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F. R. Klinkhamer

Publications and source records attributed to F. R. Klinkhamer.

At least 91 records · Page 5Linked to original sources
arXiv2012

Superluminal neutrino, flavor, and relativity

Modified neutrino dispersion relations, which still obey the relativity principle, can have both a superluminal (muon-type) neutrino and a luminal (electron-type) neutrino, as long as neutrino-mass effects can be neglected. The idea is to allow for flavor-dependent deformed Lorentz transformations and an appropriate hierarchy of energy scales. If OPERA's result on a superluminal velocity of the muon-neutrino is confirmed, the model has a matching superluminal velocity of the corresponding charged lepton, the muon, at equal particle energy. Assuming that this model is not already ruled out, new TeV-scale effects in the muon sector are predicted. Also discussed is a different model with a superluminal sterile neutrino propagating in the usual 4 spacetime dimensions.

hep-ph↗
arXiv2012

Inflation and the cosmological constant

A particular compensation-type solution of the main cosmological constant problem has been proposed recently, with two massless vector fields dynamically canceling an arbitrary cosmological constant Λ. The naive expectation is that such a compensation mechanism does not allow for the existence of an inflationary phase in the very early Universe. However, it is shown that certain initial boundary conditions on the vector fields can in fact give rise to an inflationary phase.

gr-qc↗
arXiv2011

Superluminal neutrino and spontaneous breaking of Lorentz invariance

Generally speaking, the existence of a superluminal neutrino can be attributed either to re-entrant Lorentz violation at ultralow energy from intrinsic Lorentz violation at ultrahigh energy or to spontaneous breaking of fundamental Lorentz invariance (possibly by the formation of a fermionic condensate). Re-entrant Lorentz violation in the neutrino sector has been discussed elsewhere. Here, the focus is on mechanisms of spontaneous symmetry breaking.

hep-ph↗
arXiv2011

QCD-scale modified-gravity universe

A possible gluon-condensate-induced modified-gravity model with f(R) \propto |R|^{1/2} has been suggested previously. Here, a simplified version is presented using the constant flat-spacetime equilibrium value of the QCD gluon condensate and a single pressureless matter component (cold dark matter, CDM). The resulting dynamical equations of a spatially-flat and homogeneous Robertson-Walker universe are solved numerically. This simple empirical model allows, in fact, for a careful treatment of the boundary conditions and does not require a further scaling analysis as the original model did. Reliable predictions are obtained for several observable quantities of the homogeneous model universe. In addition, the estimator E_{G}, proposed by Zhang et al. to search for deviations from standard Einstein gravity, is calculated for linear sub-horizon matter-density perturbations. The QCD-scale modified-gravity prediction for E_{G}(z) differs from that of the LambdaCDM model by about \pm 10 % depending on the redshift z.

astro-ph.CO↗
arXiv2011

Models for low-energy Lorentz violation in the photon sector: Addendum to 'Consistency of isotropic modified Maxwell theory'

In a previous article [arXiv:1011.4258], we established the consistency of isotropic modified Maxwell theory for a finite range of the Lorentz-violating parameter \tilde{kappa}_{tr}, which includes both positive and negative values of \tilde{kappa}_{tr}. As an aside, we mentioned the existence of a physical model which, for low-energy photons, gives rise to isotropic modified Maxwell theory with a positive parameter \tilde{kappa}_{tr} (corresponding to a "slow" photon). Here, we present a related model which gives rise to isotropic modified Maxwell theory with a negative parameter \tilde{kappa}_{tr} (corresponding to a "fast" photon). Both models have an identical particle content, photon and Dirac particles, but differ in the type of spacetime manifold considered.

