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On vacuum-energy decay from particle productionMay 31 2012Aug 02 2012A simplified (but consistent) description of particle-production backreaction effects in de Sitter spacetime is given.

New indirect bounds on Lorentz violation in the photon sectorOct 08 2008Oct 27 2008Direct laboratory bounds on the 9 nonbirefringent Lorentz-violating dimensionless parameters of modified-Maxwell theory range from the 10^{-7} level to the 10^{-16} level. The detection of air showers initiated by charged primaries (ultrahigh-energy cosmic-rays) ... More

Equilibrium boundary conditions, dynamic vacuum energy, and the Big BangMar 03 2008Oct 25 2008The near-zero value of the cosmological constant \Lambda in an equilibrium context may be due to the existence of a self-tuning relativistic vacuum variable q. Here, a cosmological nonequilibrium context is considered with a corresponding time-dependent ... More

CPT violation: mechanism and phenomenologyOct 15 2001Jul 22 2002A new mechanism for T and CPT violation is reviewed, which relies on chiral fermions, gauge interactions and nontrivial spacetime topology. Also discussed are the possible effects on the propagation of electromagnetic waves in vacuo, in particular for ... More

Small-Scale Structure of Spacetime: Bounds and ConjecturesOct 16 2007Nov 21 2007This review consists of two parts. The first part establishes certain astrophysical bounds on the smoothness of classical spacetime. Some of the best bounds to date are based on the absence of vacuum Cherenkov radiation in ultrahigh-energy cosmic rays. ... More

Emergent Relativity: Neutrinos as Probe of the Underlying TheoryDec 15 2006Neutrinos allow for a test of the hypothesis that the fermions of the Standard Model have Fermi-point splitting, analogous to the fermionic quasi-particles of certain condensed-matter systems. If present, the corresponding Lorentz-violating terms in the ... More

Z-string global gauge anomaly and Lorentz non-invarianceMay 15 1998Jan 05 1999Certain (3+1)-dimensional chiral non-Abelian gauge theories have been shown to exhibit a new type of global gauge anomaly, which in the Hamiltonian formulation is due to the fermion zero-modes of a Z-string-like configuration of the gauge potential and ... More

A regularized Big Bang singularityMar 25 2019Apr 08 2019Following-up on earlier work on the regularization of the singular Schwarzschild solution, we now apply the same procedure to the singular Friedmann solution. Specifically, we are able to remove the divergences of the Big Bang singularity, at the price ... More

Anomalous Lorentz and CPT violationSep 04 2017Oct 24 2018If there exists Lorentz and CPT violation in nature, then it is crucial to discover and understand the underlying mechanism. In this contribution, we discuss one such mechanism which relies on four-dimensional chiral gauge theories defined over a spacetime ... More

Standard Model Higgs field and energy scale of gravityFeb 06 2013Apr 25 2013The effective potential of the Higgs scalar field in the Standard Model may have a second degenerate minimum at an ultrahigh vacuum expectation value. This second minimum then determines, by radiative corrections, the values of the top-quark and Higgs-boson ... More

Dynamically broken Lorentz invariance from the Higgs sector?Feb 02 2012Mar 27 2012The original Abelian U(1) Higgs model in flat spacetime is enlarged by the addition of one real scalar with a particular potential. It is then shown that, while maintaining the original masses of the vector boson and Higgs scalar, there exists a time-dependent ... More

Superluminal muon-neutrino velocity from a Fermi-point-splitting model of Lorentz violationSep 26 2011Oct 03 2011A 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, ... More

UHECR bounds on Lorentz violation in the photon sectorJul 14 2008Oct 14 2008The aim of this brief review is to present a case study of how astrophysics data can be used to get bounds on Lorentz-violating parameters. For this purpose, a particularly simple Lorentz-violating modification of the Maxwell theory of photons is considered, ... More

Neutrino oscillations from the splitting of Fermi pointsMar 29 2004Jul 19 2004As was shown previously, oscillations of massless neutrinos may be due to the splitting of multiply degenerate Fermi points. In this Letter, we give the details and propose a three-flavor model of Fermi point splittings and neutrino mixings with only ... More

New Electroweak Instanton and Possible Breakdown of UnitaritySep 16 1994Potential implications of a new constrained instanton solution in the electroweak standard model are discussed. Notably, there may be a non-perturbative unitarity violating contribution to the total cross-section at high collision energies.

