Quantum-theoretical description of the cosmological constant as the zero-point energy
The present paper seeks to construct a quantum theory of the cosmological constant in which its presently observed very small value emerges naturally.
gr-qc↗
SEARCH · Search arXiv
Results for “gr-qc”
Search indexed arXiv papers on artificial intelligence, large language models, computer vision and robotics. Read source abstracts and follow links to arXiv.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Higgs Particle Mass in Cosmology
A version of the Standard Model is considered, where the electroweak symmetry breaking is provided by cosmological initial data given for the zeroth Fourier harmonic of the Higgs field $<ϕ>$. The initial data symmetry breaking mechanism removes the Higgs field contribution to the vacuum energy density, possible creation of monopoles, and tachion behavior at high energies, if one imposes an ``inertial'' condition on the Higgs potential $\textsf{V}_{\rm Higgs}(<ϕ>)=0$. The requirement of zero radiative corrections to this {\em inertial} condition coincides with the limiting point of the vacuum stability in the Standard Model. The latter together with the direct experimental limit gives the prediction for the mass of the Higgs boson to be in the range $114 < m_h \lsim 134$ GeV.
hep-ph↗
Quantum gravity phenomenology via Lorentz violations
The search for a quantum theory of gravity has been one of the main aims of theoretical physics for many years by now. However the efforts in this direction have been often hampered by the lack of experimental/observational tests able to select among, or at least constrain, the numerous quantum gravity models proposed so far. This situation has changed in the last decade thanks to the realization that some QG inspired violations of Lorentz symmetry could be constrained using current experiments and observations. This study it is not only allowing us to test at higher and higher energies a fundamental symmetry of spacetime but it is also providing us with hints and perspectives about the fundamental nature of gravity.
gr-qc↗
On initial conditions for inflationary and bouncing cosmologies
We consider the question of deriving initial conditions for scalar fields in driving both an early and late quintessence phase. The dark energy field presents an unresolved uniformity problem. Further difficulties with initial conditions for assisted, kinetic and phantom inflation are presented. We review the use of the canonical measure and find the negative conclusions of Gibbons and Hawking can be allayed by means of a reasonable quantum cosmological input. We remark upon some attempts at incorporating inflationary schemes into cyclic and bouncing models.
gr-qc↗
The Kerr spacetime: A brief introduction
This chapter provides a brief introduction to the Kerr spacetime and rotating black holes, touching on the most common coordinate representations of the spacetime metric and the key features of the geometry -- the presence of horizons and ergospheres. The coverage is by no means complete, and serves chiefly to orient oneself when reading subsequent chapters.
gr-qc↗
Discovering the Kerr and Kerr-Schild metrics
An historical account of the reasoning that led to the discovery of the Kerr and Kerr-Schild metrics in 1963-1964, and their physical interpretation as rotating black holes, is presented.
gr-qc↗
Agujeros de Gusano en Gravedad (2+1)
Traversable wormholes are objects that present a lot of interest in the last years because of their geometric features and their relation with exotic matter. In this paper we presnt a review of the principal characteristics of traversable Morris-Thorne wormholes, their construction proccess and some aspects about the exotic matter that is needed in order to mantain them. Then, we use a junction proccess to obatin two specific wormhole solutions in the (2+1) gravity formalism with negative cosmological constant. The obtained solutions represent wormholes with an external spacetime correspondient to the BTZ black hole solution. We also show that exotic matter is needed to mantain these wormholes. ----- Los agujeros de gusano atravesables son objetos que presentan un gran interes en la actualidad debido a sus caracteristicas geometricas y a su relacion con la materia exotica. En el presente trabajo se muestra una revision de las caracteristicas de los agujeros de gusano atravesables al estilo de Morris y Thorne, al igual que el proceso de construccion y aspectos de la materia exotica necesaria para mantenerlos. Luego, se utiliza un proceso de juntura para construir dos soluciones especificas tipo agujero de gusano en el formalismo de la gravedad (2+1) con constante cosmologica negativa. Con esta construccion, se obtienen agujeros atravesables que se encuentran unidos a un espacio-tiempo externo correspondiente al agujero negro BTZ sin momento angular y sin carga electrica. Ademas de esto, se muestra que para mantener este tipo de solucion es necesaria la existencia de materia exotica, es decir, materia que viole las condiciones de energia.
