arXiv subjects

Neven Bilic

Publications and source records attributed to Neven Bilic.

At least 19 recordsLinked to original sources

arXiv2023

Constant-roll inflation with tachyon field in the holographic braneworld

We study inflation driven by the tachyon field in the holographic braneworld by assuming the second slow-roll parameter $\eta$ is constant. The parameter $\eta$ can be either defined by the tachyon scalar field and the Hubble parameter or by the Hubble parameter only. By assuming a constant $\eta$, we derive and numerically solve a differential equation for the Hubble expansion rate. We calculate numerically the scalar spectral index and the tensor-to-scalar ratio. We confront the results with the observational data and find some constraints on the free model parameters. The swampland conjectures are discussed in the context of the constant-roll inflation, with some accent on the holographic model.

gr-qc↗

arXiv2023

Tachyon constant-roll inflation in Randall-Sundrum II cosmology

We study inflation in a model with constant second slow-roll parameter $\eta$. In this case, the Hubble expansion rate equation has analytical solutions describing four possible, nontrivial inflation scenarios. The evolution of the inflaton governed by a tachyon field is studied in the framework of the standard and Randall-Sundrum II cosmology. The attractor behavior of the solution is briefly demonstrated. Finally, the calculated values of the parameters $n_{\rm s}$ and $r$ are compared with observational data.

gr-qc↗

arXiv2022

Thermodynamics of AdS planar black holes and holography

A large AdS Schwarzschild black hole can be approximated by an AdS planar black hole. However, the temperature of a planar black hole is not well defined due to the translational invariance of the horizon. We propose to fix this arbitrariness by imposing the entropy area law. Furthermore, using the AdS/CFT holography, we propose a relationship between the temperatures of an AdS planar and large AdS Schwarzschild black holes.

hep-th↗

arXiv2022

Primordial perturbations and inflation in a holography inspired Gauss-Bonnet cosmology

We consider an action for gravity that, in addition to the Einstein-Hilbert term, contains a function of the Ricci scalar and the Gauss-Bonnet invariant. The specific form of the function considered is motivated by holographic cosmology. At background level the field equations imply modified Friedmann equations of the same form as those in the holographic cosmology. We calculate the cosmological perturbations and derive the corresponding power spectra assuming a general $k$-inflation. We find that the resulting power spectra differ substantially from those obtained in both holographic and standard cosmology. The estimated spectral index and tensor-to-scalar ratio are confronted with the Planck results.

gr-qc↗

arXiv2021

Analog Schwarzschild-like geometry in fluids with external pressure

We study acoustic geometry in fluids with external pressure. In particular, we examine the conditions under which the acoustic metric mimics a Schwarzschild-like metric. We demonstrate that it is possible to mimic a Schwarzschild-like geometry in a consistent way only in the framework of relativistic acoustic geometry.

gr-qc↗

arXiv2020

Primordial perturbations and inflation in holographic cosmology

We consider an inflationary scenario in the holographic braneworld with a cosmological fluid occupying the 3+1 dimensional brane located at the holographic boundary of an asymptotic ADS$_5$ bulk. The contribution of the boundary conformal field can be represented as a modification of Einstein's equations on the boundary. Using these effective Einstein equations we calculate the cosmological perturbations and derive the corresponding power spectra assuming a general $k$-essence type of inflaton. We find that the braneworld scenario affects the scalar power spectrum only in the speed of sound dependence on the slow-roll parameters whereas there is no change in the tensor power spectrum. This implies that the changes in the spectral indices appear at the second order in the slow-roll parameter expansion.

gr-qc↗

arXiv2019

Tachyon inflation in the holographic braneworld

A model of tachyon inflation is proposed in the framework of holographic cosmology. The model is based on a holographic braneworld scenario with a D3-brane located at the holographic boundary of an asymptotic ADS$_5$ bulk. The tachyon field that drives inflation is represented by a DBI action on the brane. We solve the evolution equations analytically in the slow-roll regime and solve the exact equations numerically. We calculate the inflation parameters and compare the results with Planck 2018 data.

gr-qc↗

arXiv2018

Holographic cosmology and tachyon inflation

After a brief introduction to the AdS/CFT holography a tachyon inflation will be discussed in the framework of holographic cosmology. The model is based on a holographic braneworld scenario with an effective tachyon field on a D3-brane located at the holographic bound of an asymptotic ADS$_5$ bulk.

gr-qc↗

arXiv2017

Particle creation and reheating in a braneworld inflationary scenario

We study the cosmological particle creation in the tachyon inflation based on the D-brane dynamics in the RSII model extended to include matter in the bulk. The presence of matter modifies the warp factor which results in two effects: a modification of the RSII cosmology and a modification of the tachyon potential. Besides, a string theory D-brane supports among other fields a U(1) gauge field reflecting open strings attached to the brane. We demonstrate how the interaction of the tachyon with the U(1) gauge field drives cosmological creation of massless particles and estimate the resulting reheating at the end of inflation.

