Most cosmologists today believed that our universe corresponds to a Big Bang homogeneous (FLRW) metric with an age which is only three times larger than the age of Earth. This seems in agreement with most observations and with the cosmological principle which states that spacetime is homogeneous only in space, but not in time. Recent measurements indicate that our cosmic expansion is...
Compact astrophysical objects like black holes and neutron stars are excellent tools to test the strong gravity regime of General Relativity and alternative gravity theories by comparing their theoretical predictions with current and future observations, since alternative gravity theories may feature distinctive signatures for these compact objects. While the analysis of the properties of...
Unparticles are a hypothetical new form of matter created from fermions in an SU(N) gauge theory. Unparticles provide a wide spectrum of new cosmological applications. In my talk (based on arxiv:2010.02998 and arxiv: 1912.10532), I will show that they can display a cosmological-constant-like behavior, and since then they can be used to generate cosmic inflation or dark energy. I will show...
In the 90s it was shown that the Einstein equation could be understood as an equation of state, general relativity as the equilibrium state of gravity, and f(R) gravity as a non-equilibrium one. In this presentation I discuss how the application of Eckart's first order thermodynamics to the effective dissipative fluid describing scalar-tensor gravity leads to a thermodynamics for the space of...
Recently the entanglement entropy between universes has been calculated, an entropy which somehow describes the quantumness of a homogeneous multiverse. The third quantization formalism of canonical quantum gravity is used here. Improvements of the results in a more general scenario will be shown, studying what happens at critical points of the evolution of a classical universe. Besides, we...
The primordial abundance of lithium is still a subject of controversy, given the disagreement between numerical results and observational estimates. We show how this discrepancy can be understood in the context of variation of fundamental constants at the epoch of Big Bang Nucleosynthesis. The variation of Newton's constant plays a crucial role. In particular, its interpretation in terms of...
Using the logarithmic superfluid model, one can formulate quantum post-relativistic theory of superfluid vacuum, which contains special and general relativity in the “phononic” (low-momenta) limit, but differs at higher momenta. According to the theory, an effective gravitational potential is induced by the quantum wavefunction of physical vacuum in a stationary state, while the vacuum itself...
The accelerated expansion of the Universe implies the existence of an energy contribution known as dark energy. Associated with the cosmological constant in the standard model of cosmology, the nature of this dark energy is still unknown. In this talk I will discuss an alternative gravity model in which this dark energy contribution emerges naturally, as a result of allowing for a...
The principle of finite amplitudes postulates that semi-classical transition amplitudes from the early universe up to current field values should be well defined. We will show in this talk that the application of this simple principle has strong theoretical constraining power for fundamentally motivated alternative theories of gravity and their solutions for the very early universe. In...
If we are so eager to modify gravity, why can´t we modify string theory?, which in turn can give us even more modified gravity theories. For example the string tension does not have to be put in by hand, it can be dynamically
generated, as in the case when we formulate string theory in the modified measure formalism.
For gravity theories, the modified measure formalism gives a dynamical...
We reconsider the dynamical systems approach to analyze inflationary universe in the Jordan frame models of scalar field nonminimally coupled to curvature or torsion. The adopted set of variables allows us to clearly distinguish between different asymptotic states in the phase space, including the kinetic and inflationary regimes. Inflation is realized as a heteroclinic trajectory originating...
Both a metric and a tetrad $3+1$ formulation for a general affine connection is developed while also assuming nonmetricity. By splitting the space-time metric and tetrad into their spatial and temporal parts as well as through finding the Gauss-like equations for any tensor through which gravity is expressed, a general foundation for the formalisms is set up. Based on this foundation the...
In the semi-classical regime, quantum fluctuations embedded in a Riemannian spacetime can be effectively recast as classical back reactions and manifest themselves in the form of non-minimal couplings between matter and curvature. In this work, we exhibit that this semi-classical description can also be applied within the Teleparallel formulation. In the Teleparallel description, quantum...
In this work, we investigate gravitational baryogenesis in the framework of f(P) gravity to understand the applicability of this class of modified gravity in addressing the baryon asymmetry of the Universe. For the analysis, we set f(P)=αP where α is the model parameter. We found that in f(P) gravity, the CP-violating interaction acquires a modification through the addition of the...