gr-qc↗
Superluminal motion and closed signal curves
We discuss some properties of Lorentz invariant theories which allow for superluminal motion. We show that, if signals are always sent forward in time, closed curves along which signals propagate can be formed. This leads to problems with causality and with the second law of thermodynamics. Only if one singles out one frame with respect to which all signals travel forward in time, the formation of 'closed signal curves' can be prevented. However, the price to pay is that in some reference frames perturbations propagate towards the past or towards the future, depending on the direction of emission.
astro-ph↗
Comment on "Elementary Kaluza-Klein towers revisited"
Recently the spectrum of KK modes in the framework of one flat extra-dimensional scenario was revisited in the paper Phys. Rev. D74 (2006) 124013, (hep-th/0607246) on the basis of self-adjoint extension of the quantum mechanical operator determining the KK masses. In this Letter we note that the range of allowed boundary conditions on the KK modes is overestimated in above mentioned paper and give all allowed possibilities.
hep-th↗
Spacetime Indeterminacy and Holographic Noise
A new kind of quantum indeterminacy of transverse position is shown to arise from quantum degrees of freedom of spacetime, based on the assumption that classical trajectories can be defined no better than the diffraction limit of Planck scale waves. Indeterminacy of the angular orientation of particle trajectories due to wave/particle duality at the Planck scale leads to indeterminacy of a nearly-flat spacetime metric, described as a small nonvanishing quantum commutation relation between transverse position operators at different events along a null trajectory. An independent derivation of the same effect is presented based on the requirement of unitarity in black hole evaporation. The indeterminacy is interpreted as a universal holographic quantum spacetime noise, with a frequency-independent spectrum of metric perturbation amplitude, h_H^2^{1/2} \simeq \sqrt{l_P}=2.3 \times 10^{-22} /\sqrt{Hz}, where l_P denotes the Planck length. The effect is estimated to be directly measurable using current interferometer technology similar to LIGO and LISA.
gr-qc↗
Model of embedded spaces: the field equations
A study of the Model of Embedded Spaces (MES) with a relativistic version of Finslerian geometry is continued. The field equations of the MES (Einstein and Maxwell types) are derived, and this formally completes geometrization of classical electrodynamics. The minimal action principle leads to geometrization of the field sources (the right-hand sides of the equations) and, as a consequence, to a field hypothesis of matter, a direct confirmation of W. Clifford's ideas.
gr-qc↗
Generalized gauge-invariance for gravitational waves
The aim of this paper is to show the gauge-invariance on the response of interferometers to gravitational waves (GWs). In this process, after a review of results on the Tranverse-Traceless (TT) gauge, where, in general, the theoretical computations on GWs are performed, which is due for completness, we analyse the gauge of the local observer, which represents the gauge of a laboratory environment on Earth. The gauge-invariance between the two gauges is shown in its full angular and frequency dependences. In previous works in the literature this gauge-invariance was shown only in the low frequencies approximation or in the simplest geometry of the interferometer in respect to the propagating GW (i.e. both of the arms of the interferometer are perpendicular to the propagating GW). As far as the computation of the response functions in the gauge of the local observer is concerned, a common misconception about interferometers is also clarifed.