Existence of a New Instanton in Constrained Yang-Mills-Higgs TheoryJun 02 1993Our goal is to discover possible new 4-dimensional euclidean solutions (instantons) in fundamental SU(2) Yang-Mills-Higgs theory, with a constraint added to prevent collapse of the scale. We show that, most likely, there exists one particular new constrained ... More

Lorentz-violating neutral-pion decays in isotropic modified Maxwell theoryOct 11 2016Oct 27 2016We consider an extension of the Standard Model with isotropic nonbirefringent Lorentz violation in the photon sector and specialize to the case of a "fast" photon with a phase velocity larger than the maximum attainable velocity of the fermions. With ... More

A regularized Big Bang singularityMar 25 2019May 07 2019Following-up on earlier work on the regularization of the singular Schwarzschild solution, we now apply the same procedure to the singular Friedmann solution. Specifically, we are able to remove the divergences of the Big Bang singularity, at the price ... More

Nonsingular bounce revisitedJul 15 2019Aug 22 2019The big bang singularity of the expanding-universe Friedmann solution of the Einstein gravitational field equation can be regularized by the introduction of a nonzero length scale $b$. The result is a nonsingular bounce of the cosmic scale factor $a(T)$ ... More

Skyrmion spacetime defectFeb 27 2014Jul 02 2014A finite-energy static classical solution is obtained for standard Einstein gravity coupled to an $SO(3)\times SO(3)$ chiral model of scalars [a Skyrme model]. This nonsingular localized solution has nontrivial topology for both the spacetime manifold ... More

Black-hole solution without curvature singularityApr 08 2013Sep 05 2013An exact solution of the vacuum Einstein field equations over a nonsimply-connected manifold is presented. This solution is spherically symmetric and has no curvature singularity. It can be considered to be a regularization of the Schwarzschild solution ... More

Entropic-gravity derivation of MONDJan 19 2012Apr 04 2012A heuristic entropic-gravity derivation has previously been given of the gravitational two-body force of modified Newtonian dynamics (MOND). Here, it is shown that also another characteristic of MOND can be recovered, namely, the external field effect ... More

Potential sensitivities to Lorentz violation from nonbirefringent modified Maxwell theory of Auger, HESS, and CTAAug 11 2010Nov 24 2010Present 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 ... More

A CPT anomalyDec 19 1999Jun 16 2000We consider chiral gauge theories defined over a four-dimensional spacetime manifold with a Cartesian product structure for at least one compact spatial dimension. For a simple setup, we calculate the effective gauge field action by integrating out the ... More

Effective cosmological constant from TeV-scale physics: Simple field-theoretic modelJan 06 2011Jul 27 2011Adopting 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, \Lambda_{eff} \sim ... More

Newtonian gravity as an entropic force: Towards a derivation of GJun 10 2010May 05 2011It 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 ... More

Effective cosmological constant from TeV-scale physicsJan 12 2010Oct 20 2010It 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 ... More

Another Look at the Electroweak Vortex SolutionJun 07 1994We discuss the position in configuration space of the electroweak vortex solution. (Talk given at the NATO Advanced Research Workshop "Electroweak Physics and the Early Universe", Sintra, Portugal, March 1994)

A regularized Big Bang singularityMar 25 2019Following-up on earlier work on the regularization of the singular Schwarzschild solution, we now apply the same procedure to the singular Friedmann solution. Specifically, we are able to remove the divergences of the Big Bang singularity, at the price ... More

Lorentz-violating neutral-pion decays in isotropic modified Maxwell theoryOct 11 2016We consider an extension of the Standard Model with isotropic nonbirefringent Lorentz violation in the photon sector and specialize to the case of a "fast" photon with a phase velocity larger than the maximum attainable velocity of the fermions. With ... More