Euclid is an ESA medium class astronomy and astrophysics space mission. Euclid was selected by ESA in October 2011 and its launch is planned for 2022. Euclid will explore how the Universe evolved over the past 10 billion years to address questions related to fundamental physics and cosmology..
I will give a general overview of the Euclid satellite and its mission, and describe the main...
Abstract:
Recent observations carried out using all 4 VLTs simultaneously have provided new quasar spectra of unprecedented quality. I will describe the very recent analysis of such data, carried out using new AI methods and other statistical tools that permit fully automated and unbiased estimates of the fine structure constant at high redshift.
We introduce a quantum interferometric scheme that uses states that are sharp in frequency and delocalized in position. The states are frequency modes of a quantum field that is trapped at all times in a finite volume potential, such as a small box potential. This allows for significant miniaturization of interferometric devices. We consider a concrete implementation using the ground state and...
Where, I venture into how the noise in gravitational wave detectors could tell us about the physics beyond the standard model of particle physics, and the fundamental nature of quantum black holes.
I will present an impact of alternative theories of gravity on low-mass (sub-)stellar objects' evolution and properties. I will also demonstrate how seismic data acquired from earthquakes and marsquakes could be use to test theories of gravity.
CGHS black holes have rightfully garnered much attention over the last few decades as the models are simplified (1+1)-dimensional versions of black hole evaporation. Their solubility has lead to tractable physical insights into the radiative process. Concurrently, moving mirrors are well-known simplified (1+1)-dimensional models for black hole evaporation. We synthesize the two by finding an...
It is an observationally established fact that dark matter forms large scale structures in the intergalactic space. However it is not fully known if any structures can emerge on the stellar scale and if so, what would they look like.
In this short talk I will discuss the possibilities of the emergence of axionlike particle (ALP) clouds around compact objects, such as black holes. Using...
This work explores the effects of charge on a peculiar stellar object, recognized as gravastar, under the influence curvature-matter coupling gravity. The gravastar is also known as an alternative to a black hole and is expressed by three distinct domains named as (i) the interior domain, (ii) the intermediate shell and (iii) the exterior domain. We analyze these domains for a specific...
The fate of matter forming a black hole is still an open problem, although models of quantum gravity corrected black holes are available. In loop quantum gravity (LQG) models were presented, which resolve the classical singularity in the centre of the black hole by means of a black-to-white hole transition, but neglect the collapse process. The situation is similar in other quantum gravity...
Amplitude methods have shown to be a promising technique to perform Post-Minkowskian calculations used as inputs to construct gravitational waveforms. In this talk, I will show how to extend these methods beyond GR. As proof of principle, I will consider spinless particles conformally coupled to a gravitational helicity-0 mode. This setup leads to subtleties in the matching procedure used to...
During the last years many inspired Loop Quantum Gravity (LQG) models for homogeneous cosmology were carefully studied, however all these models required extra input to be self consistent. In this talk I will briefly present a gauge fixed version of LQG adapted to cosmological systems. The interesting feature of this model is the resulting cosmological dynamics: by using the full structure of...
We will review our previous work on precanonical quantization of GR and the recent work on precanonical quantization of the teleparallel equivalent of GR. Both approaches are based on Palatini formulations in vielbein variables and the analysis of constraints within the De Donder-Weyl Hamiltonian formulation which treats space and time variables on equal footing. In both theories, we obtain...
In non-smooth and discrete metric spaces of some models of quantum gravity, e.g., those based on Ricci calculus, it is a nontrivial task to introduce a notion of curvature that works at any length scale down to the cutoff scale and in the continuum limit converges to a curvature defined in terms of the Riemann tensor. The recently introduced quantum Ricci curvature has those properties. In...
Higher order extensions of Einstein gravity play important roles in various areas such as cosmology, the early universe or quantum gravity. In this talk, I will take a look into quantum properties of general higher order extensions of gravity provided that they depend on the Riemann tensor and the inverse metric. Using the functional renormalisation group, a flow equation for such theories is...
There is an increasing interest in cosmological models with scalar fields that present kinetically dominated phases in their evolution, since these may have played a relevant role in the very early stages of the Universe and lead to modifications in observable quantities, e.g. the cosmic microwave background. The departures of this scenario from standard slow-roll inflation prevent one for...
