118627890
Beyond the Einstein Equation of State: Wald Entropy and Thermodynamical Gravity
We show that the classical equations of gravity follow from a thermodynamic relation, dQ = T dS, where S is taken to be the Wald entropy, applied to a local Rindler horizon at any point in spacetime. Our approach works for all diffeomorphism-invariant theories of gravity. This suggests that classical gravity may be thermodynamic in origin.
120714502
The Membrane Paradigm for Gauss-Bonnet gravity
We construct the membrane paradigm for black objects in Einstein-Gauss-Bonnet gravity in spacetime dimensions $ \ge 5$. As in the case of general relativity, for the observers outside the horizon the dynamics of the perturbations of the horizon can be modelled as a membrane endowed with fluid-like properties. We derive the stress-tensor for this membrane fluid and study the perturbation around static backgrounds with constant curvature horizon cross-section to express the stress tensor in the form of a Newtonian viscous fluid with pressure, shear viscosity and bulk viscosity. The ratio of the shear viscosity and the entropy density is shown to generically violate the bound suggested by Policastro, Son and Starinets. We evaluate the transport coefficients for some static geometries. For the black brane geometry our results match with those available in the literature. For the spherically symmetric AdS black hole our results can be interpreted as a holographic prediction for the transport coefficients and viscosity to the entropy density ratio for the dual conformal field theory living on the boundary, $S^3 \times R$.
201072483
Corrections to the Bekenstein-Hawking entropy in the brick wall approach
The brick wall model is a semi-classical approach to underst and he microscopic origin of black hole entropy. In this approach, the entropy of the black hole arises due to the canonical entropy of matter fields outside the black hole event horizon, evaluate d the Hawking temperature. Usually, in the brick wall model, the density of states and the resulti ng canonical entropy of the matter fields are calculated at the leading order (in terms of h̄) in the WKB approximation. We extend this approach and compute the brick wall entropy of a quantum scalar field around static and spherically symmetric black holes at the higher orders in th e WKB approximation. We find that the brick wall model generally predicts corrections to the B kenstein-Hawking entropy in all spacetime dimensions. We compare our results with the sub-l eading contributions to the black hole entropy that has been obtained from various other appro ches.
44195025
Subleading contributions to the black hole entropy in the brick wall approach
The brick wall model is a semiclassical approach to understand the microscopic origin of black hole entropy. In this approach, the black hole geometry is assumed to be a fixed classical background on which matter fields propagate, and the entropy of black holes supposedly arises due to the canonical entropy of matter fields outside the black hole event horizon, evaluated at the Hawking temperature. Apart from certain lower dimensional cases, the density of states of the matter fields around black holes cannot be evaluated exactly. As a result, often, in the brick wall model, the density of states and the resulting canonical entropy of the matter fields are evaluated at the leading order (in terms of ({Dirac_h}/2{pi})) in the WKB approximation. The success of the approach is reflected by the fact that the Bekenstein-Hawking area law - viz. that the entropy of black holes is equal to one-quarter the area of their event horizon, say, A{sub H} - has been recovered using this model in a variety of black hole spacetimes. In this work, we compute the canonical entropy of a quantum scalar field around static and spherically symmetric black holes through the brick wall approach at the higher ordersmore » (in fact, up to the sixth order in ({Dirac_h}/2{pi})) in the WKB approximation. We explicitly show that the brick wall model generally predicts corrections to the Bekenstein-Hawking entropy in all spacetime dimensions. In four dimensions, we find that the corrections to the Bekenstein-Hawking entropy are of the form [A{sub H}{sup n}logA{sub H}], while, in six dimensions, the corrections behave as [A{sub H}{sup m}+A{sub H}{sup n}logA{sub H}], where (m,n)<1. We compare our results with the corrections to the Bekenstein-Hawking entropy that have been obtained through the other approaches in the literature, and discuss the implications.« less
199678166
Horizon entropy and higher curvature equations of state
The Clausius relation between entropy change and heat flux has previously been used to derive Einstein's field equations as an equation of state. We examine here whether a similar derivation can be given for extensions beyond Einstein gravity to include higher derivative and higher curvature terms.
118315517
Thermodynamic Route to Field Equations in Gravity
Spacetimes with horizons show a resemblance to thermodynamic systems and one can associate notions of temperature and entropy with them. Such notions provide us a possible alternative approach to understand the dynamics of gravity as an emergent phenomenon resulted out of thermodynamics of spacetime by interpreting the field equations as a thermodynamic identity TdS = dE+PdV. Interestingly, such equilibrium thermodynamic interpretation works only for Lanczos‐Lovelock theories. All these prelimany results point towards a deep connection among gravity, thermodynamics and quantum theory and also offer a new outlook regarding the nature of gravitational interaction.
