arXiv subjects

Debaprasad Maity

Publications and source records attributed to Debaprasad Maity.

At least 91 records · Page 5Linked to original sources

arXiv2015

Kinetic gravity braiding and natural inflation in the light of BICEP2 and PLANCK

Based on our previous work, we constructed a phenomenological model of inflation with the higher derivative axion field in the light of recent cosmological expertiments BICEP2 and PLANCK. In order to achieve observed values for the important cosmological parameters $(n_s,r)$ we employ higher derivative kinetic term called kinetic gravity braiding (KGB) for the axion in compatible with the constant shift symmetry. Phenomenologically we choose a particular form of the braiding function $M(ϕ)$ which correctly reproduces the observed value of $(n_s, r)$ based on the recent cosmological observations. Furthermore we also find axion decay constant $f$ and the scale of inflation $Λ$ to be naturally sub-Planckian consistent with the reheating after the end of inflation. Within the sufficient number of e-folding ${\cal N}$, we also find sub-Planckian field excursion for the axion field $Δϕ\simeq f$.

hep-th↗

arXiv2015

Modified natural inflation: A small single field model with a large tensor to scalar ratio

In this paper we explored in detail a phenomenological model of modified single field natural inflation in light of recent cosmological experiments, BICEP2. Our main goal is to construct an inflationary model which not only predicts the important cosmological quantities such as $(n_s, r)$ compatible with experimental observation, but also is consistent with the low energy effective theory framework. Therefore, all the fundamental scale apart from $M_p$ and quantities of our interest should be within the sub-Planckian region. In order to achieve our goal we modify the usual single field natural inflationary model by a specific form of higher derivative kinetic term called kinetic gravity braiding (KGB). One of our guiding principles to construct such a model is the constant shift symmetry of the axion. We have chosen the form of the KGB term in such a way that it predicts the required value of $n_s\simeq 0.96$ and a large tensor to scalar ratio $r> 0.1$. Importantly for a wide range of parameter space our model has sub-Planckian axion decay constant $f$ and the scale of inflation $Λ$. However, the reheating after the end of inflation limits the value of $f$ so that we are unable to get $f$ to be significantly lower than $M_p$. Furthermore, we find sub-Planckian field excursion for the axion field $Δϕ\simeq f$ for the sufficient number of e-folding ${\cal N} \gtrsim 50 $. We also discussed in detail about the natural preheating mechanism in our model based on the recently proposed Chern-Simon coupling. We found this gravity mediated preheating is very difficult to achieve in our model. With our general analytic argument, we also would like to emphasize that Chern-Simons mediated preheating is very unlikely to happen in any slow roll inflationary model.

hep-th↗

arXiv2014

Novel Parity Violating Transport Coefficients in 2+1 Dimensions from Holography

We construct a 3+1 dimensional holographic model dual to a parity violating hydrodynamic system in 2+1 dimensions. Our model contains gravitational and electrodynamic Chern-Simons terms coupled to a neutral pseudo scalar $θ$, and a potential composed of quadratic and quartic terms in $θ$. The background is a charged black brane. We study the hydrodynamics to first order in spacetime derivatives near the probe limit of the pseudo scalar, by extracting the transport coefficients from the scalar, vector, and tensor modes of bulk perturbations. We study two mechanisms for breaking the parity of the boundary fluid: the parity is either spontaneously broken by the nonzero vev of the dual pseudo scalar operator, or by the pseudo scalar source on the boundary. The resulting transport coefficients have unusual behaviors compared to those in ordinary materials.