The exact one-loop beta functions for the four-derivative terms (Weyl tensor squared, Ricci scalar
squared, and the Gauss-Bonnet) are derived for the minimal six-derivative quantum gravity (QG)
theory in four spacetime dimensions. The calculation is performed by means of the Barvinsky and
Vilkovisky generalized Schwinger-DeWitt technique. With this result we gain, for the first time,...
The Cosmic Microwave Background temperature and polarization anisotropy measurements have provided strong confirmation of the LCDM model of structure formation. Even if this model can explain incredibly well the observations in a vast range of scales and epochs, with the increase of the experimental sensitivity, a few interesting tensions between the cosmological probes, and anomalies in the...
The standard cosmological model, LCDM, is based on General relativity and assumes the Universe is made of a Dark energy component in the form of a cosmological constant (L). Although LCDM gives an astonishing description of the Universe, the model shows some shortcomings: the so-called cosmological constant problems.Furthermore, some mild observational tensions among different datasets...
In the previous works, using the SALT measurements of three luminous quasars, we confirmed the presence of the Broad Line Region radius-luminosity relation for the ultraviolet line of MgII. Together with SDSS-RM as well as Oz-DES datasets, we studied the classical as well as extended versions of the radius-luminosity (RL) relation. Using 78 sources, we simultaneously fitted the parameters of...
We analyse the emergent cosmological dynamics corresponding to the mean field hydrodynamics of quantum gravity condensates, in the tensorial group field theory formalism. We focus in particular on the cosmological effects of fundamental interactions, and on the contributions from different quantum geometric modes. The general consequence of such interactions is to produce an accelerated...
ΛCDM model to date remains the best observationally fitting model for late time cosmology. However, this model suffers from the theoretical issue that the quantum vacuum energy, which is the only known candidate for Λ, gives from QFT calculation a value that mismatches with the observed value of Λ by orders of magnitude. This theoretical issue motivated the search for alternative late-time...
In the first part of this talk, I will review the Hubble tension and then describe some theoretical efforts to alleviate it---as well as the discrepancy with the BAO Lyman-α data — via the dark energy models that yield negative density values in the past. I will then discuss a recent work with two minimal extensions of the ΛCDM model, together or separately, can realize such a scenario: (i)...
I will motivate how moving beyond the FLRW paradigm may be the only way to resolve Hubble tension.
In this paper we have investigated a bulk viscous universe in $f(R,T)$ gravity where $R$ and $T$ are the Ricci scalar and trace of energy momentum tensor respectively. We have obtained explicit solutions of field equations in modified gravity by considering the power law form of scale factor. The Hubble parameter and deceleration
parameter are derived in terms of cosmic time and redshift...
Cosmological tensions in recent measurements of both Hubble expansion and the growth of structure in the Universe has led to a reconsideration of certain aspects of the concordance model of standard cosmology. One part of this comes from the growing tension between observations that are independent of cosmological models against others that are dependent on $\Lambda$CDM. To this end, the...
The recent gravitational wave observations of the collision of black holes and neutron stars have allowed us to pierce into the extreme gravity regime, where gravity is simultaneously unfathomably large and wildly dynamical. These waves encode a trove of information about physics that is prime for the taking, including potential revelations about the validity of Einstein's theory. In this...
Gravitational lensing of light is a well established test of gravity. However, little is known about how gravitational waves (GW) propagate beyond the simplest space-times in theories beyond Einstein’s General Relativity (GR). I will present a framework for GW lensing beyond GR at leading order in frequency. The modified causal structure and kinetic mixing between metric and additional degrees...
We study the effects of cosmological vector fields on the propagation of gravitational waves (GWs). The so-called dark sector in Cosmology remains unexplained, even though it makes up most of the content of the Universe. This fact has led to the proposal of several models of dark matter, dark energy or dark radiation. Among them, we can find some based upon vector fields (such as ultralight...
Gravitational waves (GWs) have opened a new window of fundamental physics in a number of important ways. The next generation of GW detectors may reveal more information about the polarization structure of GWs. Additionally, there is growing interest in theories of gravity beyond GR. One such theory which remains viable within the context of recent measurements of the speed of propagation of...
