Showing papers in "Modern Physics Letters A in 2010"
TL;DR: In this paper, the authors provide a physical interpretation for the field equations of gravity based on a thermodynamic perspective, and the virtual degrees of freedom associated with the horizons, as perceived by the local Rindler observer, play a crucial role in this approach.
Abstract: It is possible to provide a physical interpretation for the field equations of gravity based on a thermodynamical perspective. The virtual degrees of freedom associated with the horizons, as perceived by the local Rindler observer, play a crucial role in this approach. In this context, the relation S = E/2T between the entropy (S), active gravitational mass (E) and temperature (T) — obtained previously in gr-qc/0308070 [CQG, 21, 4485 (2004)] — can be reinterpreted as the law of equipartition E = (1/2) nkBT where $n=\Delta A/L_{\rm P}^2$ is the number (density) of microscopic horizon degrees of freedom in an area ΔA. Conversely, one can use the equipartition argument to provide a thermodynamic interpretation of gravity, even in the nonrelativistic limit. These results emphasize the intrinsic quantum nature of all gravitational phenomena and diminishes the distinction between thermal phenomena associated with local Rindler horizons and the usual thermodynamics of macroscopic bodies in non-inertial frames. J...
348 citations
TL;DR: In this paper, it was shown that this modification of the uncertainty principle can be derived straightforwardly from the geometric properties of (anti-de Sitter) spacetime, and the connection between the so-called extended generalized uncertainty principle and triply special relativity was discussed.
Abstract: It has been proposed that on (anti)-de Sitter background, the Heisenberg uncertainty principle should be modified by the introduction of a term proportional to the cosmological constant. We show that this modification of the uncertainty principle can be derived straightforwardly from the geometric properties of (anti)-de Sitter spacetime. We also discuss the connection between the so-called extended generalized uncertainty principle and triply special relativity.
91 citations
TL;DR: The complete supersymmetric action for eleven-dimensional supergravity is presented in this article, which is polynomial in the scalar fermionic pure spinor superfield.
Abstract: The complete supersymmetric action for eleven-dimensional supergravity is presented. The action is polynomial in the scalar fermionic pure spinor superfield, and contains only a minor modification to the recently proposed three-point coupling.
76 citations
TL;DR: In this article, a nonlinear electrodynamics Lagrangian was used to remove singularities in black hole singularities by using the Oppenheimer-Volkoff equation.
Abstract: We propose a way to remove black hole singularities by using a particular nonlinear electrodynamics Lagrangian that has been recently used in various astrophysics and cosmological frameworks. In particular, we adapt the cosmological analysis discussed in a previous work to the black hole physics. Such analysis will be improved by applying the Oppenheimer–Volkoff equation to the black hole case. At the end, fixed the radius of the star, the final density depends only on the introduced quintessential density term � and on the mass.
73 citations
TL;DR: In this paper, the authors explore static plane symmetric vacuum solutions using the metric approach of the f(R) theory, and they have found a total of three plane-symmetric solutions with the well-known solutions in General Relativity.
Abstract: The modified theories of gravity, especially the f(R) theory, have attracted much attention in recent years. In this context, we explore static plane symmetric vacuum solutions using the metric approach of this theory. The field equations are solved using the assumption of constant scalar curvature which may be zero or nonzero. We have found a total of three plane symmetric solutions. The correspondence of these solutions with the well-known solutions in General Relativity is given.
69 citations
TL;DR: In this paper, the exact deflection angle α by an Ellis wormhole was derived in terms of proper radial distance l that covers the entire spacetime, and it was shown that the coordinate invariant language for two-way wormholes should be l rather than rS.
Abstract: A recent work by Dey and Sen derived the approximate light deflection angle α by an Ellis wormhole in terms of proper radial distance l that covers the entire spacetime. On the other hand, Bodenner and Will calculated the expressions for light bending in Schwarzschild geometry using various coordinates and showed that they all reduce to a single formula when re-expressed in the coordinate independent language of "circumferential radius" rC identified with the standard radial coordinate rS. We shall argue that the coordinate invariant language for two-way wormholes should be l rather than rS. Hence here we find the exact deflection α in Ellis wormhole geometry first in terms of l and then in terms of rS. We confirm the latter expression using three different methods. We argue that the practical measurement scheme does not necessarily single out either l or rS. Some errors in the literature are corrected.
