Showing papers in "Modern Physics Letters A in 2008"
TL;DR: In this article, a method to find consistent solutions to Einstein's field equations in the interior of a spherically symmetric, static and non-uniform stellar distribution with Weyl stresses is developed.
Abstract: In the context of the braneworld, a method to find consistent solutions to Einstein's field equations in the interior of a spherically symmetric, static and non-uniform stellar distribution with Weyl stresses is developed. This method, based on the fact that any braneworld stellar solution must have the general relativity solution as a limit, produces a constraint which reduces the degrees of freedom on the brane. Hence the nonlocality and non-closure of the braneworld equations can be overcome. The constraint found is physically interpreted as a necessary condition to regain general relativity, and a particular solution for it is used to find an exact and physically acceptable analytical internal solution to no-uniform stellar distributions on the brane. It is shown that such an exact solution is possible due to the fact that bulk corrections to pressure, density and a metric component are a null source of anisotropic effects on the brane. A conjecture is proposed regarding the possibility of finding physically relevant exact solutions to non-uniform stellar distributions on the brane.
211 citations
TL;DR: In this paper, the authors give an introduction to the black hole solutions of Lovelock theory and analyze their most important properties, which can be regarded as generalizations of the Boulware-Deser solution of Einstein-Gauss-Bonnet gravity, which they discuss in detail here.
Abstract: Lovelock theory is a natural extension of Einstein theory of gravity to higher dimensions, and it is of great interest in theoretical physics as it describes a wide class of models. In particular, it describes string theory inspired ultraviolet corrections to Einstein–Hilbert action, while admits the Einstein general relativity and the so-called Chern–Simons theories of gravity as particular cases. Here, we give an introduction to the black hole solutions of Lovelock theory and analyze their most important properties. These solutions can be regarded as generalizations of the Boulware–Deser solution of Einstein–Gauss–Bonnet gravity, which we discuss in detail here. We briefly discuss some recent progress in understanding these and other solutions, like topological black holes that represent black branes of the theory, and vacuum thin-shell wormhole-like geometries that connect two different asymptotically de Sitter spaces. We also make some comments on solutions with time-like naked singularities.
194 citations
TL;DR: In this paper, it is shown that this coupling is generically too strong to be compatible with local tests of gravity and a possible way out, the chameleon effect, is also briefly investigated.
Abstract: Models where the accelerated expansion of our Universe is caused by a quintessence scalar field are reviewed In the framework of high energy physics, the physical nature of this field is discussed and its interaction with ordinary matter is studied and explicitly calculated It is shown that this coupling is generically too strong to be compatible with local tests of gravity A possible way out, the chameleon effect, is also briefly investigated
115 citations
TL;DR: In this article, the possibility of direct detection of a Light Dark Matter candidate is investigated considering the inelastic scattering processes on the electron or on the nucleus targets, and some theoretical arguments are developed and related phenomenological aspects are discussed.
Abstract: Some extensions of the Standard Model provide Dark Matter candidate particles with sub-GeV mass. These Light Dark Matter particles have been considered for example in Warm Dark Matter scenarios (e.g. the keV scale sterile neutrino, axino or gravitino). Moreover, MeV scale DM candidates have been proposed in supersymmetric models and as source of the 511 keV line from the Galactic center. In this paper the possibility of direct detection of a Light Dark Matter candidate is investigated considering the inelastic scattering processes on the electron or on the nucleus targets. Some theoretical arguments are developed and related phenomenological aspects are discussed. Allowed volumes and regions for the characteristic phenomenological parameters of the considered scenarios are derived from the DAMA/NaI annual modulation data.
95 citations
TL;DR: In this paper, a special class of scalar-tensor theories with charged black holes was considered, where the causal structure of the black holes has a single, non-degenerate horizon and their causal structure resembles that of the Schwarzschild black hole.
Abstract: Recent results show that when nonlinear electrodynamics is considered, the no-scalar-hair theorems in the scalar–tensor theories (STT) of gravity, which are valid for the cases of neutral black holes and charged black holes in the Maxwell electrodynamics, can be circumvented.1,2 What is even more, in the present work, we find new non-unique, numerical solutions describing charged black holes coupled to nonlinear electrodynamics in a special class of scalar–tensor theories. One of the phases has a trivial scalar field and coincides with the corresponding solution in General Relativity. The other phases that we find are characterized by the value of the scalar field charge. The causal structure and some aspects of the stability of the solutions have also been studied. For the scalar–tensor theories considered, the black holes have a single, non-degenerate horizon, i.e. their causal structure resembles that of the Schwarzschild black hole. The thermodynamic analysis of the stability of the solutions indicates that a phase transition may occur.