gr-qc↗
Phase Transition of Trapped Nuclear Exciton of Long-lived Rhodium Mossbauer States
We report experimental observations of the long-lived rhodium Mossbauer emissions by the time- and energy-resolved spectroscopy. The extraordinary observations manifest the open-up of photonic band gap in analogy to the superconducting gap of remarkable symmetry breakings at transition point. These observations are of potential importance for detecting gravitational waves and development of the two-photon gamma laser. Firstly, phase transitions shown by spectral evolution of characteristic emissions reveal the different aggregate exciton orderings at room temperature. Six different phases are identified by spectra profiles emitted from the color centers. Secondly, the cascade branching of the multipolar nuclear transition is discovered being the spontaneous cascade down-conversion to generate entangled gammas. The macroscopic angular distribution of entangled gammas from the polycrystalline sample manifests a global photon-nucleus-photon bound state across the grain boundaries. Thirdly, the gamma-energy distributions depending on exciton phases reveal the photonic band gap typically on the order of several hundred eV.
quant-ph↗
Nonlinear gravitons from the initial value constraints of GR in Ashtekar variables
In this paper we provide a possible realization of Penrose's idea of nonlinear gravitons by constructing a solution to the initial value constraints in Ashtekar variables. The solution inputs are a spatial SU(2) connection and two free functions of position, and can be constructed as a formal operatorial expansion in powers of the cosmological constant about spacetimes of Petrov Type O. We first present the linear case, and then provide a simple nonlinear example to first order using a spatially homogeneous connection.
gr-qc↗
Entropy of Schwarzschild Black Holes on DGP Brane
We study the entropy of Schwarzschild black holes on DGP brane. The radius of event horizon on DGP brane is obtained by a numerical method. It is smaller than that of Einstein gravity in the conventional branch, and is larger in the accelerated branch. However, the difference is very small. The entropy of the black hole is calculated by using the improved brick-wall method.
gr-qc↗
Dark matter from "strong gravity" - consistent with CRESST, CoGeNT and DAMA/LIBRA
Kelso, Hooper and Buckley [arXiv:1110.5338] found CRESST, CoGeNT and DAMA/LIBRA results are consistent with 10 - 15 GeV dark matter particles. Hennawi and Ostriker [arXiv:astro-ph/0108203] analyzed supermassive black hole formation in the centers of galaxies, finding a best fit for dark matter (self-interaction cross-section)/mass ratio = 0.02 cm^{2}/g, with round-off error of 25%. Combining the Hennawi/Ostriker result with the "strong gravity" model for dark matter [arXiv:0706.3050] requires dark matter particles with mass between 10.5 GeV and 17.5 GeV, overlapping the Kelso/Hooper/Buckley dark matter particle mass range.
gr-qc↗
The Equations of Motion of a Charged Particle in the Five-Dimensional Model of the General Relativity Theory with the Four-Dimensional Nonholonomic Velocity Space
We consider the four-dimensional nonholonomic distribution defined by the 4-potential of the electromagnetic field on the manifold. This distribution has a metric tensor with the Lorentzian signature $(+,-,-,-)$, therefore, the causal structure appears as in the general relativity theory. By means of the Pontryagin's maximum principle we proved that the equations of the horizontal geodesics for this distribution are the same as the equations of motion of a charged particle in the general relativity theory. This is a Kaluza -- Klein problem of classical and quantum physics solved by methods of sub-Lorentzian geometry. We study the geodesics sphere which appears in a constant magnetic field and its singular points. Sufficiently long geodesics are not optimal solutions of the variational problem and define the nonholonomic wavefront. This wavefront is limited by a convex elliptic cone. We also study variational principle approach to the problem. The Euler -- Lagrange equations are the same as those obtained by the Pontryagin's maximum principle if the restriction of the metric tensor on the distribution is the same.
math.DG↗
Linear Stability of Closed Timelike Geodesics
The linear stability of closed timelike geodesics (CTGs) is analyzed in two spacetimes with cylindrical sources, an infinite rotating dust cylinder, and a cylindrical cloud of static cosmic strings with a central spinning string. We also study the existence and linear stability of closed timelike curves in spacetimes that share some common features with the Gödel universe (Gödel-type spacetimes). In this case the existence of CTGs depends on the `background' metric. The CTGs in a subclass of inhomogeneous stationary cosmological solutions of the Einstein-Maxwell equations with topology $ S^3\times \mathbb R$ are also examined.
gr-qc↗