The GRAVITY Collaboration achieved the remarkable detection of the orbital precession of the S2 star around the Galactic Centre supermassive black hole, providing yet another proof of the validity of the General Relativity. The departure from the Schwarzschild precession is encoded in the parameter $f_{\rm SP}$ which multiplies the predicted general relativistic precession. Such a parameter...
The late universe contains a wealth of information about fundamental physics and gravity, wrapped up in non-Gaussian fields. To make use of as much information as possible it is necessary to go beyond power spectra. Rather than going to higher order N-point correlation functions, this talk will demonstrate that the probability distribution function (PDF) of spheres in the matter field (a...
We reconstruct the Hubble function using late-time cosmological data sets and use it to draw out Horndeski theories that are fully anchored on the expansion history. We discuss various formalisms for the inversion of the modified Friedmann equations and complement this with the reconstructed Hubble data to obtain predictive constraints on the Horndeski potentials and the dark energy equation of state.
Screening mechanisms in Extended Theories of Gravity (ETGs) are essential to make theories able to pass Solar System constraints and, at the same time, possibly driving the accelerated expansion of the Universe at large scales (thus behaving as dark energy). In our work, we have considered an ETG belonging to the family of Degenerate High-Order Scalar-Tensor theories (DHOST) and characterized...
The non-product spectral geometry may lead to models that possess features characteristic to bimetric gravity theories. Starting from the pair of Friedmann–Lemaître–Robertson–Walker metrics on the product geometry and mildly modifying the Dirac operator we end up with a class of models that have a nontrivial interacting potential term, and their solutions are stable for several cosmological...
General relativity has been very successful in describing gravity. However, cosmological observations such as the dark sector of the universe, the value of the cosmological constant, and the Hubble constant give indications to new physics. This might be explained by modified theories of gravity. What has often been overlooked is that general relativity has different equivalent descriptions....
The polynomial affine gravity is an alternative model to describe gravitational interactions using the affine connection as the sole mediator. The action is built using a sort of dimensional analysis technique and preserving the invariance under diffeomorphisms. Interestingly, the coupling constants are dimensionless, which is desirable from a quantum field stand point. In $3+1$ dimensions...
From the study of relativistic dynamics of fluids out of equilibrium in a curved background, a new cosmological framework, dubbed Ricci Cosmology, has emerged in which linear terms in Ricci scalar and Ricci tensor lead to modifications of the equilibrium pressure in the energy-momentum tensor in the fluids filling the Universe. The coefficients in front of such terms are called second order...
Abstract
After the recent detection of GW170817, the most interesting terms of Horndeski theory were severely
constrained. Nevertheless, the analog of Horndeski theory in the Teleparallel Gravity framework is far richer in structure since the extra term in the Lagrangian, Ltele emerges.
As a result, the terms that were eliminated in standard Horndeski theory could, in this case,...
Scalar Tensor Vector Gravity (STVG) is a metric theory of gravity with dynamical scalar fields and a massive vector field introduced in addition to the metric tensor. In the weak field approximation STVG modifies the Newtonian acceleration with a Yukawa like repulsive term due to Maxwell-Proca type Lagrangian. This associates matter with a fifth force and a modified equation of motion.STVG has...
CDT is a numerical approach to quantum gravity which attempts to describe our Universe with the help of Regge Calculus and Path Integral formalism. The study of the past years revealed the rich phase-diagram of the model, which contains a physical de Sitter phase with higher order phase-transitions on its boarders. Recently we added scalar fields to the model. The classical fields were used as...
In the context of the late time cosmic acceleration phenomenon, many geometrically
modified theories of gravity have been proposed in recent times. In this paper, we have investigated the role of a recently proposed extension of symmetric teleparallel gravity dubbed as f(Q,T) gravity in getting viable cosmological models, where Q and T respectively denote the non-metricity and the trace of...
Flat space theories of spinning particles must obey nontrivial consistency conditions that follow from locality, unitarity and gauge invariance. These conditions are especially powerful in the case of Lorentz invariant theories of massless particles, where they have been used to derive the gravitational equivalence principle, among other interesting results. In a recent paper, we have shown...
Taking the minimalistic approach, within MSSM, we propose the model of inflation in which the inflaton field is a scalar component of the MSSM state(s).
The proposed model turns out to be very predictive. The inflationary phase is fully governed by the MSSM Yukawa superpotential couplings. The values of the scalar spectral index and the tensor-to-scalar ratio are predicted to be ns≃0.966 and...