84 citations
TL;DR: In this article, the authors investigated the detection rates for Dark Matter candidates arise in a SU(2)L×U(1)Y with an additional doublet Higgs proposed by Barbieri, Hall and Rychkov.
Abstract: We investigate direct detection rates for Dark Matter candidates arise in a SU(2)L×U(1)Y with an additional doublet Higgs proposed by Barbieri, Hall and Rychkov. We refer to this model as "Heavy Higgs Model". The Standard Model Higgs mass comes out from this model is very heavy, so there is very slim chance that there is no Higgs boson mass below 200 GeV. The additional Higgs boson develops neither any VEV due to the choice of coefficient of the scalar potential of the model nor it has any coupling with fermions due to the incorporation of a discrete parity symmetry. Thus, the neutral components of the extra doublet are stable and can be considered as probable candidate of Cold Dark Matter. We have made calculations for three different types of Dark Matter experiments, namely, 76Ge (like GENIUS), DAMA (NaI) and XENON (131Xe). Also demonstrated the annual variation of Dark Matter detection in case of all three
83 citations
TL;DR: In this article, the authors investigated the gravitational lensing by two wormholes, viz., Janis-Newman-Winnicour (JNW) wormhole and Ellis wormhole.
Abstract: We have investigated the gravitational lensing by two wormholes, viz., Janis–Newman–Winnicour (JNW) wormhole and Ellis wormhole. The deflection angles in the strong field limit are calculated and various lens parameters of two wormholes are compared. It is shown that the JNW wormhole exhibits the relativistic images, while the Ellis wormhole does not have any relativistic image due to the absence of its photon sphere.
80 citations
TL;DR: In this article, a semi-analytic approach to the computation of the nonlinear power spectrum of dark matter density fluctuations is proposed, which can be applied down to zero redshift and to length scales where perturbation theory fails.
Abstract: Renormalization Group techniques, successfully employed in quantum field theory and statistical physics, are applied to study the dynamics of structure formation in the Universe. A semi-analytic approach to the computation of the nonlinear power-spectrum of dark matter density fluctuations is proposed. The method can be applied down to zero redshift and to length scales where perturbation theory fails. Our predictions accurately fit the results of numerical simulations in reproducing the "acoustic oscillations" features of the power spectrum, which will be accurately measured in future galaxy surveys and will provide a probe to distinguish among different dark energy models.
79 citations
TL;DR: In this article, the authors investigate the new agegraphic dark energy models with generalized uncertainty principle (GUP), and they find that although the GUP affects the early universe, it does not change the current and future dark energy-dominated universe significantly.
Abstract: We investigate the new agegraphic dark energy models with generalized uncertainty principle (GUP). It turns out that although the GUP affects the early universe, it does not change the current and future dark energy-dominated universe significantly. Furthermore, this model could describe the matter-dominated universe in the past only when the parameter n is chosen to be n > nc, where the critical value is determined to be nc = 2.799531478.
75 citations
TL;DR: In this article, the linear finite irreducible representations of the algebra of the 1D N-Extended Supersymmetric Quantum Mechanics are discussed in terms of their "connectivity" (a symbol encoding information on the graphs associated to the irreps).
Abstract: The linear finite irreducible representations of the algebra of the 1D N-Extended Supersymmetric Quantum Mechanics are discussed in terms of their "connectivity" (a symbol encoding information on the graphs associated to the irreps). The classification of the irreducible representations with the same fields content and different connectivity is presented up to N ≤ 8.
53 citations
TL;DR: In this article, the authors review what can (and cannot) be learned if dark matter is detected in one or more experiments, emphasizing the importance of combining LHC data with direct, astrophysical and cosmological probes of dark matter.
Abstract: We review what can (and cannot) be learned if dark matter is detected in one or more experiments, emphasizing the importance of combining LHC data with direct, astrophysical and cosmological probes of dark matter. We briefly review the conventional picture of a thermally produced WIMP relic density and its connection with theories of electroweak symmetry breaking. We then discuss both experimental and theoretical reasons why one might generically expect this picture to fail. If this is the case, we argue that a combined effort bringing together all types of data — combined with explicitly constructed theoretical models — will be the only way to achieve a complete understanding of the dark matter in our universe and become confident that any candidate actually provides the relic density.
TL;DR: In this article, a modified Majid-Ruegg bi-crossproduct basis was proposed for the quantization of field oscillators for the κ-deformed free scalar fields on the Minkowski space.