66 citations
TL;DR: In this paper, the stationary Klein-Gordon equation is considered for the Coulomb potential in non-commutative space and the energy shift due to noncommutativity is obtained via the perturbation theory.
Abstract: In this paper the stationary Klein–Gordon equation is considered for the Coulomb potential in noncommutative space. The energy shift due to noncommutativity is obtained via the perturbation theory. Furthermore, we show that the degeneracy of the initial spectral line is broken in transition from commutative space to noncommutative space.
66 citations
TL;DR: In this article, it is shown that using a dark spinor field it is possible to have an equation of state that crosses the phantom divide, becoming a dark phantom spinor which evolves into dark energy.
Abstract: Ever since the first observations that we are living in an accelerating universe, it has been asked what dark energy is. There are various explanations, all of which have various drawbacks or inconsistencies. Here we show that using a dark spinor field it is possible to have an equation of state that crosses the phantom divide, becoming a dark phantom spinor which evolves into dark energy. This type of equation of state has been mildly favored by experimental data, however, in the past there were hardly any theories that satisfied this crossing without creating ghosts or causing a singularity which results in the universe essentially ripping. The dark spinor model converges to dark energy in a reasonable time frame avoiding the big rip and without attaining negative kinetic energy as it crosses the phantom divide.
61 citations
TL;DR: In this paper, the authors generalize the BRST transformations in Abelian rank-2 tensor field theory by allowing the parameter to be finite and field-dependent and show that such transformations play crucial role in studying the Abelian 2-form gauge theory in noncovariant gauges.
Abstract: We generalize the BRST transformations in Abelian rank-2 tensor field theory by allowing the parameter to be finite and field-dependent and show that such transformations play crucial role in studying the Abelian 2-form gauge theory in noncovariant gauges. The generating functionals in different effective theories are connected through these generalized BRST transformations with different choice of finite parameter. We further consider the generalization of the anti-BRST transformations and show that even anti-BRST transformations with the finite field dependent parameter relate the generating functional for different effective theories. Such generalized BRST/anti-BRST transformations are useful in connecting generating functionals corresponding to different effective theories. Field/antifield formulation of this Abelian 2-form gauge theory is also studied in the context of generalized BRST transformations. We show that generalized BRST transformation connects the generating functional corresponding to the different solutions of quantum master equation in field/antifield formulation.
56 citations
TL;DR: In this article, the minimal geometric deformation approach, which has been successfully used to generate exact interior solutions to Einstein's field equations for static braneworld stars with local and nonlocal bulk terms, is used to obtain the branworld version of the Schwarzschild's interior solution.
Abstract: In the context of the Randall–Sundrum braneworld, the minimal geometric deformation approach, which has been successfully used to generate exact interior solutions to Einstein's field equations for static braneworld stars with local and nonlocal bulk terms, is used to obtain the braneworld version of the Schwarzschild's interior solution. Using this new solution, the behavior of the Weyl functions is elucidated in terms of the compactness for different stellar distributions.
55 citations
TL;DR: In this article, the authors classified the effects of Lorentz violation on astrophysical photons into three categories: (i) time lags between photons with different energies; (ii) a cutoff of photon flux above the threshold energy of photon decay, γ→e++e-; (iii) new patterns in the spectra of multi-TeV photons and EeV photons, due to the absorption of background lights.
Abstract: Lorentz violation (LV) is predicted by some quantum gravity (QG) candidates, wherein the canonical energy–momentum dispersion relation, E2 = p2+m2, is modified. Consequently, new phenomena beyond the standard model are predicted. In particular, the presence of LV highly affects the propagation of astrophysical photons with very high energies from distant galaxies. In this paper, we review the updating theoretical and experimental results on this topic. We classify the effects into three categories: (i) time lags between photons with different energies; (ii) a cutoff of photon flux above the threshold energy of photon decay, γ→e++e-; (iii) new patterns in the spectra of multi-TeV photons and EeV photons, due to the absorption of background lights. As we can see, the details of LV effects on astrophysical photons depend heavily on the "phase space" of LV parameters. From observational aspects, available and upcoming instruments can study these phenomena hopefully, and shed light onto LV issues and QG theories. The most recent progresses and constraints on the ultra-high energy cosmic rays (UHECRs) are also discussed.
