Search

Lorentz- and CPT-violating effects initiating two-body electromagnetic flavor-changing decays of charged leptons are studied in the framework of Lorentz-violating effective field theory. An analysis of data from experiments at the Paul Scherrer Institute and at the Stanford Linear Accelerator measuring the branching ratios of these decays provides 576 constraints on independent flavor-changing effects in the charged-lepton sector, consistent with no Lorentz and CPT violation at the level of parts in 10−13–10−9 GeV−1.

Many effective field theories describing gravity cannot arise from an underlying theory based on Riemann geometry or its extensions to include torsion and nonmetricity but may instead emerge from another geometry or may have a nongeometric basis. The Lagrange density for a broad class of such theories is investigated. The action for fermions coupled to gravity is linearized about a Minkowski background and is found to include terms describing small deviations from Lorentz invariance and gravitational gauge invariance. The corresponding nonrelativistic hamiltonian is derived at second order in the fermion momentum. The implications for laboratory experiments and astrophysical observations with fermions are studied, with primary focus on anomalous spin-gravity couplings. First constraints on some coefficients are extracted from existing data obtained via measurements at different potentials, comparisons of gravitational accelerations, interferometric methods, and investigations of gravitational bound states. Some prospects for future experimental studies are discussed., 24 pages two-column REVTeX, version accepted in Physical Review D

We propose a correspondence between the description of emergent Lorentz symmetry in condensed-matter systems and the established general effective field theory for Lorentz violation in fundamental theories of spacetime and matter. This correspondence has potential implications in both directions. We illustrate the proposal by investigating its consequences for the spectral and transport properties of Dirac and Weyl semimetals. Particular realizations of this framework give rise to Dirac nodal spectra with nodal lines and rings. We demonstrate a bulk-boundary correspondence between bulk topological invariants and drumhead surface states of these Dirac nodal semimetals. We calculate their transport coefficients in leading-order perturbation theory, thereby characterizing the unconventional electromagnetic response due to small deviations from emergent Lorentz invariance. Some prospective future applications of the correspondence are outlined., Comment: 18 pages, 7 figures. We welcome all feedback!

Effective field theories describing gravity coupled to matter are investigated, allowing for operators of arbitrary mass dimension. Terms violating local Lorentz and diffeomorphism invariance while preserving internal gauge symmetries are included. The theoretical framework for violations of local Lorentz and diffeomorphism invariance and associated conceptual issues are discussed, including transformations in curved and approximately flat spacetimes, the treatment of various types of backgrounds, the implications of symmetry breaking, and the no-go constraints for explicit violation in Riemann geometry. Techniques are presented for the construction of effective operators, and the possible terms in the gravity, gauge, fermion, and scalar sectors are classified and enumerated. Explicit expressions are obtained for terms containing operators of mass dimension six or less in the effective action for General Relativity coupled to the Standard Model of particle physics. Special cases considered include Einstein-Maxwell effective field theories and the limit with only scalar coupling constants., Comment: 36 pages two-column REVTeX

The correspondence between Riemann-Finsler geometries and effective field theories with spin-independent Lorentz violation is explored. We obtain the general quadratic action for effective scalar field theories in any spacetime dimension with Lorentz-violating operators of arbitrary mass dimension. Classical relativistic point-particle lagrangians are derived that reproduce the momentum-velocity and dispersion relations of quantum wave packets. The correspondence to Finsler structures is established, and some properties of the resulting Riemann-Finsler spaces are investigated. The results provide support for open conjectures about Riemann-Finsler geometries associated with Lorentz-violating field theories., Comment: 9 pages, version published in Physics Letters B

The effects of quark-sector Lorentz violation on deep inelastic electron-proton scattering are studied. We show that existing data can be used to establish first constraints on numerous coefficients for Lorentz violation in the quark sector at an estimated sensitivity of parts in a million., Comment: 8 pages, version published in Physics Letters B

The Newton limit of gravity is studied in the presence of Lorentz-violating gravitational operators of arbitrary mass dimension. The linearized modified Einstein equations are obtained and the perturbative solutions are constructed and characterized. We develop a formalism for data analysis in laboratory experiments testing gravity at short range and demonstrate that these tests provide unique sensitivity to deviations from local Lorentz invariance., Comment: 7 pages