Abstract: We consider κ-deformed relativistic symmetries described algebraically by modified Majid–Ruegg bi-cross-product basis and investigate the quantization of field oscillators for the κ-deformed free scalar fields on κ-Minkowski space. By modification of standard multiplication rule, we postulate the κ-deformed algebra of bosonic creation and annihilation operators. Our algebra permits one to define the n-particle states with classical addition law for the four-momentum in a way which is not in contradiction with the nonsymmetric quantum four-momentum co-product. We introduce κ-deformed Fock space generated by our κ-deformed oscillators which satisfy the standard algebraic relations with modified κ-multiplication rule. We show that such a κ-deformed bosonic Fock space is endowed with the conventional bosonic symmetry properties. Finally we discuss the role of κ-deformed algebra of oscillators in field-theoretic noncommutative framework.
TL;DR: In this paper, the results of numerical analysis of parameter space are compared with WMAP3 data to find the appropriate new constraints on the values of the non-minimal coupling.
Abstract: The Wilkinson Microwave Anisotropy Probe (WMAP) three-year results are used to constraint non-minimal inflation models. Two different non-minimally coupled scalar field potentials are considered to calculate the corresponding slow-roll parameters of non-minimal inflation. The results of numerical analysis of parameter space are compared with WMAP3 data to find the appropriate new constraints on the values of the non-minimal coupling.
TL;DR: In this article, the Lie derivative of a second rank tensor is defined in the context of the teleparallel theory of gravity and also extended to general tensors of rank p + q. This definition is then used to find the Killing vectors of the Einstein universe.
Abstract: In this paper we establish the definition of the Lie derivative of a second rank tensor in the context of teleparallel theory of gravity and also extend it for a general tensor of rank p + q. This definition is then used to find Killing vectors of the Einstein universe. It turns out that Killing vectors of the Einstein universe in the teleparallel theory are the same as in general relativity.
TL;DR: In this article, the Ruppeiner metrics are modified to induce curvature in a rotating BTZ black hole model and some supporting calculations are carried out for the relatively simple model.
Abstract: There has been some recent controversy regarding the Ruppeiner metrics that are induced by Reissner–Nordstrom (and Reissner–Nordstrom-like) black holes. Most infamously, why does this family of metrics turn out to be flat, how is this outcome to be physically understood, and can/should the formalism be suitably modified to induce curvature? In this paper, we provide a novel interpretation of this debate. For the sake of maximal analytic clarity and tractability, some supporting calculations are carried out for the relatively simple model of a rotating BTZ black hole.
TL;DR: In this paper, it was shown that DAMA/NaI results could be caused by 6×10-7 cm-2 s-1 flux of daemons (Dark Electric Matter Objects) falling out from strongly elongated heliocentric orbits with velocities of 30-50 km/s.
Abstract: Energy of ions (recoil nuclei) channeled along definite directions in crystals is transferred to the lattice electrons mainly. In NaI(Tl)-type scintillators, this leads to increasing the light yield from ~ 10% to ~ 100% when compared with the yield for electrons of the same energy. Taking into account this effect at processing data of DAMA/NaI experiments in Gran Sasso, which had demonstrated the year modulation of number of signals in a range of 2–6 keV of electron equivalent, reveals that DAMA/NaI results could be caused by ~ 6×10-7 cm-2 s-1 flux of daemons (Dark Electric Matter Objects — presumably Planckian relic particles) falling out from strongly elongated heliocentric orbits with velocities of 30–50 km/s. The flux value and the 2–6 keV signal intensity agree rather well with values emerging from our former estimates and interpretations of ground-level and underground measurements.
TL;DR: In this paper, a polytropic equation-of-state p = ωρn is chosen for some of the kinematical Λ-models viz., $\Lambda \sim (\dot a/a)^2$,
Abstract: Equation-of-state parameter plays a significant role for guessing the real nature of dark energy. Here polytropic equation-of-state p = ωρn is chosen for some of the kinematical Λ-models viz., $\Lambda \sim (\dot a/a)^2$, $\Lambda \sim \ddot a/a$ and Λ ~ ρ. Although in dust cases (ω = 0) closed form solutions show no dependency on the polytropic index n, but in non-dust situations some new possibilities are opened up including phantom energy with supernegative (ω < -1) equation-of-state parameter.
TL;DR: In this paper, the state-finder diagrams of the tachyon dark energy model were analyzed and it was shown that the evolving trajectories of the attractor solutions lie in the total region and pass through the LCDM fixed point.