hep-th↗
arXiv2011

Entropic gravity, minimum temperature, and modified Newtonian dynamics

Verlinde's heuristic argument for the interpretation of the standard Newtonian gravitational force as an entropic force is generalized by the introduction of a minimum temperature (or maximum wave length) for the microscopic degrees of freedom on the holographic screen. With the simplest possible setup, the resulting gravitational acceleration felt by a test mass m from a point mass M at a distance R is found to be of the form of the modified Newtonian dynamics (MOND) as suggested by Milgrom. The corresponding MOND-type acceleration constant is proportional to the minimum temperature, which can be interpreted as the Unruh temperature of an emerging de-Sitter space. This provides a possible explanation of the connection between local MOND-type two-body systems and cosmology.

hep-th↗
arXiv2011

Superluminal muon-neutrino velocity from a Fermi-point-splitting model of Lorentz violation

A particular Fermi-point-splitting (FPS) model is proposed, which allows, for finite values of the three-momentum, the group and phase velocities of the muon-flavor neutrino in vacuum to be superluminal (i.e., muon-neutrino velocities greater than c, the velocity of light in vacuum). Still, the proposed FPS model has a front velocity equal to c for all particles, which is known to be crucial for causality. If the muon-neutrino velocity is indeed superluminal as claimed by OPERA, the model predicts that at least one of the other two flavors of neutrinos has a subluminal velocity.

hep-ph↗
arXiv2011

Dynamics of the quantum vacuum: Cosmology as relaxation to the equilibrium state

The behavior of the gravitating vacuum energy density in an expanding universe is discussed. A scenario is presented with a step-wise relaxation of the vacuum energy density. The vacuum energy density moves from plateau to plateau and follows, on average, the steadily decreasing matter energy density. The current plateau with a small positive value of the vacuum energy density (effective cosmological constant) may result from a still not equilibrated contribution of the light massive neutrinos to the quantum vacuum.

gr-qc↗
arXiv2011

Effective cosmological constant from TeV-scale physics: Simple field-theoretic model

Adopting the q-theory approach to the cosmological constant problem, a simple field-theoretic model is presented which generates an effective cosmological constant (remnant vacuum energy density) of the observed order of magnitude, Λ_{eff} \sim (meV)^4, if there exist new TeV-scale ultramassive particles with electroweak interactions. The model is simple, in the sense that it involves only a few types of fields and two energy scales, the gravitational energy scale E_{Planck}\sim 10^{15} TeV and the electroweak (new-physics) energy scale E_{ew}\sim 1-10 TeV.

hep-th↗
arXiv2011

Newtonian gravity as an entropic force: Towards a derivation of G

It has been suggested that the Newtonian gravitational force may emerge as an entropic force from a holographic microscopic theory. In this framework, the possibility is reconsidered that Newton's gravitational coupling constant G can be derived from the fundamental constants of the underlying microscopic theory.

hep-th↗
arXiv2011

Consistency of isotropic modified Maxwell theory: Microcausality and unitarity

The Lorentz-violating isotropic modified Maxwell theory minimally coupled to standard Dirac theory is characterized by a single real dimensionless parameter which is taken to vanish for the case of the standard (Lorentz-invariant) theory. A finite domain of positive and negative values of this Lorentz-violating parameter is determined, in which microcausality and unitarity hold. The main focus of this article is on isotropic modified Maxwell theory, but similar results for two anisotropic nonbirefringent cases are presented in the appendices.

hep-th↗
arXiv2011

Future limits on isotropic Lorentz violation in the photon sector from UHECRs and TeV gamma rays

Present and future ultra-high-energy-cosmic-ray facilities (e.g., the Pierre Auger Observatory with South and North components) and TeV-gamma-ray telescope arrays (e.g., HESS or VERITAS and CTA) have the potential to set stringent indirect bounds on the nine Lorentz-violating parameters of nonbirefringent modified Maxwell theory minimally coupled to standard Dirac theory. Theoretically, the most interesting case is isotropic Lorentz violation, which is described by a single parameter [taken to vanish for the standard Lorentz-invariant theory]. It appears possible to obtain in the future an upper (lower) indirect bound on this single isotropic Lorentz-violating parameter at the +10^{-21} (-10^{-17}) level. Comparison is made with existing and future direct bounds from laboratory experiments. The possible physics implications of upper bounds at the 10^{-21} level are discussed.