QCD-scale modified-gravity universeMay 17 2010Dec 16 2011A 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 ... More

Fermion zero-modes of a new constrained instanton in Yang-Mills-Higgs theorySep 26 1997Apr 05 1998Self-consistent Ansaetze are presented for the left- and right-handed isodoublet fermion zero-modes of the constrained instanton Istar in the vacuum sector of euclidean SU(2) Yang-Mills-Higgs theory. These left- and right-handed fermion wave functions ... More

Electroweak defectsDec 17 1996Jan 21 1998A brief, non-technical review is given of certain defect-like configurations in the electroweak standard model, which may have played an important role in the physics of the early universe.

Ultraheavy particles at the LHC or a next-generation collider?Mar 12 2015Aug 31 2015If the effective cosmological constant $\Lambda$ of the present universe is due to physical processes in the early universe operating at temperatures just above the electroweak energy scale, it is possible that new particles with multi-$\text{TeV}$ masses ... More

Neutrino mass and the Standard ModelDec 12 2011Jan 31 2013It is pointed out (not for the first time) that the minimal Standard Model, without additional gauge-singlet right-handed neutrinos or isotriplet Higgs fields, allows for nonvanishing neutrino masses and mixing. The required interaction term is nonrenormalizable ... More

Superluminal neutrino, flavor, and relativityOct 10 2011Jan 23 2012Modified 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 ... More

Construction of a New Electroweak SphaleronJun 21 1993We present a self-consistent ansatz for a new sphaleron in the electroweak standard model. The resulting field equations are solved numerically. This sphaleron sets the height of the energy barrier for the global SU(2) anomaly.

Black-hole solution without curvature singularity and closed timelike curvesMay 13 2013Feb 01 2014With a prescribed Coulomb-type energy-momentum tensor, an exact solution of the Einstein field equations over a nonsimply-connected manifold is presented. This spherically symmetric solution has neither curvature singularities nor closed timelike curves. ... More

Gluon condensate, modified gravity, and the accelerating UniverseApr 21 2009Feb 10 2010It 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 ... More

Fundamental length scale of quantum spacetime foamMar 01 2007Aug 29 2007It is argued that the fundamental length scale for the quantum dynamics of spacetime need not be equal to the Planck length. Possibly, this new length scale is related to a nonvanishing cosmological constant or vacuum energy density.

Electroweak baryon number violationSep 19 2002Oct 28 2002Electroweak baryon number violation may play a crucial role for the creation of the matter-antimatter asymmetry in the early universe. In this talk, we review the basic mechanism, which relies on the behavior of chiral fermions in nontrivial Yang-Mills ... More

A generalization of unimodular gravity with vacuum-matter energy exchangeApr 11 2016Jun 13 2016An effective theory of gravity in the infrared is proposed, which involves the determinant of the metric relative to the determinant of a prior metric taken to be that of Minkowski spacetime. This effective theory can be interpreted as a generalization ... More

A new type of nonsingular black-hole solution in general relativitySep 26 2013May 31 2014Certain exact solutions of the Einstein field equations over nonsimply-connected manifolds are reviewed. These solutions are spherically symmetric and have no curvature singularity. They provide a regularization of the standard Schwarzschild solution ... More

Gravity Without Curved Spacetime: A Simple CalculationAug 15 2012Sep 06 2012Classical-particle trajectories are calculated for the static Einstein universe without requiring that the 3-space be closed and curved. Freely-moving test particles are found to return to their starting positions because of strong gravitational-field ... More

Spontaneously broken Lorentz invariance from the dynamics of a heavy sterile neutrinoNov 21 2011Jul 10 2012A relativistic theory for neutrino superluminality is presented (in principle, the same mechanism applies also to other fermions). The theory involves the standard-model particles and one additional heavy sterile neutrino with an energy-scale close to ... More