Abstract: In this paper we study the statefinder parameters for the tachyon dark energy model. There are two kinds of stable attractor solutions in this model. The statefinder diagrams characterize the properties of the tachyon dark energy model. Our results show that the evolving trajectories of the attractor solutions lie in the total region and pass through the LCDM fixed point, which is different from other dark energy model.
TL;DR: The status and plans of a research program on the development of ultra-low-energy germanium detectors with sub-keV sensitivities are reported in this paper, which includes neutrino-nucleus coherent scattering, the studies of neutrinos magnetic moments, as well as the searches of WIMP dark matter.
Abstract: The status and plans of a research program on the development of ultra-low-energy germanium detectors with sub-keV sensitivities are reported. We survey the scientific goals which include the observation of neutrino-nucleus coherent scattering, the studies of neutrino magnetic moments, as well as the searches of WIMP dark matter. In particular, a threshold of 100-200 eV and a sub-keV background comparable to underground experiments were achieved with prototype detectors. New limits were set for WIMPs with mass between 3–6 GeV. The prospects of the realization of full-scale experiments are discussed.
TL;DR: In this paper, it is shown how high energy neutrino beams from very distant sources can be utilized to learn about many properties of neutrinos such as lifetimes, mass hierarchy, mixing, minuscule pseudo-Dirac mass splittings and other exotic properties; in addition, the production mechanism of neut rinos in astrophysical sources can also be elucidated.
Abstract: It is shown how high energy neutrino beams from very distant sources can be utilized to learn about many properties of neutrinos such as lifetimes, mass hierarchy, mixing, minuscule pseudo-Dirac mass splittings and other exotic properties; in addition, the production mechanism of neutrinos in astrophysical sources can also be elucidated.
TL;DR: In this article, a functional approach was employed to investigate the confinement problem in quenched Landau gauge QCDs and showed that a linear rising potential between massive quarks is generated by infrared singularities in the dressed quark-gluon vertex.
Abstract: We employ a functional approach to investigate the confinement problem in quenched Landau gauge QCD. We demonstrate analytically that a linear rising potential between massive quarks is generated by infrared singularities in the dressed quark–gluon vertex. The self-consistent mechanism that generates these singularities is driven by the scalar Dirac amplitudes of the full vertex and the quark propagator. These can only be present when chiral symmetry is broken. We have thus uncovered a novel mechanism that directly links chiral symmetry breaking with confinement.
TL;DR: In this paper, the authors describe various nonrelativistic contractions of twisted Poincare algebra, including the canonical one (θμν-deformation) and the one leading to Lie-algebraic models of noncommutative spacetimes.
Abstract: We describe various nonrelativistic contractions of two classes of twisted Poincare algebra: canonical one (θμν-deformation) and the one leading to Lie-algebraic models of noncommutative spacetimes. The cases of contraction-independent and contraction-dependent twist parameters are considered. We obtain five models of noncommutative nonrelativistic spacetimes, in particular, two new Lie-algebraic nonrelativistic deformations of spacetime, respectively, with quantum time/classical space and with quantum space/classical time.
TL;DR: In this article, a regular solution of the system of coupled equations of the nonlinear electrodynamics and gravity describing static and spherically-symmetric black holes in an asymptotically de Sitter universe is constructed and analyzed.
Abstract: A regular solution of the system of coupled equations of the nonlinear electrodynamics and gravity describing static and spherically-symmetric black holes in an asymptotically de Sitter universe is constructed and analyzed. Special emphasis is put on the degenerate configurations (when at least two horizons coincide) and their near horizon geometry. It is explicitly demonstrated that approximating the metric potentials in the region between the horizons by simple functions and making use of a limiting procedure one obtains the solutions constructed from maximally symmetric subspaces with different absolute values of radii. Topologically they are AdS2×S2 for the cold black hole, dS2×S2 when the event and cosmological horizon coincide, and the Plebanski–Hacyan solution for the ultraextremal black hole. A physically interesting solution describing the lukewarm black holes is briefly analyzed.
TL;DR: In this paper, two simple parametrized deceleration parameters are constrained by using the latest SNe Ia Gold dataset, observational Hubble data, and their combination, and a tight constraint is obtained.
Abstract: In this paper, two simple parametrized deceleration parameters and areconstrained by using the latest SNe Ia Gold dataset, observational Hubble data and their combination. It is found that the transition redshift from decelerated expansion to accelerated expansion zT and current decelerated parameter values q0 are consistent with each other in 1σ region by only using SNe Ia Gold dataset and observational Hubble data in three parametrizations respectively. By combining the SNe Ia Gold dataset and observational Hubble data together, a tight constraint is obtained. With this combined constraint, zT is and with 1σ error in the parametrizations respectively.