hep-th↗

arXiv2013

Kinetic Gravity Braiding and axion inflation

We constructed a new class of inflationary model with the higher derivative axion field which obeys constant shift symmetry. In the usual axion (natural) inflation, the axion decay constant is predicted to be in the super-Planckian regime which is believed to be incompatible with an effective field theory framework. With a novel mechanism originating from a higher derivative kinetic gravity braiding (KGB) of an axion field we found that there exist a huge parameter regime in our model where axion decay constant could be naturally sub-Planckian. Thanks to the KGB which effectively reduces the Planck constant. This effectively reduced Planck scale provides us the mechanism of further lowering down the speed of an axion field rolling down its potential without introducing super-Planckian axion decay constant. We also find that with that wide range of parameter values, our model induces almost scale invariant power spectrum as observed in CMB experiments.

hep-th↗

arXiv2012

Semi-realistic Bouncing Domain Wall Cosmology

In this paper we constructed a semi-realistic cosmological model in a dynamic domain wall framework. Our universe is considered to be a (3+1) dimensional dynamic domain wall in a higher dimensional Einstein-Maxwell-Born-Infeld background. One of our interesting outcomes from the effective Hubble equation for the domain wall dynamics is that it contains an additional component of "dark matter" which is induced from the charge of the bulk Born-Infeld gauge field. In this background spacetime we have studied the cosmological dynamics of the domain wall. In addition to the Born-Infield gauge field if we consider additional pure gauge field, a non-singular bounce happens at the early stage with a smooth transition between contracting and expanding phase.

gr-qc↗

arXiv2012

A Holographic Model For Hall Viscosity

We have modified the holographic model of Saremi and Son by using a charged black brane, instead of a neutral one, such that when the bulk pseudo scalar potential is made of quadratic and quartic terms, parity can still be broken spontaneously in the boundary theory. In our model, the 3+1 dimensional bulk has a pseudo scalar coupled to the gravitational Chern-Simons term in the anti de Sitter charged black brane back ground. Parity could be broken spontaneously in the bulk by the pseudo scalar hairy solution and give rise to non-zero Hall viscosity at the boundary theory.

hep-th↗

arXiv2012

The role of higher derivative bulk scalar in stabilizing a warped spacetime

The backreaction on the Randall-Sundrum warped spacetime is determined in presence of scalar field in the bulk. A general analysis shows that the stability of such a model can be achieved only if the scalar field action has non-canonical higher derivative terms. It is further shown that the gauge hierarchy problem can be resolved in such a stabilized scenario by appropriate choice of various parameters of the theory. The effective cosmological constant on the brane is shown to vanish.

hep-th↗

arXiv2012

Analysing the Effect on CMB in a Parity and Charge Parity Violating Varying Alpha Theory

In this paper we study in detail the effect of our recently proposed model of parity and charge-parity (PCP) violating varying alpha on the Cosmic Microwave Background (CMB) photon passing through the intra galaxy-cluster medium (ICM). The ICM is well known to be composed of magnetized plasma. According to our model, the polarization and intensity of the CMB would be affected when traversing through the ICM due to non-trivial scalar photon interactions. We have calculated the evolution of such polarization and intensity collectively, known as the stokes parameters of the CMB photon during its journey through the ICM and tested our results against the Sunyaev-Zel'dovich (SZ) measurement on Coma galaxy cluster. Our model contains a PCP violating parameter, $β$, and a scale of alpha variation $ω$. Using the derived constrained on the photon-to-scalar conversion probability, ${\bar P}_{γ\rightarrow ϕ}$, for Coma cluster in ref.[34] we found a contour plot in the ($ω,β$) parameter plane. The $β=0$ line in this parameter space corresponds to well-studied Maxwell-dilaton type models which has lower bound on $ω\gtrapprox 6.4 \times 10^{9}$ GeV. In general, as the absolute value of $β$ increases, lower bound on $ω$ also increases. Our model in general predicts the modification of the CMB polarization with a non-trivial dependence on the parity violating coupling parameter $β$. However, it is unconstrained in this particular study. We show that this effect can in principle be detected in the future measurements on CMB polarization such that $β$ can also be constrained.