Inflation and the cosmological constantJul 20 2011Jan 10 2012A 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 \Lambda. The naive expectation is that such a compensation ... More

Future limits on isotropic Lorentz violation in the photon sector from UHECRs and TeV gamma raysMar 08 2011Mar 15 2011Present 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 ... More

Newton's gravitational coupling constant from a quantum of areaJan 27 2011Feb 19 2012A previous calculation of Newton's gravitational coupling constant G is generalized. This generalization makes it possible to have "atoms of two-dimensional space" with an integer dimension d_{atom} of the internal space, where the case d_{atom}=1 is ... More

Lorentz invariance, vacuum energy, and cosmologyOct 09 2008Nov 11 2008This contribution reviews recent work on a new approach to the cosmological constant problem, which starts from the macroscopic behavior of a conserved relativistic microscopic variable q. First, the statics of the vacuum energy density is discussed and, ... More

Fundamental time asymmetry from nontrivial space topologyNov 26 2001Aug 12 2002It is argued that a fundamental time asymmetry could arise from the global structure of the space manifold. The proposed mechanism relies on the CPT anomaly of certain chiral gauge theories defined over a multiply connected space manifold. The resulting ... More

A regularized Big Bang singularityMar 25 2019Mar 27 2019Following-up on earlier work on the regularization of the singular Schwarzschild solution, we now apply the same procedure to the singular Friedmann solution. Specifically, we are able to remove the divergences of the Big Bang singularity, at the price ... More

Nonsingular bounce revisitedJul 15 2019The big bang singularity of the Friedmann solution for an expanding universe can be regularized by the introduction of a nonzero length scale $b$. The result is a nonsingular bounce of the cosmic scale factor $a(T)$ with a contracting pre-bounce phase ... More

Nonsingular bounce revisitedJul 15 2019Jul 24 2019The big bang singularity of the Friedmann solution for an expanding universe can be regularized by the introduction of a nonzero length scale $b$. The result is a nonsingular bounce of the cosmic scale factor $a(T)$ with a contracting pre-bounce phase ... More

Nonsingular bounce revisitedJul 15 2019Aug 01 2019The big bang singularity of the Friedmann solution for an expanding universe can be regularized by the introduction of a nonzero length scale $b$. The result is a nonsingular bounce of the cosmic scale factor $a(T)$ with a contracting pre-bounce phase ... More

Comparison of spacetime defects which are homeomorphic but not diffeomorphicApr 10 2014Nov 25 2014Certain remnants of a quantum spacetime foam can be modeled by a distribution of defects embedded in a flat classical spacetime. The presence of such spacetime defects affects the propagation of elementary particles. In this article, we show explicitly ... More

Entropic gravity, minimum temperature, and modified Newtonian dynamicsApr 11 2011Nov 24 2011Verlinde'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 ... More

A nonsingular spacetime defectMar 28 2013Apr 18 2014A nonsingular localized static classical solution is constructed for standard Einstein gravity coupled to an $SO(3)\times SO(3)$ chiral model of scalars (Skyrme model). This solution corresponds to a spacetime defect and its construction proceeds in three ... More

Bounds on length scales of classical spacetime foam modelsOct 17 2006Jan 24 2007Simple models of a classical spacetime foam are considered, which consist of identical static defects embedded in Minkowski spacetime. Plane-wave solutions of the vacuum Maxwell equations with appropriate boundary conditions at the defect surfaces are ... More

Comment on "Vacuum Photon Splitting in Lorentz-Violating Quantum Electrodynamics"Dec 11 2003It has been argued in hep-ph/0212382 that there may be observable effects from photon triple splitting in an extended version of quantum electrodynamics with Lorentz violation in the fermion sector. The argument is based on an analogy with photon splitting ... More

Sphalerons, spectral flow, and anomaliesApr 20 2003Jul 07 2003The topology of configuration space may be responsible in part for the existence of sphalerons. Here, sphalerons are defined to be static but unstable finite-energy solutions of the classical field equations. Another manifestation of the nontrivial topology ... More