TL;DR: In this article, the authors consider conformally invariant form of the actions in Einstein, Weyl, Einstein-Cartan and Weyl space in general dimensions (> 2) and investigate the relations among them.
Abstract: We consider conformally invariant form of the actions in Einstein, Weyl, Einstein–Cartan and Einstein–Cartan–Weyl space in general dimensions (> 2) and investigate the relations among them. In Weyl space, the observational consistency condition for the vector field determining non-metricity of the connection can be obtained from the equation of motion. In Einstein–Cartan space a similar role is played by the vector part of the torsion tensor. We consider the case where the trace part of the torsion is the Kalb–Ramond type of field. In this case, we express conformally invariant action in terms of two scalar fields of conformal weight -1, which can be cast into some interesting form. We discuss some applications of the result.
[...]
TL;DR: In this paper, it was shown that causality is always preserved for ELKOs, which is a special case of causality in the cosmology of the ELKO.
Abstract: The importance for cosmology of the recently introduced ELKOs requires our deepest understanding of them and of all of their fundamental properties. Among these fundamental properties, a special one is causality: in the present paper, we show that causality is always preserved for ELKOs.
TL;DR: Using properly defined Feynman propagator, a nonzero imaginary contribution to the scalar field effective action in even-dimensional de Sitter space was obtained in this paper, and the obtained expression for the effective action showed particle production with the Gibbons-Hawking rate.
Abstract: Using properly defined Feynman propagator we obtain nonzero imaginary contribution to the scalar field effective action in even-dimensional de Sitter space. Such a propagator follows from the path integral in de Sitter space and obeys composition principle proposed in arXiv:0709.2899. The obtained expression for the effective action shows particle production with the Gibbons–Hawking rate.
TL;DR: In this article, the authors examined the evolution of the apparent horizon entropy extracted through relation between the gravitational equation and the first law of thermodynamics together with the matter field entropy inside the horizon.
Abstract: We investigate the validity of the generalized second law of thermodynamics on the (n - 1)-dimensional brane embedded in the (n + 1)-dimensional bulk. We examine the evolution of the apparent horizon entropy extracted through relation between gravitational equation and the first law of thermodynamics together with the matter field entropy inside the apparent horizon. We find that the apparent horizon entropy extracted through connection between gravity and the first law of thermodynamics satisfies the generalized second law of thermodynamics. This result holds regardless of whether there is the intrinsic curvature term on the brane or a cosmological constant in the bulk. The observed satisfaction of the generalized second law provides further support on the thermodynamical interpretation of gravity based on the profound connection between gravity and thermodynamics.
TL;DR: In this paper, Lie-algebraic deformations of Minkowski space with undeformed Poincare algebra are presented, and these deformations interpolate between Snyder and κ-Minkowski spaces.
Abstract: We present Lie-algebraic deformations of Minkowski space with undeformed Poincare algebra. These deformations interpolate between Snyder and κ-Minkowski space. We find realizations of noncommutative coordinates in terms of commutative coordinates and derivatives. Deformed Leibniz rule, the coproduct structure and star product are found. Special cases, particularly Snyder and κ-Minkowski in Maggiore-type realizations are discussed. Our construction leads to a new class of deformed special relativity theories.
TL;DR: In this article, the inflaton scalar potential is used to compute the (CMB) observables of inflation, associated with curvature perturbations (namely, the scalar and tensor spectral indices, and the tensor-to-scalar ratio).
Abstract: We revisit the old (fourth-order or quadratically generated) gravity model of Starobinsky in four space-time dimensions, and derive the (inflaton) scalar potential in the equivalent scalar-tensor gravity model. The inflaton scalar potential is used to compute the (CMB) observables of inflation, associated with curvature perturbations (namely, the scalar and tensor spectral indices, and the tensor-to-scalar ratio), including the new next-to-leading-order terms with respect to the inverse number of e-foldings. The results are compared to the recent (WMAP5) experimental bounds. We confirm both mathematical and physical equivalence between f(R) gravity theories and the corresponding scalar-tensor gravity theories.
TL;DR: In this paper, the authors considered the general problem of causal propagation for spinor fields and focus attention in particular on the case constituted by ELKO fields and showed that the problem is always solvable.