Based on connections between gravity and thermodynamics, interpreting the dynamics of the universe as a quest for achieving holographic equipartition is a novel concept proposed by Padmanabhan. However, the generalization of Padmanabhan's conjecture to the non-flat universe had resulted in uncertainty about the choice of volume. We have shown that the exact mathematical formulation of the...
By proposing an appropriate dynamical deformation between the momenta associated with the scalar field (of the Sáez–Ballester theory) and scale factor of the spatially flat FLRW metric, we establish a modified cosmological model. Subsequently, for some particular cases, by focusing on the early epoch of the universe, we show that our model provides a more successful description for evolution...
I discuss in this talk a new formulation of dark-matter (DM) coupling to gravity. Unlike the Standard Model (SM) sector which couples to the metric, DM couples to the spacetime affine connection through a $Z_2$-symmetry breaking term. I will show that such a structure allows DM to be only scalar particles (unlike the other alternative gravities). I discuss the different decay modes of DM in...
We will review the Scale Invariant Vacuum idea as related to Weyl Integrable Geometry. Main results related to SIV and inflation [1], the growth of the density fluctuations [2], and application of the SIV to scale-invariant dynamics of Galaxies, MOND, Dark Matter, and the Dwarf Spheroidals [3] will be summarized. If time permits, a potential connection of the weak field SIV results to the...
We present a simple quantum description of the Universe in which the effective de Sitter spacetime geometry emerges from a coherent state of background gravitons. Once localised baryonic matter is added consistently, this quantum state is shown to contain the necessary components to describe MoND phenomenology at galactic scales and possibly explain the tension between values of the Hubble...
We study the relation between quasinormal modes and geodesic quantities recently brought back due to the black hole shadow observation by Event Horizon Telescope. With the help of WKB method we found an analytical relation between the real part of quasinormal frequencies at the eikonal limit and shadow radius of the same black hole. Some examples fulfilling the correspondence are provided.
Testing strong gravity regimes such as the vicinity of black holes is likely to be attainable with the future developments of observing technology. In this talk, adopting a theory-agnostic approach, we first propose a class of Kerr-like rotating black holes, whose Z_2 symmetry is generically broken. We focus on the possibility that such a violation of Z_2 symmetry is induced by the spin of the...
One of the consequences of Einstein’s general theory of relativity is bending of light as it passes through a gravitational field. Examining the path of light in a very strong gravitational field of a black hole can provide a huge amount of information about the geometry and characteristics of the surrounding space.
On the other hand, the path of light rays, extent, and shape of gravitational...
The IceCube neutrino observatory is a neutrino telescope situated near the South Pole in Antarctica. A cubic kilometer of ice is instrumented with optical modules sensitive to photons. When high energetic particles produce light in interactions with the ice, the signature can be recorded and used for reconstruction of the primary particle.
The design of IceCube not only facilitates the...
In recent years there have appeared several constructions of traversable wormholes, in four and other dimensions, which only involve physically acceptable, controllable ingredients. They connect in deep ways many aspects of gravity, quantum field theory, and quantum information. I will discuss several features of these constructions, with a focus on traversability, connectivity between...
Over the last years some interest has been gathered by f(Q) theories, which are new candidates to replace Einstein’s prescription for gravity. The nonmetricity tensor Q allows to put forward the assumption of a free torsionless connection and, consequently, new degrees of freedom in the action are taken into account. This work focuses on a class of f(Q) theories, characterized by the presence...
We perform observational tests on the $f(T) $ gravity using the Cosmic Chronometer data, SNIa data and BAO data together with three different independent measurements of the current value of $H_0$. In this work, we investigate the impact of these priors on five core models in $f(T)$ gravity. In addition, we perform background studies on these models to better distinguish the impacts of the...
Cyclic universes with bouncing solutions are candidates for solving the big bang initial singularity problem. Here I will look for bouncing solutions in the context of modified theories of gravity whose field equations contain up to fourth-order derivatives of the metric tensor. In finding such bouncing solutions I will resort to an order reduction technique that reduces the order of the...
