Detection of gravitational wave signals from mergers of black holes and neutron stars is one the most important discoveries of this century. I shall briefly present the phenomenon of gravitational radiation as predicted by Einstein's general relativity. I shall describe gravitational wave detectors and
methods of analyzing gravitational wave data. I shall review the observations made during...
I will discuss efficiency factors for the production of gravitational waves through bubble collisions and plasma-related sources in strong phase transitions, and the conditions under which the bubble collisions can contribute significantly to the signal. I will also show that generically the sound-wave period is much shorter than a Hubble time leading to a reduction of GW signal produced by...
Exotic compact objects (ECOs) produce the same initial event detected by LIGO-Virgo collabo-ration as classical black holes (BHs), but various quantum gravity models feature the different following echoes. In particular, we investigate the echoes from the fluctuation-dissipation theorem [1, 2], which changes the dispersion relationship near the (would-be) horizon and results in a Boltzmann...
A rather minimal possibility is that dark matter consists of the gauge bosons of a spontaneously broken symmetry. I will discuss the possibility of detecting the gravitational waves produced by the phase transition associated with such breaking. Concretely, I will focus on the scenario based on an 𝑆𝑈(2)_D group and argue that it is a case study for the sensitivity of future gravitational wave...
The Wilsonian renormalization group (RG) requires Euclidean signature. The conformal factor of the metric then has a wrong-sign kinetic term, which has a profound effect on its RG properties. In particular around the Gaussian fixed point, it supports a Hilbert space of renormalizable interactions involving arbitrarily high powers of the gravitational fluctuations. These interactions are...
In this talk I will briefly introduce the present understanding about the cosmic acceleration at present from the perspective of phenomenological study. I will review the latest observational status of the late-time cosmic acceleration and then depict how to do the model building of dynamical dark energy. Afterwards, I will also give an introduction to a type of torsional based modified...
If the Standard Model vacuum is metastable, bubbles that form expand and convert the entire vacuum into a true vacuum state incompatible with observations. It is sometimes argued, however, that true vacuum bubbles forming during inflation are 'inflated away' and thus pose no danger to the present day universe, even if they form. I will argue that this point of view is incorrect - while the...
Within the framework of $\Lambda$CDM, the local determination of the Hubble constant disagrees -- at the 4.4$\sigma$ level -- with that inferred from the very accurate CMB observations by the Planck satellite. This clearly motivates the study of extensions of the standard cosmological model that could reduce such tension. Proposed extensions of $\Lambda$CDM that reduce this so-called Hubble...
Identification of dark matter has been an outstanding problem in physics for decades, and axion (or axion like partciles) is its candidate with great motivations. A number of observations and experiments have tried to detect axion by using the axion-photon conversion by assuming the axion is coupled to photon, while no signal yet to be found. In this talk, I will discuss new techniques to...
In this talk, I will discuss the methods to search for dark matter or dark sector particles having the masses from GeV to the Solar Mass. We can probe their properties by colliders, neutrino or gamma ray experiments.
Direct detection experiments relying on nuclear recoil signatures lose sensitivity to sub-GeV dark matter for typical galactic velocities. This sensitivity is recovered if there exists another source of flux with higher momenta. Such an energetic flux of light dark matter could originate from the decay of mesons produced in inelastic cosmic ray collisions. I present in this talk the dark...
Incorporating three generations of right-handed Majorana neutrinos to quintessential inflation, we construct a model which simultaneously explains inflation, dark energy, dark matter and baryogenesis. These right-handed neutrinos have hierarchical masses $M_3 \sim 10^{13}$GeV, $M_2 \sim 10^{11}$GeV, $M_1 \sim 10$keV and are produced by gravitational particle production in the kination regime...
1 minute 1 slide oral presentation;
I will give an introductory review talk on extensions of general relativity, covering the following contents.
1. Introduction
2. General relativity and Lovelock gravity
3. PPN formalism
4. EFT approach
5. Massive gravity
6. Summary
Theories of massive gravity and their generalizations have been used for the description of the late time and early universe cosmologies. These theories however are strongly coupled at a certain low energy scale. We show how this problem can be avoided by embedding massive gravity and its generalizations into higher dimensional theories.