hep-ph↗
arXiv2010

Potential sensitivities to Lorentz violation from nonbirefringent modified Maxwell theory of Auger, HESS, and CTA

Present and future ultra-high-energy-cosmic-ray facilities (e.g., the South and North components of the Pierre Auger Observatory) and TeV-gamma-ray telescope arrays (e.g., HESS and CTA) have the potential to set stringent bounds on the nine Lorentz-violating parameters of nonbirefringent modified Maxwell theory minimally coupled to standard Dirac theory. A concrete example is given how to obtain, in the coming decennia, two-sided bounds on the eight anisotropic parameters at the 10^{-20} level and an upper (lower) bound on the single isotropic parameter at the +10^{-20} (-10^{-16}) level. Comparison is made with existing and potential direct bounds from laboratory experiments.

hep-ph↗
arXiv2010

Effective cosmological constant from TeV-scale physics

It has been suggested previously that the observed cosmological constant Lambda corresponds to the remnant vacuum energy density of dynamical processes taking place at a cosmic age set by the mass scale M \sim E_{ew} of ultramassive particles with electroweak interactions. Here, a simple modification of the nondissipative dynamic equations of q-theory is presented, which produces a remnant vacuum energy density (effective cosmological constant) of the correct order of magnitude. Combined with the observed value of Lambda, a first estimate of the required value of the energy scale E_{ew} ranges from 3 to 9 TeV, depending on the number of species of ultramassive particles and assuming a dissipative coupling constant of order unity. If correct, this estimate implies the existence of new TeV-scale physics beyond the standard model.

hep-ph↗
arXiv2010

Towards a solution of the cosmological constant problem

The standard model of elementary particle physics and the theory of general relativity can be extended by the introduction of a vacuum variable which is responsible for the near vanishing of the present cosmological constant (vacuum energy density). The explicit realization of this vacuum variable can be via a three-form gauge field, an aether-type velocity field, or any other field appropriate for the description of the equilibrium state corresponding to the Lorentz-invariant quantum vacuum. The extended theory has, without fine-tuning, a Minkowski-type solution of the field equations with spacetime-independent fields and provides, therefore, a possible solution of the main cosmological constant problem.

hep-th↗
arXiv2010

Gluon condensate, modified gravity, and the accelerating Universe

It has been suggested recently to study the dynamics of a gravitating gluon condensate q in the context of a spatially flat Friedmann-Robertson-Walker universe. The expansion of the Universe (or, more generally, the presence of a nonvanishing Ricci curvature scalar R) perturbs the gluon condensate and may induce a nonanalytic term \tilde{h}(R,q) in the effective gravitational action. The aim of this article is to explore the cosmological implications of a particular nonanalytic term \tilde{h} \propto η|R|^{1/2} |q|^{3/4}. With a quadratic approximation of the gravitating gluon-condensate vacuum energy density ρ_{V}(q) near the equilibrium value q_{0} and a small coupling constant ηof the modified-gravity term \tilde{h}, an "accelerating universe" is obtained which resembles the present Universe, both qualitatively and quantitatively. The unknown component X of this model universe (here, primarily due to modified-gravity effects) has an effective equation-of-state parameter \bar{w}_{X} which is found to evolve toward the value -1 from above.

gr-qc↗
arXiv2009

Lorentz violation and black-hole thermodynamics: Compton scattering process

A Lorentz-noninvariant modification of quantum electrodynamics (QED) is considered, which has photons described by the nonbirefringent sector of modified Maxwell theory and electrons described by the standard Dirac theory. These photons and electrons are taken to propagate and interact in a Schwarzschild spacetime background. For appropriate Lorentz-violating parameters, the photons have an effective horizon lying outside the Schwarzschild horizon. A particular type of Compton scattering event, taking place between these two horizons (in the photonic ergoregion) and ultimately decreasing the mass of the black hole, is found to have a nonzero probability. These events perhaps allow for a violation of the generalized second law of thermodynamics in the Lorentz-noninvariant theory considered.

hep-th↗