Galaxy clusters constitute a powerful tool to investigate modification of gravity at cosmological scales; in particular, with the combination of cluster’s mass profiles derived with lensing and internal kinematic analyses, it is possible to constrain departures from General Relativity in a complementary way with respect to other cosmological and astrophysical probes. In this context, I will...
We have shown the potential of next-generation astrometric satellites for distinguishing between a cusp and a core in the dark matter density profile. This goal can be achieved with the measure of the proper motions of at least 6000 stars within a nearby dwarf galaxy with an accuracy of 1 km~s$^{-1}$ at most. We have built mock star catalogues similar to those expected in future astrometric...
In this talk I will review the recent results of a numerical study of chameleon gravity in the context of galaxy clusters and cosmic voids. In this study we solved the chameleon field equation for NFW halos and cosmic void density profiles for the currently observationally viable chameleon models. The obtained results shine light on the non-trivial relationship between the NFW halo parameters...
The quasi-static approximation (QSA) is a useful tool to get a quick and clear physical understanding of the phenomenology of modified gravity which is encoded in two functions (of scale and time): the effective gravitational constant (describing the modified evolution of matter perturbations) and the slip (parametrizing the relations between the two gravitational potentials). This...
With the advent of surveys such as the Legacy Survey of Space and Time (LSST), there will be opportunities in the near future to study nonlinear aspects of modified gravity (MG) theories through weak lensing and galaxy clustering measurements. These will be important in constraining the theory space for MG theories with screening effects, which are manifestly nonlinear. As the typical method...
Schemes of gravitationally induced decoherence are being actively investigated as possible mechanisms for the quantum-to-classical transition. In this talk, I introduce a decoherence process attributable to quantum gravity effects. In particular, I assume a foamy quantum spacetime with a fluctuating minimal length coinciding on average with the Planck scale. Considering deformed canonical...
The tools of spectral geometry lead to the derivation of the action functionals both for gauge theories and gravity. The simplest, mildly noncommutative models with a product geometry give the standard Yang-Mills-Higgs models and the General Relativity action with a cosmological constant. An interesting situation occurs when the geometry is not of the product type, thus allowing the metric to...
The idea of massive graviton plays a fundamental role in modern physics as a landmark of most scenarios related to the modification of the theory of gravity. Limits on graviton mass can be obtained with capabilities of multi-messenger astronomy. In particular, non-zero graviton mass would modify estimates of the total cluster mass (Yukawa term influences Newtonian potential). This can be...
The phenomena of standing waves are mostly studied in the context of mechanical or electromagnetic waves. In the context of General Relativity, the issue of how to define standing gravitational waves was addressed by Bondi and later by Stefani. We investigate an expanding universe filled with standing gravitational waves. We study how freely falling particles in this spacetime behave, namely,...
Approaches to Quantum Gravity (QG) often propose a fundamental minimal length scale in Nature irrespective of our measurement precision. This scale is believed to be at or near the Planck length (10^{-35} m), which also makes it unlikely to be probed directly. In this talk, we put forward a mechanism, recently developed by us, which propose an indirect probe to measure some effects of the...
The emergence of $R^2$ inflation which is the best fit framework for CMB observations to date comes from the attempts to attack the problem of quantization of gravity which in turn have resulted in the trace anomaly discovery. Further developments in trace anomaly and different frameworks aiming to construct quantum gravity indicate an inevitability of non-locality in fundamental physics at...
We present a simple quantum description of compact sources and black holes in which the General Relativistic exterior is reproduced by coherent states but the classical central singularity cannot be resolved because modes of arbitrarily short wavelength are not populated. Quantum corrections to the outer potential are also estimated, which could result in observable effects for the...
A number of near-extremal conditions are utilized to simplify the equation of motion of the
neutral scalar perturbations in generalized spherically symmetric black hole background into a differential equation with the Pöschl-Teller potential. An analytic formula for quasinormal frequencies is obtained. The analytic formula is then used to investigate Strong Cosmic Censorship conjectures (SCC)...
Interpreting the cosmological constant ($\Lambda$) as the vacuum energy, and under a minimum amount of assumptions, leads to a deformation in the vicinity of a black hole and a new Kerr–de Sitter solution. The new Kerr–de Sitter solution is a more straightforward and has richer geometric structure than the original one. Interestingly, there exist minimum ($M_{min}$) and maximum ($M_{min}$)...
