arXiv subjects

Girish Kumar Chakravarty

Publications and source records attributed to Girish Kumar Chakravarty.

10 recordsLinked to original sources

arXiv2020

Inflation, reheating, leptogenesis and bounds on soft supersymmetry breaking parameters

In the no-scale supergravity with Type-I Seesaw model of Non-minimal supersymmetric standard model (NMSSM), we have analysed inflation, reheating and leptogenesis. A no-scale supergravity realization of Starobinsky model of inflation in simple Wess-Zumino model have been shown earlier by Ellis et al. Here we show a no-scale supergravity realization of Starobinsky model of inflation in Type-I Seesaw framework of NMSSM. In this framework an appropriate choice of no-scale Kähler potential results in Starobinsky like plateau inflation along a Higgs-sneutrino $D$-flat direction consistent with the CMB observations. In leptogenesis, the soft-breaking trilinear and bilinear terms play important role. Using conditions for non-thermal contribution to $CP$ asymmetry and successful leptogenesis together with the appropriate reheating at the end of inflation, we have obtained important constraints on the soft supersymmetry breaking parameters.

hep-ph↗

arXiv2020

Supergravity Model of Inflation and Explaining IceCube HESE Data via PeV Dark Matter Decay

We construct an unified model of inflation and PeV dark matter with an appropriate choice of no-scale Kähler potential, superpotential and gauge kinetic function in terms of MSSM fields and hidden sector Polonyi field. The model is consistent with the CMB observations and can explain the PeV neutrino flux observed at IceCube HESE. A Starobinsky like Higgs-sneutrino plateau inflation is obtained from the $D$-term SUGRA potential while $F$-term being subdominant during inflation. To get PeV dark matter, SUSY breaking at PeV scale is achieved through Polonyi field. This sets the scale for soft SUSY breaking parameters $m_0, m_{1/2}, A_0 $ at the GUT scale in terms of the parameters of the model. The low energy particles spectrum is obtained by running the RGEs. We show that the $\sim$125 GeV higgs and the gauge coupling unification can be obtained in this model. The $6$ PeV bino-type dark matter is a subdominant fraction ($\sim 11\%$) of the relic density and its decay gives the PeV scale neutrino flux observed at IceCube by appropriately choosing the couplings of the $R$-parity violating operators. Also we find that there is a degeneracy in scalar field parameters $(γ, β)$ and coupling $ζ$ value in producing the correct amplitude of CMB power spectrum. However the value of parameter $\tan(β)=1.8$, which is tightly fixed from the requirement of PeV scale SUSY breaking, removes the degeneracy in the values of the scalar field parameters to provide a unique solution for inflation. In this way it brings the explanation for dark matter, PeV neutrinos and inflation within the same framework.

hep-ph↗

arXiv2018

Constraints on Born-Infeld gravity from the speed of gravitational waves after GW170817 and GRB 170817A

The observations of gravitational waves from the binary neutron star merger event GW170817 and the subsequent observation of its electromagnetic counterparts from the gamma-ray burst GRB 170817A provide us a significant opportunity to study theories of gravity beyond general relativity. An important outcome of these observations is that they constrain the difference between the speed of gravity and the speed of light to less than $10^{-15}c$. Also, the time delay between the arrivals of gravitational waves at different detectors constrains the speed of gravity at the Earth to be in the range $0.55c < v_{gw} < 1.42c$. We use these results to constrain a widely studied modified theory of gravity: Eddington-inspired Born-Infeld (EiBI) gravity. We show that, in EiBI theory, the speed of gravitational waves in matter deviates from $c$. From the time delay in arrival of gravitational wave signals at Earth-based detectors, we obtain the bound on the theory parameter $κ$ as $\vertκ\vert \lesssim 10^{21}\, m^2$. Similarly, from the time delay between the signals of GW170817 and GRB 170817A, in a background Friedmann-Robertson-Walker universe, we obtain $\vert κ\vert \lesssim 10^{37}\, m^2$. Although the bounds on $κ$ are weak compared to other earlier bounds from the study of neutron stars, stellar evolution, primordial nucleosynthesis, etc., our bounds are from the direct observations and thus worth noting.

gr-qc↗

arXiv2017

Resurrecting Quartic and Quadratic inflaton potentials in two-field inflationary model

After the release of the PLANCK data, it is evident that inflationary paradigm has stood the test of time. Even though, it is difficult to realise inflationary paradigm in a particle physics model as the present observations have ruled out the simplest quartic and quadratic inflationary potentials, which generically arise in particle physics. We would show that such simplest inflationary potentials can evade discrepancies with observations, if the inflaton field is assisted by another scalar during inflation. Moreover, unlike other multifield models, our model yields no isocurvature perturbations and negligible non-Gaussianity, making it more compatible with the present data. Above all, our model can also be realised in the framework of SUGRA.

astro-ph.CO↗

arXiv2017

Constraints on cosmological viscosity and self interacting dark matter from gravitational wave observations

It has been shown that gravitational waves propagate through ideal fluids without experiencing any dispersion or dissipation. However, if the medium has a non-zero shear viscosity $η$ , gravitational waves will be dissipated at a rate proportional to $G \,η$. We constrain dark matter and dark energy models with non-zero shear viscosity by calculating the dissipation of gravitational waves from GW150914 which propagate over a distance of $410\, $ Mpc through the dissipative fluid and comparing the data with the theoretical prediction. This provides a proof-of-principle demonstration of the fact that future observations gravitational waves at LIGO have the potential of better constraining the viscosity of dark matter and dark energy.