astro-ph.CO↗

arXiv2011

Constraining PCP Violating Varying Alpha Theory Through Laboratory Experiments

In this report we have studied the implication of a parity and charge-parity (PCP) violating interaction in varying alpha theory. Due to this interaction, the state of photon polarization can change when it passes through a strong background magnetic field. We have calculated the optical rotation and ellipticity of the plane of polarization of an electromagnetic wave and tested our results against different laboratory experiments. Our model contains a PCP violating parameter $β$ and a scale of alpha variation $ω$. By analyzing the laboratory experimental data, we found the most stringent constraints on our model parameters to be $1\leq ω\leq 10^{13} GeV^2$ and $-0.5\leq β\leq 0.5$. We also found that with the existing experimental input parameters it is very difficult to detect the ellipticity in the near future.

hep-ph↗

arXiv2011

Holographic Multi-Band Superconductor

We propose a gravity dual for the holographic superconductor with multi-band carriers. Moreover, the currents of these carriers are unified under a global flavored SO(3) symmetry, which is dual to the bulk SO(3) gauge symmetry. We study the phase diagram of our model, and find it qualitatively agrees with the one for the realistic 2-band superconductor, such as $MgB_2$. We also identify the bulk field dual to the electromagnetic $U(1)_{EM}$ current, which should be invariant under the global flavored SO(3) rotation. We then evaluate the corresponding holographic conductivity and find the expected mean field like behaviors.

hep-th↗

arXiv2011

$d+id$ Holographic Superconductors

A holographic model of $d+id$ superconductors based on the action proposed by Benini, Herzog, and Yarom [arXiv:1006.0731] is studied. This model has a charged spin two field in an AdS black hole spacetime. Working in the probe limit, the normalizable solution of the spin two field in the bulk gives rise to a $d+id$ superconducting order parameter at the boundary of the AdS. We calculate the fermion spectral function in this\ superconducting background and confirm the existence of fermi arcs for non-vanishing Majorana couplings. By changing the relative strength $γ$ of the $d$ and $id$ condensations, the position and the size of the fermi arcs are changed. When $γ=1$, the spectrum becomes isotropic and the spectral function is s-wave like. By changing the fermion mass, the fermi momentum is changed. We also calculate the conductivity for these holographic $d+id$ superconductors where time reversal symmetry has been broken spontaneously. A non-vanishing Hall conductivity is obtained even without an external magnetic field.

hep-th↗

arXiv2011

Higgs Inflation in Horava-Lifshitz Gravity

We study the possibility of standard model Higgs boson acting as an inflaton field in the framework of Horava-Lifshitz Gravity. Under this framework, we showed that it is possible for the Higgs field to produce right amount of inflation and generate scale invariant power spectrum with the correct experimental value. Thanks to the foliation preserving diffeomorphism and anisotropic space-time scaling, it essentially helps us to construct this model without the pre-existing inconsistency coming from cosmological and particle physics constraints. We do not need to introduce any non-minimal or higher derivative coupling term in an arbitrary basis either.

hep-th↗

arXiv2011

Cosmological Behavior of a Parity and Charge-Parity Violating Varying Alpha Theory

In this report we construct a phenomenological model in which the time variation of the fine structure constant, $α$, is induced by a parity and charge-parity (PCP) violating interaction. Such a PCP violation in the photon sector has a distinct physical origin from that in the conventional models of this kind. We calculate the cosmological birefringence so induced in our model and show that it in turn produces a new non-vanishing multipole moment correlation between the temperature and the polarization anisotropies in the CMB spectrum. We have also calculated the amount of optical rotation due to a strong background magnetic field and the effect of our new PCP violating term on the variation of $α$ during the cosmic evolution. We found that only in the radiation dominated era can the contribution of the new PCP violating term to the variation of $α$ be non-vanishing.