Maxwell-Chern-Simons theory for curved spacetime backgroundsJul 16 2005Nov 29 2008We consider a modified version of four-dimensional electrodynamics, which has a photonic Chern-Simons-like term with spacelike background vector in the action. Light propagation in curved spacetime backgrounds is discussed using the geometrical-optics ... More

Consistency of isotropic modified Maxwell theory: Microcausality and unitarityNov 18 2010Apr 03 2011The 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 ... More

Vacuum Cherenkov radiation in spacelike Maxwell-Chern-Simons theoryApr 24 2007Jul 23 2007A detailed analysis of vacuum Cherenkov radiation in spacelike Maxwell-Chern-Simons (MCS) theory is presented. A semiclassical treatment reproduces the leading terms of the tree-level result from quantum field theory. Moreover, certain quantum corrections ... More

Reconsidering a higher-spin-field solution to the main cosmological constant problemJul 05 2011Apr 02 2012Following an earlier suggestion by Dolgov, we present a specific model of two massless vector fields which dynamically cancel a cosmological constant of arbitrary magnitude and sign. Flat Minkowski spacetime appears asymptotically as an attractor of the ... More

Addendum: Ultrahigh-energy cosmic-ray bounds on nonbirefringent modified-Maxwell theoryJun 26 2008Nonbirefringent modified-Maxwell theory, coupled to standard Dirac particles, involves nine dimensionless parameters, which can be bounded by the inferred absence of vacuum Cherenkov radiation for ultrahigh-energy cosmic rays (UHECRs). With selected UHECR ... More

Classical stability of higher-derivative q-theory in the four-form-field-strength realizationApr 18 2017Jun 02 2017We show that higher-derivative $q$-theory in the four-form-field-strength realization does not suffer from the Ostrogradsky instability at the classical level.

A New Perspective on Electroweak StringsFeb 02 1994The vortex solution (Z-string) of the electroweak interactions can be interpreted as the 2-dimensional sphaleron at the top of a non-contractible sphere. The same holds for another type of solution, the W-string.

Possible solution to the main cosmological constant problemSep 22 2011May 09 2012A modified-gravity-type model of two hypothetical massless vector fields is presented. These vector fields are gravitationally coupled to standard matter and an effective cosmological constant. Considered in a cosmological context, the vector fields dynamically ... More

New two-sided bound on the isotropic Lorentz-violating parameter of modified Maxwell theorySep 18 2008Oct 25 2008There is a unique Lorentz-violating modification of the Maxwell theory of photons, which maintains gauge invariance, CPT, and renormalizability. Restricting the modified-Maxwell theory to the isotropic sector and adding a standard spin-one-half Dirac ... More

CPT anomaly in two-dimensional chiral U(1) gauge theoriesJun 20 2000Apr 10 2001The CPT anomaly, which was first seen in perturbation theory for certain four-dimensional chiral gauge theories, is also present in the exact result for a class of two-dimensional chiral U(1) gauge theories on the torus. Specifically, the chiral determinant ... More

Photon decay in a CPT-violating extension of quantum electrodynamicsDec 03 2002Apr 07 2003We consider the process of photon decay in quantum electrodynamics with a CPT-violating Chern-Simons-like term added to the action. For a simplified model with only the quadratic Maxwell and Chern-Simons-like terms and the quartic Euler-Heisenberg term, ... More

Causality and CPT violation from an Abelian Chern-Simons-like termJan 09 2001Jun 02 2001We study a class of generalized Abelian gauge field theories where CPT symmetry is violated by a Chern-Simons-like term which selects a preferred direction in spacetime. Such Chern-Simons-like terms may either emerge as part of the low-energy effective ... More

A global anomaly from the Z-stringFeb 03 1997Apr 16 1997The response of isodoublet fermions to classical backgrounds of essentially 2-dimensional boson fields in SU(2) Yang-Mills-Higgs theory is investigated. In particular, the spectral flow of Dirac eigenvalues is calculated for a non-contractible sphere ... More

Construction of a new constrained instanton in Yang-Mills-Higgs theoryJun 29 1996Feb 23 1997A self-consistent ansatz is presented for a four-dimensional euclidean solution (instanton) in the vacuum sector of constrained SU(2) Yang-Mills-Higgs theory.

