. This talk shows the deformation of one-dimensional breather solutions of the sine-Gordon (SG) equation into oscillons. SG equation is deformed by a radial damping term present in the d-dimensional Laplacian. Oscillons are evaluated (a) in a regime of...
If a pseudoscalar inflaton couples to the topological charge density of a non-Abelian gauge field, it can decay into gauge bosons that may thermalize quickly due to their self-interactions. In the resulting medium, non-Abelian ``strong sphaleron'' interactions increase the thermal friction felt by the inflation field, which can in turn lead to a self-amplifing and efficient reheating after...
We study quantum cosmology of the 2D Jackiw-Teitelboim (JT) gravity with Λ > 0 and calculate
the Hartle-Hawking (HH) wave function for this model in the minisuperspace framework. Our
approach is guided by the observation that the JT dynamics can be mapped exactly onto that of
the Kantowski-Sachs (KS) model describing a homogeneous universe with spatial sections of S1×S2
topology. This...
Phase Transitions as Cosmological Witnesses
4 May 2020, 15:15
15m
Parallel Talk Cosmology Cosmology I
Speaker
Dan Vagie
Description
We study the gravitational wave background from a first order phase transition generated during standard and nonstandard cosmological histories. We analyze the hydrodynamic properties of the plasma to define a self-similar invariant velocity profile to be...
In this talk, I will present the hybrid lagrangian bias expansion and how we can use it to make predictions for the auto and cross bispectra up to non-linear scales. I will show that the third-order bias expansion is enough to describe all triangular configurations of the bispectrum up to scales $\sim 0.6$ Mpc$/h$. We used N-body simulations and a subhalo abundance matching model to test the...