hep-th↗

arXiv2010

Properties of CFTs dual to Charged BTZ black-hole

We study properties of strongly coupled CFT's with non-zero background electric charge in 1+1 dimensions by studying the dual gravity theory - which is a charged BTZ black hole. Correlators of operators dual to scalars, gauge fields and fermions are studied at both T=0 and $T\neq 0$. In the $T=0$ case we are also able to compare with analytical results based on $ AdS_2$ and find reasonable agreement. In particular the correlation between log periodicity and the presence of finite spectral density of gapless modes is seen. The real part of the conductivity (given by the current-current correlator) also vanishes as $ω\rightarrow 0$ as expected. The fermion Green's function shows quasiparticle peaks with approximately linear dispersion but the detailed structure is neither Fermi liquid nor Luttinger liquid and bears some similarity to a "Fermi-Luttinger" liquid. This is expected since there is a background charge and the theory is not Lorentz or scale invariant. A boundary action that produces the observed non-Luttinger-liquid like behavior ($k$-independent non-analyticity at $ω=0$) in the Greens function is discussed.

hep-th↗

arXiv2010

Towards A Holographic Model of D-Wave Superconductors

The holographic model for S-wave high T_c superconductors developed by Hartnoll, Herzog and Horowitz is generalized to describe D-wave superconductors. The 3+1 dimensional gravitational theory consists a symmetric, traceless second-rank tensor field and a U(1) gauge field in the background of the AdS black hole. Below T_c the tensor field which carries the U(1) charge undergoes the Higgs mechanism and breaks the U(1) symmetry of the boundary theory spontaneously. The phase transition characterized by the D-wave condensate is second order with the mean field critical exponent beta = 1/2. As expected, the AC conductivity is isotropic below T_c and the system becomes superconducting in the DC limit but has no hard gap.

hep-th↗

arXiv2008

Dynamic domain walls in Maxwell-Dilaton background

Motivated by the well know Chamblin-Reall solutions of $n$-dimensional background spacetime in a dilaton gravity and the dynamics of a domain wall in the same backgrounds, we have tried to generalize those solutions by including electromagnetic field in the bulk. The electromagnetic field is assumed to be coupled with the scalar field in an exponential way. Under the specific relations among the various parameters in our model, we have found five different types of solutions. For every case, the solution has singularity. In these backgrounds, we have also studied the dynamics of domain wall. The energy densities which play the role of these interesting dynamics, are know to be induced from the bulk fields through Israel junction condition. In this more general background field configuration, we have again found many occasions to exist static bulk spactime consistent with the dynamic domain wall. In several cases, depending upon the values of the parameters, in the early stage of evolution, the domain wall is found to have an inflationary phase for finite period of it's proper time followed by usual decelerated expansion.

hep-th↗

arXiv2008

Domain walls in Born-Infeld-dilaton background

We study the dynamics of domain walls in Einstein-Born-Infeld-dilaton theory. Dilaton is non-trivially coupled with the Born-Infeld electromagnetic field. We find three different types of solutions consistent with the dynamic domain walls. For every case, the solutions have singularity. Further more, in these backgrounds, we study the dynamics of domain walls. We qualitatively plot various form of the bulk metrics and the potential encountered by the domain walls. In many cases, depending upon the value of the parameters, the domain walls show bouncing universe and also undergo inflationary phase followed by standard decelerated expansion.

hep-th↗

arXiv2008

Cosmological constant, brane tension and large hierarchy in a generalized Randall-Sundrum braneworld scenario

We consider a generalized Randall Sundrum (RS) brane world scenario with a cosmological constant $Ω$ induced on the visible brane. We show that for $Ω<0$, resolution of the hierarchy problem requires an upper bound on the magnitude of $Ω$. The corresponding tension on the visible brane can be positive or negative. On the other hand, there is no such bound for $Ω>0$. However, in this case, the resolution of the hierarchy problem along with the tuning of the value of the cosmological constant to its observed value closed to $+10^{-124}$ (in Planck units) naturally lead to the tuning of the modulus to a small value of inverse Planck length as estimated in the original RS scenario.

hep-th↗