De-Sitter-spacetime instability from a nonstandard vector fieldApr 23 2012Jul 13 2012It is found that de-Sitter spacetime, the constant-curvature matter-free solution of the Einstein equations with a positive cosmological constant, becomes classically unstable due to the dynamic effects of a certain type of vector field (fundamentally ... More

Vector-field model with compensated cosmological constant and radiation-dominated FRW phaseAug 09 2011Apr 12 2012A special model of a massless vector-field is presented, which has an extra modified-gravity-type interaction term in the action. The cosmology of the model is studied with standard noninteracting relativistic matter added. It is found that this cosmology ... More

Models for low-energy Lorentz violation in the photon sector: Addendum to 'Consistency of isotropic modified Maxwell theory'Oct 18 2011Dec 15 2011In 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}. ... More

Vacuum Cherenkov radiation and photon triple-splitting in a Lorentz-noninvariant extension of quantum electrodynamicsAug 10 2005Dec 29 2005We consider a CPT-noninvariant scalar model and a modified version of quantum electrodynamics with an additional photonic Chern-Simons-like term in the action. In both cases, the Lorentz violation traces back to a spacelike background vector. The effects ... More

A sphaleron for the non-Abelian anomalyOct 19 2004Feb 09 2005A self-consistent Ansatz for a new sphaleron of SU(3) Yang-Mills-Higgs theory is presented. With a single triplet of Weyl fermions added, there exists, most likely, one pair of fermion zero modes, which is known to give rise to the non-Abelian (Bardeen) ... More

Spacetime foam, CPT anomaly, and photon propagationDec 02 2003Sep 04 2004The CPT anomaly of certain chiral gauge theories has been established previously for flat multiply connected spacetime manifolds M of the type R^3 x S^1, where the noncontractible loops have a minimal length. In this article, we show that the CPT anomaly ... More

Ultrahigh-energy cosmic-ray bounds on nonbirefringent modified-Maxwell theorySep 16 2007Jun 27 2008A particularly simple Lorentz-violating modification of the Maxwell theory of photons maintains gauge invariance, CPT, and renormalization. This modified-Maxwell theory, coupled to standard Dirac particles, involves nineteen dimensionless "deformation ... More

Torsion, topology and CPT anomaly in two-dimensional chiral U(1) gauge theoryMay 30 2001Sep 07 2001We consider the CPT anomaly of two-dimensional chiral U(1) gauge theory on a torus with topologically nontrivial zweibeins corresponding to the presence of spacetime torsion. The resulting chiral determinant can be expressed in terms of the standard chiral ... More

Model for a time-symmetric Milne-like universe without big bang curvature singularitySep 12 2019We present a physics model for a time-symmetric Milne-like universe based on the $q$-theory approach to the cosmological constant problem, supplemented by an assumed vacuum-matter energy exchange possibly due to quantum-dissipative effects. Without fine-tuning ... More

Causality and radiatively induced CPT violationMay 03 2001May 31 2001We consider quantum electrodynamics with an additional Lorentz- and CPT-violating axial-vector term in the fermionic sector and discuss the possibility that radiative corrections induce a Lorentz- and CPT-violating Chern-Simons-like term for the gauge ... More

Spacetime foam and high-energy photonsNov 09 2005Dec 02 2010It is shown that high-energy astrophysics can provide information on the small-scale structure of spacetime.

Photon-propagation model with random background field: Length scales and Cherenkov limitsJun 07 2005Aug 01 2005We present improved experimental bounds on typical length scales of a photon-propagation model with a frozen (time-independent) random background field, which could result from anomalous effects of a static, multiply connected spacetime foam.