TL;DR: In this paper, the authors study finite temperature phase transition of neutral scalar field on a fuzzy sphere using Monte Carlo simulations and show the presence of meta-stable states, first order symmetry breaking transition and existence of multiple triple points in the phase diagram.
Abstract: We study finite temperature phase transition of neutral scalar field on a fuzzy sphere using Monte Carlo simulations. We work with the zero mode in the temporal directions, while the effects of the higher modes are taken care by the temperature dependence of r. In the numerical calculations we use "pseudo-heatbath" method which reduces the auto-correlation considerably. Our results agree with the conventional calculations. We report some new results which show the presence of meta-stable states, first order symmetry breaking transition and existence of multiple triple points in the phase diagram..
TL;DR: In this paper, an improved form of the hyperfine interaction and isospin dependent quark potential was introduced to describe the baryon spectrum for energies lower than 1.7 GeV.
Abstract: The constituent quark model (CQM) has recently been widely used for the description of the internal structure of baryons. The baryon spectrum is usually well described, although various models are quite different. However, the study of baryon spectroscopy is not sufficient to distinguish among the various forms of quark dynamics. It would be interesting to consider the effect of an extra residual interaction among the quarks, which contains a dependence on isospin (or flavor). In the chiral constituent quark model the non-confining part of the potential is provided by the interaction with the Goldstone bosons, giving rise to a spin- and isospin-dependent part which is crucial for the description of the spectrum for energies lower than 1.7 GeV. In this work we have introduced an improved form of the hyperfine interaction and isospin dependent quark potential. The resulting description of the baryon spectrum was found to be satisfactory and we not only have included confinement potential at large separation...
TL;DR: In this paper, the authors proposed a mechanism to arise warped braneworld models from bulk tachyon matter, which are endowed with a thin brane and a thick brane.
Abstract: Recently, Pal and Skar in Ref. 33 proposed a mechanism to arise the warped braneworld models from bulk tachyon matter, which are endowed with a thin brane and a thick brane. In this framework, we investigate localization of fermionic fields on these branes. As in the 1/2-spin case, the field can be localized on both the thin and thick branes with inclusion of scalar background. In the 3/2-spin extension, the general supergravity action coupled to chiral supermultiplets is considered to produce the localization on both the branes as a result.
TL;DR: The hypothesis that dark matter consists of superheavy particles with the mass close to the Grand Unification scale is investigated in this paper, where numerical estimates of the effect leading to the observable numbers are given.
Abstract: The hypothesis that dark matter consists of superheavy particles with the mass close to the Grand Unification scale is investigated. These particles were created from vacuum by the gravitation of the expanding Universe and their decay led to the observable baryon charge. Some part of these particles with the lifetime larger than the time of breaking of the Grand Unification symmetry became metastable and survived up to the modern time as dark matter. However, in active galactic nuclei due to large energies of dark matter particles swallowed by the black hole and the possibility of the Penrose process for rotating black hole the opposite process can occur. Dark matter particles become interacting. Their decay on visible particles at the Grand Unification energies leads to the flow of ultra high energy cosmic rays observed by the Auger group. Numerical estimates of the effect leading to the observable numbers are given.
TL;DR: In this article, a Brans-Dicke brane cosmology with two scalar fields inspired from string theories and phenomenological effective cosmological constant is investigated and some features are described in some details, in particular the low and high energies limit.
Abstract: A Brans–Dicke brane cosmology with two scalar fields inspired from string theories and phenomenological effective cosmological constant is investigated and some features are described in some details, in particular the low and high energies limit.
TL;DR: In this article, the authors examined the content of the contracting universe and its entropy Scu and found that beyond dark energy, the universe contains on average zero or an unlikely single photon which if present immediately after turnaround would have infinitesimal energy that blue shifts eventually to produce e+e-pair.
Abstract: Following up a recent proposal1 for a cyclic model based on phantom dark energy, we examine the content of the contracting universe (cu) and its entropy Scu. We find that beyond dark energy, the universe contains on average zero or an unlikely single photon which if present immediately after turnaround would have infinitesimal energy that blue shifts eventually to produce e+e- pairs. These statements are independent of the equation of state ω = p/ρ of dark energy provided ω < -1. Thus Scu = 0 and if observations confirm ω < -1, the entropy problem is solved. We discuss the absence of a theoretical lower bound on ϕ = |ω+1|, then describe an anthropic fine tuning argument that renders unlikely extremely small ϕ. The present bound ϕ ≲ 0.1 already implies a time until turnaround of (tT - t0) ≳ 100 Gy.