I will discuss scalar-tensor models of gravity, which predict the spontaneous scalarization of neutron stars or/and black holes. In the cosmological setup, the scalar field responsible for scalarization is subject to a tachyonic instability during inflation as well as at other cosmological stages, depending on the model. The instability poses a problem for viability of such models. I will show...
Modified gravity theories are typically constructed in the Jordan frame, where the matter follows the geodesics of the metric. This is nothing more than a choice of field variable that leaves the observables intact. However recent developments in classical field theory revealed that fixing variables may affect how the fundamental assumptions in the theory building process are represented. For...
Weyl conformal geometry may play a role in early cosmology where effective theory at short distances becomes conformal. We consider the original Weyl gravity action, quadratic in the scalar curvature and in the Weyl tensor of Weyl conformal geometry; this action is invariant under Weyl scaling gauge transformations. In the absence of matter fields, we show that Weyl action has...
Global and local Weyl invariant theories can solve the hierarchy problem and generate all mass scales spontaneously, initiated by a dynamical process of “inertial spontaneous symmetry breaking” that does not involve a potential. I will discuss how inflation readily occurs in a scale invariant version of Starobinsky (R2) inflation and how an hierarchy of mass scales may be generated, stable...
Einstein gravity cannot be quantised using standard Quantum Field Theory techniques. Hence to describe gravity on quantum level then either a new, special quantisation prescription should be proposed or General Relativity should be replaced by another theory which can be properly quantised. If the first option is true, then General Relativity should possess an interacting UV fixed point (as an...
I will review flavor models based on non-Abelian discrete symmetries, motivated by neutrino oscillation data. I will discuss how CP violation, a necessary condition for baryogenesis, can be entirely group theoretical in origin in certain class of the non-Abelian discrete groups. I will then describe a proposal where successful baryogenesis can be achieved through flavon decays.
I will review the mechanism of cosmological relaxation of the electroweak scale and will discuss relaxion particle production during the evolution of the relaxion field, an effect which had been so far ignored in the relaxion literature. I will present its implications on the relaxion mechanism in general.
Over the past decades, the high-precision cosmological data have significantly improved our understanding of the Universe, contributing greatly to the establishment of the standard model of cosmology. However these results have also opened new questions in both fundamental physics and astrophysics. One of the great mystery of the universe is that more than 80% of the matter in our Universe is...
I will give a brief review of inflationary cosmology, including its motivation, observational status, the problem of initial conditions, and the string landscape scenario. I will also describe the problems with hilltop inflation and then I will show that the theory of alpha-attractors and D-brane inflation together can completely cover the range or values of n_s and r favored by Planck 2018.
The inflationary paradigm, already in its simplest disguises, has been spectacularly successful when it comes to agreement with observations. However, there’s a lot we do not yet know about inflation:
- what is its energy scale?
- how about its particle content?
- how did inflation begin?
…
New cosmological probes (at all scales, from CMB to interferometers) will soon put some of our best...
Tests of primordial non-Gaussianity (PNG) are a powerful tool to shed light on the physics of the Early Universe. Currently, the best limits on PNG come from Planck measurements of Cosmic Microwave Background (CMB) temperature and polarization anisotropies, which nearly saturated the CMB constraining power. After briefly reviewing current Planck PNG bounds for a variety of models, I will...
Multi-field inflation with curved field manifold attracts a lot of attention recently. From theoretical aspect, this class of models may be more naturally realized in the UV completion of inflation. From observational point of view, however, the current constraints on primordial non-Gaussianity and isocurvature perturbation already/marginally ruled out many of these models. In this talk I will...
We review quasi-single field inflation and the cosmological collider physics, emphasizing on recent progress. The cosmological collider is a model-independent way of extracting the mass and spin information of heavy particles at the energy scale of inflation. The same mechanism can also be used as a direct probe of the expansion history of the universe. After the introduction, we survey the...
How to model-independently distinguish the inflation scenario from alternatives to inflation is an important challenge in modern cosmology. In this talk, we show that massive fields in the primordial universe function as standard clocks and imprint clock signals in the density perturbations, which directly record the scale factor of the universe as a function of time, a(t). This function is...
We study the back-reaction of the infrared modes of an O(N) scalar theory in a classical de Sitter background. We use the nonperturbative renormalization group methods to extract analytically the flow of the Hubble constant as the gravitationally enhanced long wavelength modes are integrated out. For a massless theory, the interactions tend to renormalize negatively the Hubble constant, thus...