Abstract: We shall consider the general problem of causal propagation for spinor fields, focus attention in particular on the case constituted by ELKO fields and will show that the problem of causal propagation for ELKO fields is always solvable.
TL;DR: In this article, the effects of dark energy on dynamics of the collapsing fluid within the framework of metric f(R) gravity were studied. But the authors did not consider the effect of the energy on the fluid dynamics in general spherical symmetric spacetime.
Abstract: The purpose of this paper is to study the effects of dark energy on dynamics of the collapsing fluid within the framework of metric f(R) gravity. The fluid distribution is assumed to be locally anisotropic and undergoing dissipation in the form of heat flow, null radiations and shear viscosity. For this purpose, we take general spherical symmetric spacetime. Dynamical equations are obtained and also some special solutions are found by considering shearing expansion-free evolution of the fluid. It is found that dark energy affects the mass of the collapsing matter and rate of collapse but does not affect the hydrostatic equilibrium.
TL;DR: In this article, the authors derived the deformed Hamiltonian, expressed in terms of the commutative phase space variables, describing the particle moving in a central potential in the κ-spacetime.
Abstract: We study the modification of Newton's second law, upto first order in the deformation parameter a, in the κ-spacetime. We derive the deformed Hamiltonian, expressed in terms of the commutative phase space variables, describing the particle moving in a central potential in the κ-spacetime. Using this, we find the modified equations of motion and show that there is an additional force along the radial direction. Using Pioneer anomaly data, we set a bound for a. We also analyze the violation of equivalence principle predicted by the modified Newton's equation, valid up to first order in a and use this also to set an upper bound on a.
TL;DR: In this paper, simple standing wave solutions in a 5D spacetime with a ghost-like scalar field are constructed, and the nodes of these standing waves are "islands" of 4D anti-de Sitter spacetime.
Abstract: We construct simple standing wave solutions in a 5D spacetime with a ghost-like scalar field. The nodes of these standing waves are "islands" of 4D anti-de Sitter spacetime. In the case of increasing (decreasing) warp factor, there are a finite (infinite) number of nodes and thus a finite (infinite) number of anti-de Sitter island-universes having different gravitational and cosmological constants. This is similar to the landscape models, which postulate a large number of universes with different parameters.
TL;DR: In this article, it was shown that A4 alone alone can achieve neutrino tribimaximal mixing with only the help of lepton number with a specific renormalizable model.
Abstract: Neutrino tribimaximal mixing is obtained from the breaking of A4 to Z3 in the charged-lepton sector and to Z2 in the neutrino sector. To enforce this conflicting pattern, extra particles and symmetries are usually invoked, often accompanied by nonrenormalizable interactions and even extra dimensions. It is shown here in a specific renormalizable model how A4 alone will accomplish this, with only the help of lepton number.
TL;DR: In this article, a complete classification of gravitational waves according to their frequencies is presented, and the determination of dark energy equation, and probing the inflationary physics using space gravitational wave detectors are discussed.
Abstract: In this paper we first present a complete classification of gravitational waves according to their frequencies: (i) Ultra high frequency band (above 1 THz); (ii) Very high frequency band (100 kHz–1 THz); (iii) High frequency band (10 Hz–100 kHz); (iv) Middle frequency band (0.1 Hz–10 Hz); (v) Low frequency band (100 nHz–0.1 Hz); (vi) Very low frequency band (300 pHz–100 nHz); (vii) Ultra low frequency band (10 fHz–300 pHz); (viii) Hubble (extremely low) frequency band (1 aHz–10 fHz); (ix) Infra-Hubble frequency band (below 1 aHz). After briefly discussing the method of detection for different frequency bands, we review the concept and status of space gravitational-wave missions — LISA, ASTROD, ASTROD-GW, Super-ASTROD, DECIGO and Big Bang Observer. We then address to the determination of dark energy equation, and probing the inflationary physics using space gravitational wave detectors.
TL;DR: The stability of de Sitter spacetime in Horava-Lifshitz theory of gravity with projectability without detailed balance condition is studied in this article, where it is shown that the spin-0 graviton is stable for any given ξ, and free of ghost for ξ ≤ 0 in the infrared limit, where ξ is the dynamical coupling constant.