hep-ph↗

arXiv2016

Plateau Inflation in $R$-parity Violating MSSM

Inflation with plateau potentials give the best fit to the CMB observables as they predict tensor to scalar ratio stringently bounded by the observations from Planck and BICEP2/Keck. In supergravity models it is possible to obtain plateau potentials for scalar fields in the Einstein frame which can serve as the inflation potential by considering higher dimensional Planck suppressed operators and by the choice of non-canonical Kähler potentials. We construct a plateau inflation model in MSSM where the inflation occurs along a sneutrino-Higgs flat direction. A hidden sector Polonyi field is used for the breaking of supersymmetry after the end of the inflation. The proper choice of superpotential leads to strong stabilization of the Polonyi field, $m_{Z}^2\gg m_{3/2}^2$, which is required to solve the cosmological moduli problem. Also, the SUSY breaking results in a TeV scale gravitino mass and scalar masses and gives rise to bilinear and triliear couplings of scalars which can be tested at the LHC. The sneutrino inflation field can be observed at the LHC as a TeV scale diphoton resonance like the one reported by CMS and ATLAS.

hep-ph↗

arXiv2016

Dilaton assisted two-field inflation from no-scale supergravity

We present a two-field inflation model where inflaton field has a non-canonical kinetic term due to the presence of a dilaton field. It is a two-parameter generalization of one-parameter Brans-Dicke gravity in the Einstein frame. We show that in such an inflation model the quartic and quadratic inflaton potentials, which are otherwise ruled out by the present Planck-{\it Keck}/BICEP2 data, yield scalar spectral index and tensor-to-scalar ratio in accordance with the present data. Such a model yield tensor-to-scalar ratio of the order of $10^{-2}$ which is within the reach of $B-$mode experiments like {\it Keck}/BICEP3, CMBPol and thus can be put to test in the near future. This model yields negligible non-Gaussianity and no isocurvature perturbations upto slow-roll approximation. Finally, we show that such a model can be realised in the realm of no-scale supergravity.

hep-ph↗

arXiv2016

Testing theories of Gravity and Supergravity with inflation and observations of the cosmic microwave background

Many extensions of Einstein's theory of gravity have been studied and proposed with various motivations like the quest for a quantum theory of gravity to extensions of anomalies in observations at the solar system, galactic and cosmological scales. These extensions include adding higher powers of Ricci curvature $R$, coupling the Ricci curvature with scalar fields and generalized functions of $R$. In addition when viewed from the perspective of Supergravity (SUGRA) many of these theories may originate from the same SUGRA theory interpreted in different frames. SUGRA therefore serves as a good framework for organizing and generalizing theories of gravity beyond General Relativity. All these theories when applied to inflation (a rapid expansion of early Universe in which primordial gravitational waves might be generated and might still be detectable by the imprint they left or by the ripples that persist today) can have distinct signatures in the Cosmic Microwave Background radiation temperature and polarization anisotropies. In this review we give a detailed discussion on the standard model of cosmology ($Λ$CDM), inflation and cosmological perturbation theory. We survey the theories of gravity beyond Einstein's General Relativity, specially which arise from SUGRA, and study the consequences of these theories in the context of inflation and put bounds on the theories and the parameters therein from the observational experiments like Planck, Keck/BICEP. The possibility of testing these theories in the near future in CMB observations and new data coming from colliders like the LHC, provides an unique opportunity for constructing verifiable models of particle physics and General Relativity.

astro-ph.CO↗

arXiv2016

Plateau Inflation in SUGRA-MSSM

We explored a Higgs inflationary scenario in the SUGRA embedding of the MSSM in Einstein frame where the inflaton is contained in the $SU(2)$ Higgs doublet. We include all higher order non-renormalizable terms to the MSSM superpotential and an appropriate Kähler potential which can provide slow-roll inflaton potential in the $D-$flat direction. In this model, a plateau-like inflation potential can be obtained if the imaginary part of the neutral Higgs acts as the inflaton. The inflationary predictions of this model are consistent with the latest CMB observations. The model represents a successful Higgs inflation scenario in the context of Supergravity and it is compatible with Minimal Supersymmetric extension of the Standard Model.

hep-ph↗

arXiv2015

Power law Starobinsky model of inflation from no-scale SUGRA

We consider a power law $\frac{1}{M^2}R^β$ correction to Einstein gravity as a model of inflation. The interesting feature of this form of generalization is that small deviations from the Starobinsky limit $β=2$ can change the value of tensor to scalar ratio from $r \sim \mathcal{O}(10^{-3})$ to $r\sim \mathcal{O}(0.1)$. We find that in order to get large tensor perturbation $r\approx 0.1$ as indicated by BKP measurements, we require the value of $β\approx 1.83$ thereby breaking global Weyl symmetry. We show that the general $R^β$ model can be obtained from a SUGRA construction by adding a power law $(Φ+\bar Φ)^n$ term to the minimal no-scale SUGRA Kähler potential. We further show that this two parameter power law generalization of the Starobinsky model is equivalent to generalized non-minimal curvature coupled models with quantum corrected $Φ^{4}$- potentials i.e. models of the form $ξΦ^{a} R^{b} + λΦ^{4(1+γ)}$ and thus the power law Starobinsky model is the most economical parametrization of such models.

hep-ph↗