hep-th↗

arXiv2017

Tachyon inflation in an AdS braneworld with back-reaction

We analyze the inflationary scenario based on the tachyon field coupled with the radion of the second Randall-Sundrum model (RSII). The tachyon Lagrangian is derived from the dynamics of a 3-brane moving in the five dimensional bulk. The AdS$_5$ geometry of the bulk is extended to include the radion. Using the Hamiltonian formalism we find four nonlinear field equations supplemented by the modified Friedmann equations of the RSII braneworld cosmology. After a suitable rescaling we reduce the parameters of our model to only one free parameter related to the brane tension and the AdS$_5$ curvature. We solve the equations numerically assuming a reasonably wide range of initial conditions determined by physical considerations. Varying the free parameter and initial conditions we confront our results with the Planck 2015 data.

gr-qc↗

arXiv2016

Randall-Sundrum vs. Holographic Braneworld

A mapping between two braneworld cosmologies -- Randall-Sundrum and holographic -- is explicitly constructed. The cosmologies are governed by the appropriate modified Friedman equations. A relationship between the corresponding Hubble rates is established.

gr-qc↗

arXiv2016

Randall-Sundrum versus holographic cosmology

We consider a model of a holographic braneworld universe in which a cosmological fluid occupies a 3+1 dimensional brane located at the boundary of the asymptotic AdS$_5$ bulk. We combine the AdS/CFT correspondence and the second Randall-Sundrum (RSII) model to establish a relationship between the RSII braneworld cosmology and the boundary metric induced by the time dependent bulk geometry. In the framework of the Friedmann Robertson Walker cosmology we discuss some physically interesting scenarios involving the RSII and holographic braneworlds.

gr-qc↗

arXiv2015

Cosmological particle creation in a hadronic fluid

Acoustic perturbations in an expanding hadronic fluid at temperatures below the chiral transition point represent massless pions propagating in curved spacetime geometry. In comoving coordinates the corresponding analog metric tensor describes a hyperbolic FRW spacetime. We study the analog cosmological particle creation of pions below the critical point of the chiral phase transition. We compare the cosmological creation spectrum with the spectrum of analog Hawking radiation at the analog trapping horizon.

gr-qc↗

arXiv2013

AdS braneworld with Backreaction

We review the tachyon model derived from the dynamics of a 3-brane moving in the AdS5 bulk. The bulk geometry is based on the Randall-Sundrum II model extended to include the radion. The effective tachyon Lagrangian is modified due to the back-reaction of the brane on the bulk geometry.

hep-th↗

arXiv2013

FRW universe in the laboratory

We consider an expanding relativistic fluid with spherical symmetry as a model for an analog FRW spacetime. In the framework of relativistic acoustic geometry we demonstrate how to mimic an arbitrary FRW spacetime with positive, zero or negative spatial curvature. In the Lagrangian description we show that a particular FRW spacetime is obtained by choosing the appropriate potential. We discuss several examples and in particular the analog de Sitter spacetime in the coordinate representation with positive and negative spatial curvature.

gr-qc↗

arXiv2013

"Warm" Tachyon Matter from Back-reaction on the Brane

We study a 3-brane moving in the five-dimensional bulk of the Randall-Sundrum II model. By including back-reaction of the brane on the bulk geometry we obtain a tachyon model with a linear barotropic equation of state.

hep-th↗

arXiv2013

Trapped surfaces in a hadronic fluid

Pion propagation in a hadronic fluid with a non-homogeneous relativistic flow is studied in terms of the linear sigma model. The wave equation turns out to be equivalent to the equation of motion for a massless scalar field propagating in a curved spacetime geometry. The metric tensor depends locally on the soft pion dispersion relation and the four-velocity of the fluid. For a relativistic flow in curved spacetime the apparent and trapping horizons may be defined in the same way as in general relativity. An expression for the analog surface gravity is derived.

gr-qc↗

arXiv2012

Analogue surface gravity near the QCD chiral phase transition

Using the formalism of relativistic acoustic geometry we study the expanding chiral fluid in the regime of broken chiral symmetry near the QCD chiral phase transition temperature T_c. The dynamics of pions below T_c is described by the equation of motion for a massless scalar field propagating in curved spacetime similar to an open FRW universe. The metric tensor depends locally on the soft pion dispersion relation and the four-velocity of the fluid. In the neighborhood of the critical point an analogue trapped region forms with the analogue trapped horizon as its boundary. We show that the associated surface gravity diverges near the critical point as 1/(T_c-T). Hence, if the horizon forms close to the critical temperature the analogue Hawking temperature may be comparable with or even larger than the background fluid temperature.

hep-th↗