53492385
Mechanical prototype of tracking chamber in station 2 in dimuon spectrometer of ALICE
To explore the physics of ultra-relativistic heavy-ion collision, a large ion collider experiment (ALICE) [1] is proposed to carry out at large hadron collider (LHC). Forward muon spectrometer (FMS) [2] is included in ALICE to look for the signals of quark gluon plasma (QGP) using dileptonic decay of heavy quarkonia (J=ψ , γ) produced in the collision as a probe. The production of these states will be suppressed in a deconfined medium of QGP which can be estimated from the invariant mass spectrum of dimuonic decay channel. The spectrometer is designed to track down the flight path of the dimuons with the help of five tracking stations from which the opening angle of the pair can be known by reconstruction and extrapolation of their tracks. The momenta of the pairs can be obtained from the deviation of the tracks in a dipole magnetic field. The invariant mass of the pair can be determined from the opening angle and momenta of dimuon pairs. Each of the five tracking stations is equipped with two planes of cathode pad chamber each divided into four quadrants to detect the position of the dimuon passing through them and reconstruct their tracks from their positions. The tracking chambers are designed following the basic feature of a position sensitive multi-wire proportional counter (MWPC) where an anode wire plane is interposed between two cathode planes and a high electric field is maintained near the anode with respect to the cathodes. The chambers are capable of providing X, Y position readout of an event from the charge distribution induced over the cathode planes equipped with pad matrices due to the avalanche produced in the gaseous medium. However, the mechanical design of the large chamber (diameter 2 m) for the second tracking station is a challenging task as it concerns good surface planarity to achieve position resolution better than 100 μm (necessary to meet mass resolution about 100 MeV) as well as minimum usage of material to keep radiation length low (2–3% of X0) in order to minimise the energy loss and scattering of the incident lepton. The calculation was carried out at IPN, Orsay to simulate a full scale quadrant with different design parameters and materials to study its mechanical characteristics [3,4]. In the simulation, various options in material and design aspects were studied to seek an optimum design for the chamber to enhance its mechanical
120632246
Interacting holographic dark energy, cosmic coincidence and the future singularity of the closed FRW universe
Abstract In this paper, we have considered the closed FRW universe filled with two interacting fluids; dark matter and holographic dark energy components. Under certain conditions, this dark energy model is characterised by a big rip type future singularity and therefore a finite life time of the universe (Cruz et al., 2008). As the universe passes through a significant time when the matter and the dark energy densities are roughly comparable between the matter and the dark energy dominated era. So, we calculated the fraction of total life time of the universe when the universe passes through the coincidental stage for this future singularity by considering 1 r o r = ρ M ρ DE r o , where r 0 is any fixed ratio. It has been found that the time for the future singularity t s is very large when the value of the constant c is much closed to zero and the fraction is smaller for smaller values of r 0 . Comparison of the results with the observational data and its importance has also been discussed.
120382926
Some consequences of approximate recursion relations in lattice gauge theories
123143461
Interacting holographic dark energy with variable deceleration parameter and tachyon scalar field dark energy model in LRS Bianchi type-II universe
In this work, we have considered the spatially homogeneous and anisotropic Bianchi type-II universe filled with two interacting fluids; dark matter and holographic dark energy components. Assuming the proportionality relation between one of the components of shear scalar and expansion scalar which yields time dependent deceleration parameter, an exact solution to Einstein’s field equations in Bianchi type-II line element is obtained. We have investigated geometric and kinematics properties of the model and the behaviour of the holographic dark energy. It is observed that the mean anisotropic parameter is uniform through the whole evolution of the universe and the coincidence parameter increases with increasing time. The solutions are also found to be in good agreement with the results of recent observations. We have applied the statefinder diagnostics method to study the behaviour of different stages of the universe and to differentiate the proposed dark energy model from the ΛCDM model. We have also established a correspondence between the holographic dark energy model and the tachyon scalar field dark energy model. We have reconstructed the potential and the dynamics of the tachyon scalar field, which describes accelerated expansion of the universe.
15573377
A Note on matrix model with IR cutoff and AdS/CFT
We study effective gauge theory at finite temperature on a three-sphere in the presence of an IR cutoff using AdS/CFT. Comparing with the thermodynamic behavior of its gravity dual, we analyze a phenomenological matrix model which describes the gauge theory in the strongly coupled regime. Subsequently, we study the behavior of the model as a function of the IR cutoff. We further argue that a similar matrix model represents the effective gauge theory on R3 with an IR-cutoff and analyze the model numerically.