Fermions with a bounded and discrete mass spectrumDec 02 2014Feb 23 2015A mechanism for determining fermion masses in four spacetime dimensions is presented, which uses a scalar-field domain wall extending in a fifth spacelike dimension and a special choice of Yukawa coupling constants. A bounded and discrete fermion mass ... More

CPT anomaly: a rigorous result in four dimensionsMay 05 2002Aug 19 2002The existence of a CPT anomaly is established for a particular four-dimensional Abelian lattice gauge theory with Ginsparg-Wilson fermions.

Parton-model calculation of a nonstandard decay process in isotropic modified Maxwell theoryApr 06 2015Jul 02 2015We have performed a calculation in the parton-model approximation of a nonstandard decay process in isotropic modified Maxwell theory coupled to standard Dirac theory, with a single Lorentz-violating parameter $\kappa$ in the photonic sector. Previous ... More

Coexisting vacua and effective gravityMar 21 2005Nov 19 2005Our Universe may be a domain separated by physical phase boundaries from other domain-Universes with different vacuum energy density and matter content. The coexistence of different quantum vacua is perhaps regulated by the exchange of global fermionic ... More

Vacuum energy density kicked by the electroweak crossoverMay 12 2009Oct 01 2009Using q-theory, we show that the electroweak crossover can generate a remnant vacuum energy density \Lambda \sim E_{ew}^8 / E_{planck}^4, with effective electroweak energy scale E_{ew} \sim 10^{3} GeV and reduced Planck-energy scale E_{planck} \sim 10^{18} ... More

Merging gauge coupling constants without Grand UnificationMay 05 2005May 13 2005The merging of the running couplings constants of the weak, strong, and electromagnetic fields does not require the unification of these gauge fields at high energy. It can, in fact, be the property of a general fermionic system in which gauge bosons ... More

Quantum phase transition for the BEC--BCS crossover in condensed matter physics and CPT violation in elementary particle physicsJul 22 2004Nov 04 2004We discuss the quantum phase transition that separates a vacuum state with fully-gapped fermion spectrum from a vacuum state with topologically-protected Fermi points (gap nodes). In the context of condensed-matter physics, such a quantum phase transition ... More

Dynamic vacuum variable and equilibrium approach in cosmologyJun 17 2008Sep 18 2008A modified-gravity theory is considered with a four-form field strength F, a variable gravitational coupling parameter G(F), and a standard matter action. This theory provides a concrete realization of the general vacuum variable q as the four-form amplitude ... More

Dynamics of the quantum vacuum: Cosmology as relaxation to the equilibrium stateFeb 15 2011Oct 01 2011The 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, ... More

Gluonic vacuum, q-theory, and the cosmological constantNov 26 2008Mar 28 2009In previous work, q-theory was introduced to describe the gravitating macroscopic behavior of a conserved microscopic variable q. In this article, the gluon condensate of quantum chromodynamics is considered in terms of q-theory. The remnant vacuum energy ... More

Propagating q-field and q-ball solutionSep 12 2016Sep 19 2016One possible solution of the cosmological constant problem involves a so-called $q$-field, which self-adjusts so as to give a vanishing gravitating vacuum energy density (cosmological constant) in equilibrium. We show that this $q$-field can manifest ... More

Nonsingular bounce cosmology from general relativityApr 22 2019We investigate a particular classical nonsingular bounce cosmology, which results from general relativity if we allow for degenerate metrics. The simplest model has a constant equation of state and we calculate the modified Hubble diagram for both the ... More

Dark matter from dark energy in q-theoryDec 04 2016Mar 20 2017A constant (spacetime-independent) $q$-field may play a crucial role for the cancellation of Planck-scale contributions to the gravitating vacuum energy density. We now show that a small spacetime-dependent perturbation of the equilibrium $q$-field behaves ... More

Asymmetric nonsingular bounce from a dynamic scalar fieldJun 11 2019Aug 15 2019We present a dynamical model for a time-asymmetric nonsingular bounce with a post-bounce change of the effective equation-of-state parameter. Specifically, we consider a scalar-field model with a time-reversal-noninvariant effective potential.