We show how a pair of field theory monodromies in which the shift symmetry is broken by small, well motivated deformations, naturally incorporates a mechanism for cancelling off radiative corrections to the cosmological constant. The lighter monodromy sector plays the role of inflation as well as providing a rigid degree of freedom that acts as a dynamical counterterm for the cosmological...
Cosmic inflation is a period of accelerated expansion in the Early Universe. Inflation is the most compelling proposal for the formation of of the observed structures in the Universe like galaxies and galactic clusters. It also makes the Universe uniform and spatially flat in agreement with observations. To drive inflation an exotic substance is needed, with pressure negative enough to cause...
A rigorous constraint analysis on inflationary cosmology entails several probes which collectively survey an extensive range of energy scales. We complement the current cosmic microwave background data with an updated compilation of the cosmic abundance limits of primordial black holes, with which we infer stringent constraints on the runnings of the scalar spectral index. The constraints on...
I will present the idea of combinig the constant roll inflation with the warm inflationary paradigm, which comes from the strong particle production during inflation. I will show how to solve such a system and I will rpesent fundamental applications of this theory: from inflation to primordial black holes production
We present a weakly nonlocal gravitational theory unitary and finite at quantum level in the quantum field theory framework. As a consequence of finiteness, there is no Weyl anomaly and the theory turns out to be conformal invariant at classical as well at quantum level. Therefore, nonlocal quantum gravity is a conformal invariant theory in the spontaneously broken phase of the Weyl symmetry....
We discuss scalar-tensor theories based on a non-Riemannian geometry, called the metric-affine geometry, where the metric and the connection are treated as independent variables. In the metric-affine formalism, the Einstein-Hilbert action enjoys an additional local symmetry, the projective symmetry, under a shift of the connection. We find that the projective symmetry can provide an...
Optical geometry is a spatial formalism for light propagation in Lorentzian spacetimes. This provides a geometrically interesting and useful framework for gravitational lensing, which is usually treated in terms of the quasi-Euclidean standard approximation instead. In this talk, I will first consider Riemannian optical geometry, and review basic results as well as recent work using the...
I discuss the prospects for constraining gravitational waves from non-minimal inflationary models using: (i) the large scale structure, through the so-called "fossil" signatures; (ii) cross-correlations of tracers of the large scale structure with secondary CMB anisotropies from kinetic and polarized Sunyaev–Zel'dovich effects. I show how these different routes for testing primordial...
In this talk, we show that there is a class of spacetime curvature singularities which can be resolved with metric and matter field transformations. As an example, we consider an anisotropic power-law inflation model with gauge and scalar fields in which a space-like curvature singularity exists at the beginning of time. First, we provide a transformation of the metric to the flat geometry....
We discuss how inflation can emerge from a four-fermion interaction induced by torsion. Inflation can arise from coupling torsion to Standard Model fermions, without any need of introducing new scalar particles beyond the Standard Model. Within this picture, the inflaton field can be a composite field of the SM-particles and arises from a Nambu-Jona-Lasinio mechanism in curved space-time,...
Primordial Black Holes (PBHs) are appealing candidates for dark matter in the universe but are severely constrained by theoretical and observational constraints. I will focus on the Hawking evaporation limits extended to Kerr Black Holes. These results have been obtained with a new to-be-published code entitled BlackHawk that I will briefly present. In particular, I will review the isotropic...
Many classical field models which "violate Lorentz symmetry" do so via a vector or tensor field which takes on a vacuum expectation value, thereby spontaneously breaking the underlying Lorentz symmetry of the Lagrangian. To obtain a tensor field with this behavior, one can posit a smooth potential for this field, or one can enforce a non-zero tensor value via a Lagrange multiplier. In this...
It is generally believed that modification of GR inevitably introduce extra physical degree(s) of freedom. In this talk I argue that this is not the case by constructing modified gravity theories with two local physical degrees of freedom. After classifying such theories into two types, I show explicit examples and discuss their cosmology and phenomenology.
We will discuss in our talk a picture for blackholes' inner structure and microscopic state in which matters falling into the horizon or consisting of them are oscillating around instead of accumulating statically on their central point, thus resolving the Schwarzschild singularity naturally. After quantizing, this picture not only blurs the horizon remarkably, but also provides an...
