119122332
Bulk spacetimes for cosmological braneworlds with a time-dependent extra dimension
We explore the possibilities of constructing bulk spacetimes in five dimensions for warped braneworld models with a spatially flat Friedmann-Robertson-Walker line element on the 3-brane and with a time-dependent extra dimension. Our first step in this direction involves looking at the status of energy conditions when such a bulk line element is assumed. We check these conditions by analyzing the relevant inequalities--for specific functional forms (chosen to satisfy certain desirable features) of the warp factor--the cosmological scale factor, and the extra-dimensional scale factor. Subsequently, we aim to obtain solutions with different types of bulk matter sources. We begin with a general analysis of the solution space of nonsingular Randall-Sundrum-type bulk models with an exponential warp factor and a chosen equation of state. Thereafter, we focus on three specific bulk sources--the ordinary scalar field, the Brans-Dicke scalar, and the dilaton. In each case, we are able to solve the field equations and obtain desirable solutions, for which we once again check the viability of the energy conditions. We also show how one can place branes in the bulk using the junction conditions. The issue of resolution of the bulk singularities which appear in our solutions, using standard methods, is also presentedmore » briefly. In summary, we are able to demonstrate that it is indeed possible to construct viable bulk spacetimes for warped cosmological braneworlds with a time-varying extra dimension and with bulk matter satisfying the energy conditions.« less
118456479
Geodesic congruences in warped spacetimes
In this article, we explore the kinematics of timelike geodesic congruences in warped five-dimensional bulk spacetimes, with and without thick or thin branes. Beginning with geodesic flows in the Randall-Sundrum anti-de Sitter geometry without and with branes, we find analytical expressions for the expansion scalar and comment on the effects of including thin branes on its evolution. Later, we move on to congruences in more general warped bulk geometries with a cosmological thick brane and a time-dependent extra dimensional scale. Using analytical expressions for the velocity field, we interpret the expansion, shear and rotation (ESR) along the flows, as functions of the extra dimensional coordinate. The evolution of a cross-sectional area orthogonal to the congruence, as seen from a local observer's point of view, is also shown graphically. Finally, the Raychaudhuri and geodesic equations in backgrounds with a thick brane are solved numerically in order to figure out the role of initial conditions (prescribed on the ESR) and spacetime curvature on the evolution of the ESR.
118364144
5D non-symmetric gravity and geodesic confinement
This work focuses on an unexplored aspect of non-symmetric geometry where only the off-diagonal metric components along the extra dimension, in a 5-dimensional spacetime, are non-symmetric. We show that the energy densities of the stationary non-symmetric models are similar to that of brane models thereby mimicking the thick-brane scenario. We find that the massive test particles are confined near the location of the brane for both growing and decaying warp factors. This feature is unique to the non-symmetric nature of our model. We have also studied the dynamical models where standard 4D FLRW brane is embedded. Our analysis shows that the non-symmetric terms deconfine energy density at the early universe while automatically confine at late times.
120041988
Linear higher derivative field theories, entanglement entropy and quantum phase transition
Quantum systems described by linear, higher order spatial derivatives of the field exhibit a new kind of phase transition as the coupling strength of the higher order terms varies. This essentially happens because a fundamental change in the ratio of ground state energy eigenvalues, between linear and non-linear regime, takes place which leads to excitation of higher modes. The new phase has inverse relation with area.
119220882
Particle creation in the presence of a warped extra dimension
Particle creation in spacetimes with a warped extra dimension is studied. In particular, we investigate the dynamics of a conformally coupled, massless scalar field in a five-dimensional warped geometry where the induced metric on the 3-branes is that of a spatially flat cosmological model. We look at situations where the scale of the extra dimension is assumed (i) to be time independent or (ii) to have specific functional forms for time dependence. The warp factor is chosen to be that of the Randall–Sundrum model. With particular choices for the functional form of the scale factor (and also the function characterizing the time evolution of the extra dimension) we obtain the |βk|2, the particle number and energy densities after solving (wherever possible, analytically but, otherwise, numerically) the conformal scalar field equations. The behaviours of these quantities for the massless and massive Kaluza–Klein modes are examined. Our results show the effect of a warped extra dimension on particle creation and illustrate how the nature of particle production on the brane depends on the nature of warping, and the type of cosmological evolution as well as the temporal evolution of the extra dimension.
119285859
Entanglement signatures of phase transition in higher-derivative quantum field theories
We show that the variations of the ground state entanglement in linear, higher spatial derivative field theories at zero temperature have signatures of phase transition. Around the critical point, when the dispersion relation changes from linear to nonlinear, there is a fundamental change in the reduced density matrix leading to a change in the scaling of entanglement entropy. We suggest possible explanations involving both kinematical and dynamical effects. We discuss the implication of our work for 2D condensed matter systems, black-hole entropy, and models of quantum gravity.
117770423
Shear viscosity due to Landau damping from the quark-pion interaction
We have calculated the shear viscosity coefficient $\ensuremath{\eta}$ of the strongly interacting matter in the relaxation time approximation, where a quasiparticle description of quarks with their dynamical masses is considered from the Nambu-Jona-Lasinio model. Due to the thermodynamic scattering of quarks with pseudoscalar-type condensate (i.e., pion), a nonzero Landau damping will be acquired by the propagating quarks. This Landau damping may be obtained from the Landau cut contribution of the in-medium self-energy of a quark-pion loop, which is evaluated in the framework of real-time thermal field theory.
118447643
Generating intrinsic dipole anisotropy in the large scale structures
There have been recent reports of unexpectedly large velocity dipole in the NRAO VLA Sky Survey data. We investigate whether the excess in the NVSS dipole reported can be of cosmological origin. We assume a long wavelength inhomogeneous scalar perturbation of the form \alpha sin (\kappa z) and study its effects on the matter density contrasts. Assuming an ideal fluid model we calculate, in the linear regime, the contribution of the inhomogeneous mode to the density contrast. We calculate the expected dipole in the LSS for two cases, first assuming that the mode is still superhorizon everywhere, and second assuming the mode is subhorizon, but has crossed the horizon deep in matter domination and is subhorizon everywhere in the region of the survey (NVSS). In both cases we find that such an inhomogeneous scalar perturbation is sufficient to generate the reported values of dipole anisotropy in LSS. For the superhorizon modes we find values which are consistent with both CMB and NVSS results. We also predict signatures for the model which can be tested by future observations.