Abstract: The stability of de Sitter spacetime in Horava–Lifshitz theory of gravity with projectability but without detailed balance condition is studied. It is found that, in contrast to the case of the Minkowski background, the spin-0 graviton is now stable for any given ξ, and free of ghost for ξ ≤ 0 in the infrared limit, where ξ is the dynamical coupling constant.
TL;DR: Quintom models, with its Equation of State being able to cross the cosmological constant boundary w = -1, turns out to be attractive for phenomenological study as discussed by the authors.
Abstract: Quintom models, with its Equation of State being able to cross the cosmological constant boundary w = -1, turns out to be attractive for phenomenological study. It can not only be applicable for dark energy model for current universe, but also lead to a bounce scenario in the early universe.
TL;DR: In this paper, the explicit form of linearized gauge invariant interactions of scalar and general higher even spin fields in the AdSD space is obtained, and a generalized Weyl transformation is proposed and the corresponding Weyl invariant action is constructed.
Abstract: The explicit form of linearized gauge invariant interactions of scalar and general higher even spin fields in the AdSD space is obtained. In the case of general spin-l a generalized "Weyl" transformation is proposed and the corresponding "Weyl" invariant action is constructed. In both cases the invariant actions of the interacting higher even spin gauge field and the scalar field include the whole tower of invariant actions for couplings of the same scalar with all gauge fields of smaller even spin. For the particular value of l = 4, all results are in exact agreement with Ref. 1.
TL;DR: In this article, a freely falling holographic screen for the Schwarzschild and Reissner-Nordstrom black holes is considered and the authors evaluate the entropic force a la Verlinde.
Abstract: We consider a freely falling holographic screen for the Schwarzschild and Reissner–Nordstrom black holes and evaluate the entropic force a la Verlinde. When the screen crosses the event horizon, the temperature of the screen agrees to the Hawking temperature and the entropic force gives rise to the surface gravity for both of the black holes.
TL;DR: In this article, the combination of the principles of quantum theory and general relativity allow for a dynamical energy-momentum space and a phenomenologically viable seesaw formula for the cosmological constant in this context.
Abstract: We argue that the combination of the principles of quantum theory and general relativity allow for a dynamical energy–momentum space. We discuss the freezing of vacuum energy in such a dynamical energy–momentum space and present a phenomenologically viable seesaw formula for the cosmological constant in this context.
TL;DR: In this article, the authors review some interrelated aspects of thick braneworlds constructed within the framework of 5D gravity coupled to a scalar field depending on the extra dimension, and show that when analyzing localization of 4D gravity in this smooth version of the Randall-Sundrum model, a kind of dichotomy emerges.
Abstract: We review some interrelated aspects of thick braneworlds constructed within the framework of 5D gravity coupled to a scalar field depending on the extra dimension. It turns out that when analyzing localization of 4D gravity in this smooth version of the Randall–Sundrum model, a kind of dichotomy emerges. In the first case the geometry is completely smooth and the spectrum of the transverse traceless modes of the metric fluctuations shows a single massless bound state, corresponding to the 4D graviton, and a tower of massive states described by a continuous spectrum of Kaluza–Klein excitations starting from zero mass, indicating the lack of a mass gap. In the second case, there are two bound states, a massless 4D graviton and a massive excitation, separated by a mass gap from a continuous spectrum of massive modes; nevertheless, the presence of a mass gap in the graviton spectrum of the theory is responsible for a naked singularity at the boundaries (or spatial infinity) of the Riemannian manifold. However, the imposition of unitary boundary conditions, which is equivalent to eliminating the continuous spectrum of gravitational massive modes, renders these singularities harmless from the physical point of view, providing the viability of the model.
TL;DR: In this paper, an electrodynamics consistent with anisotropic transformations of spacetime with an arbitrary dynamic exponent z was studied and the equations of motion and conserved quantities were explicitly obtained.
Abstract: We study an electrodynamics consistent with anisotropic transformations of spacetime with an arbitrary dynamic exponent z. The equations of motion and conserved quantities are explicitly obtained. We show that the propagator of this theory can be regarded as a quantum correction to the usual propagator. Moreover, we obtain that both the momentum and angular momentum are not modified, but their conservation laws do change. We also show that in this theory the speed of light and the electric charge are modified with z. The magnetic monopole in this electrodynamics and its duality transformations are also investigated. For that we found that there exists a dual electrodynamics, with higher derivatives in the electric field, invariant under the same anisotropic transformations.