The presence of a large, non-vanishing background charge in the universe can interestingly have implications on symmetry restoration at high temperature. In theories with continuous global symmetries, like the R-symmetry of the MSSM, these can lead to important cosmological effects seemingly independent of the short-distance scale physics. Here we explore the effect of temporary R-symmetry...
We connect the electroweak (EW) baryogenesis and the dark matter physics in a complex singlet scalar S extension of the Standard Model. We impose the additional CP and Z_2 symmetries on the scalar potential. With the complex vacuum expectation value of S at the temperature higher than the EW phase transition, the CP symmetry is spontaneously broken and a strong first-order EW phase transition...
Smooth QG is the attempt to use findings and infinite geometric constructions of differential geometry and topology in dimensions 3 and 4, to solve problems in physics, especially gravitational physics. The relation between general relativity and quantum mechanics is of particular interest. We report the recent result of G. Etesi that large exotic R4's are Ricci-flat and Koehler so that they...
In this talk, I investigate the new mathematical approximation for the equation of state of unified dark matter and dark energy. This approximation provides well-behaving evolution of state for both small and high redshifts. In particular, the dark fluid composed by dark matter and dark energy described by our approximation behaves like dark matter for big redshifts and like dark energy at...
In this talk, we present a complete analysis of the quantization of the classical Brans-Dicke theory using the method of affine quantization in the Hamiltonian description of the theory. The affine quantization method is based on the symmetry of the phase space of the system, in this case the (positive) half-plane, which is identified with the affine group. We consider a...
Teleparallel gravity is an alternative, but equivalent (in field equations) to General Relativity description of gravitational interactions where gravity is mediated through torsion instead of curvature. Horndeski gravity is the most general scalar-tensor theory, with a single scalar field, leading to second-order field equations and after the GW170817 it has been severely constrained. In this...
Understanding the laws of inflation can shed light on the processes that govern physics at very high energy scales, beyond current experimental limits. In particular, the characterisation and detection of primordial gravitational waves produced during inflation can be an excellent test for the particle content of the very early universe. We consider an inflationary realisation whose tensor...
Understanding the laws of inflation can shed light on the processes that govern physics at very high energy scales, beyond current experimental limits. In particular, the characterisation and detection of primordial gravitational waves produced during inflation can be an excellent test for the particle content of the very early universe. We consider an inflationary realisation whose tensor...
It is well-known that there are problems with the standard model of cosmology that hint at possible physics beyond the $\Lambda$CDM paradigm. In particular, the 4$\sigma$ tension in the values of $H_0$ coming from CMB and supernovae measurements is motivation enough to consider alternative cosmological models.
In this talk, I will introduce one such model, the interacting vacuum scenario....
We study the Λ(α)CDM models with Λ(α) being a function of the time-varying fine structure constant α. We give a close look at the constraints on two specific Λ(α)CDM models with one and two model parameters, respectively, based on the cosmological observational measurements along with 313 data points for the time-varying α. We find that the model parameters are constrained to be around 10^−4,...
Despite the good agreement between theoretical predictions and observational results, the cosmological constant is not a satisfactory explanation for the accelerated expansion of the universe. Hence an intense theoretical effort has been devoted to the study of models beyond General Relativity plus a cosmological constant.
In this talk, I will present ongoing work on the study of the...
Particle decay processes in the early Universe have deep and profound implications in cosmology. In a regime where curvature cannot be neglected anymore, the Minkowskian quantum field theory is ultimately only an approximation and of limited applicability. Because the energy conservation law is violated, the particle decay rates, cross sections and lifetimes are modified compared to usual flat...
Gravitational Waves through the binary formation in Merging Galaxies
Authors: Rajesh Kumar Dubey and Shankar Pathak
Affiliation: Lovely Professional University, Punjab, India
Gravitational waves: Violent events, such as the collision of two black holes, are thought to be able to create ripples in space-time known as gravitational waves. In 2016, the Laser Interferometer Gravitational-Wave...
The cosmology of modified teleparallel gravity theories, such as $f(T)$ or scalar-torsion gravity, is a widely studied field. Most often one considers flat ($k = 0$) cosmology, while the non-flat case ($k = \pm 1$) is less well studied. While in the former it is easy to find a combination of tetrad and spin connection that solves the antisymmetric part of the field equations, thus leaving only...
We study a model of the emergent dark universe, which lives on the time-like hypersurface in a five-dimensional bulk spacetime. The holographic fluid is assumed to play the role of the dark sector, mainly including the dark energy and apparent dark matter. Based on the modified Friedmann equations, we present a Markov-Chain-Monte-Carlo analysis with the observational data, including type Ia...
In this talk we construct new exact solutions in Einstein-Gauss-Bonnet and Lovelock gravity, describing asymptotically flat black strings. The solutions exist also under the inclusion of a cosmological term in the action, and are supported by scalar fields with finite energy density, which are linear along the extended direction and have kinetic terms constructed out from Lovelock tensors. The...
Einstein's theory of gravity (general relativity, GR) is based on Riemannian geometry. Modified theories of gravity such as f(R) theories are also based on Riemann spaces and so are intrinsically limited. In order to better understand the nature of gravity it is worth going further, beyond Riemannian geometry. The simplest extensions of Riemannian geometry are based on non-null non-metricity...
arXiv:1904.02458v1 [astro-ph.CO]
In this paper we study implications of the possible excess of 21-cm line global signal at the epoch of cosmic dawn on the evolutions of a class of dynamically interacting dark energy (IDE) models. We firstly summarize two dynamical mechanisms in which different background evolutions can exert considerable effects on the 21-cm line global signal. One is the...
We use the quasinormal modes of a massless scalar perturbation to probe the phase transition of the high dimension charged AdS black holes. As a result, the signature of the critical behavior of this black hole solution is detected [ [1] , [2] ]. As an alternative, we can use also the unstable circular photon orbits around a $RN-AdS_4$ BH in massive gravity to establish a direct link between...
In this talk, I will discuss the key imprints of the most general scalar tensor theories at stellar scales, and explain how solar observations can significantly improve previous constraints on their theory space. Finally, I will discuss the relevant consequences at cosmological scales.
I will discuss a new mechanism of producing superheavy fields (with the masses much larger than the inflationary Hubble rate) during inflation. The key ingredient of the mechanism is a linear coupling of the superheavy field to a function of the inflaton. During inflation this induces almost constant force dragging the corresponding field to the non-zero value. I will discuss implications of...
Thermal freeze-out or freeze-in during a period of early matter domination can give rise to the correct dark matter abundance for an annihilation rate of $\big<\sigma_{ann}v\big>_f < 3 \times 10^{−26} {\rm cm}^3 {\rm s}^{−1}$. In the standard scenario, a single field that behaves like matter drives the early matter dominated era and decays to radiation before big bang nucleosynthesis. However,...
To gauge fix, or not to gauge fix: that is the question I address in my talk. The covariant formulation of teleparallel gravity theories must be formulated with a spin connection. However, one can always choose a gauge which puts the spin connection to zero. This is not always preferred, though it definitely makes the Hamiltonian analysis easier. There are two ways to avoid gauge fixing. One...
I will discuss preheating in multi-field models of inflation with a curved field-space manifold. In the case of two-field generalizations of $\alpha$-attractor models with is a highly curved hyperbolic field-space manifold, analytical progress can be made for preheating using the WKB approximation and Floquet analysis. I will show the emergence of a simple scaling behavior of the Floquet...
In generic higher-order scalar-tensor theories which avoid the Ostrogradsky instability, the presence of a scalar field significantly modifies the propagation of matter perturbations, even in weakly curved backgrounds. This affects notably the speed of sound in the atmosphere of the Earth. It can also generate instabilities in homogeneous media. I will use this to constrain the viable...
We propose a novel mechanism for the production of gravitational waves in the early Universe that originates from the relaxation processes induced by the QCD phase transition. While the energy density of the quark-gluon mean-field is monotonously decaying in real time, its pressure undergoes a series of violent oscillations at the characteristic QCD time scales that generates a primordial...
Bigravity is an extension of dRGT (de Rham, Gabadadze, Tolley) massive gravity, which arises by having two dynamical metric tensors. Massive gravity has recently had a flurry of interest in the last decade due to the self-accelerating properties of a massive graviton, leading to possible solutions for dark energy. Bigravity has been studied as an alternative dark energy model due to the lack...