A framework is presented for the factorization of high-energy hadronic processes in the presence of Lorentz and CPT violation. The comprehensive effective field theory describing Lorentz and CPT violation, the Standard-Model Extension, is used to demonstrate factorization of the hadronic tensor at leading order in electroweak interactions for deep inelastic scattering and for the Drell-Yan process. Effects controlled by both minimal and nonminimal coefficients for Lorentz violation are explored, and the equivalent parton-model description is derived. The methodology is illustrated by determining cross sections and studying estimated attainable sensitivities to Lorentz violation using real data collected at the Hadronen-Elektronen Ring Anlage and the Large Hadron Collider and simulated data for the future US-based electron-ion collider., Comment: 43 pages, version published in JHEP

Spacetime nonmetricity can be studied experimentally through its couplings to fermions and photons. We use recent high-precision searches for Lorentz violation to deduce first constraints involving the 40 independent nonmetricity components down to levels of order $10^{-43}$ GeV., Comment: 13 pages

The prospects are explored for testing Lorentz and CPT symmetry in the top-quark sector. We present the relevant Lagrange density, discuss physical observables, and describe the signals to be sought in experiments. For top-antitop pair production via quark or gluon fusion with subsequent semileptonic or hadronic decays, we obtain the matrix element in the presence of Lorentz violation using the narrow-width approximation. The issue of testing CPT symmetry in the top-quark sector is also addressed. We demonstrate that single-top production and decay is well suited to a search for CPT violation, and we present the matrix elements for single-top production in each of the four tree-level channels. Our results are applicable to searches for Lorentz violation and studies of CPT symmetry in collider experiments, including notably high-statistics top-antitop and single-top production at the Large Hadron Collider., 16 pages two-column REVTeX

A general framework for tests of Lorentz invariance with electromagnetic waves is presented, allowing for operators of arbitrary mass dimension. Signatures of Lorentz violations include vacuum birefringence, vacuum dispersion, and anisotropies. Sensitive searches for violations using sources such as active galaxies, gamma-ray bursts, and the cosmic microwave background are discussed. Direction-dependent dispersion constraints are obtained on operators of dimension 6 and 8 using gamma-ray bursts and the blazar Markarian 501. Stringent constraints on operators of dimension 3 are found using 5-year data from the Wilkinson Microwave Anisotropy Probe. No evidence appears for isotropic Lorentz violation, while some support at one sigma is found for anisotropic violation., Comment: 4 pages two-column ApJ format

Comparatively few searches have been performed for violations of local Lorentz invariance in the pure-gravity sector. We show that tests of short-range gravity are sensitive to a broad class of unconstrained and novel signals that depend on the experimental geometry and on sidereal time., Comment: 6 pages two-column REVTeX, version published in Physical Review D

Violations of Lorentz invariance can lead to an energy-dependent vacuum dispersion of light, which results in arrival-time differences of photons arising with different energies from a given transient source. In this work, direction-dependent dispersion constraints are obtained on nonbirefringent Lorentz-violating effects, using the observed spectral lags of the gamma-ray burst GRB 160625B. This burst has unusually large high-energy photon statistics, so we can obtain constraints from the true spectral time lags of bunches of high-energy photons rather than from the rough time lag of a single highest-energy photon. Also, GRB 160625B is the only burst to date having a well-defined transition from positive lags to negative lags, which provides a unique opportunity to distinguish Lorentz-violating effects from any source-intrinsic time lag in the emission of photons of different energy bands. Our results place comparatively robust two-sided constraints on a variety of isotropic and anisotropic coefficients for Lorentz violation, including first bounds on Lorentz-violating effects from operators of mass dimension ten in the photon sector., 6 pages, 3 figures, 1 table. Accepted for publication in ApJ

The recent observation of high-energy astrophysical neutrinos can be used to constrain violations of Lorentz invariance emerging from a quantum theory of gravity. We perform threshold and Cherenkov analyses that improve existing bounds by factors ranging from about a million to 10^{20}., 5 pages two-column REVTeX

A search for sidereal variations in the force between two planar tungsten oscillators separated by about 80 microns sets the first experimental limits on Lorentz violation involving quadratic couplings of the Riemann curvature, consistent with no effect at the level of $10^{-7}$ m$^2$., Comment: 13 pages

Spontaneous CPT breaking arising in string theory has been suggested as a possible observable experimental signature in neutral-meson systems. We provide a theoretical framework for the treatment of low-energy effects of spontaneous CPT violation and the attendant partial Lorentz breaking. The analysis is within the context of conventional relativistic quantum mechanics and quantum field theory in four dimensions. We use the framework to develop a CPT-violating extension to the minimal standard model that could serve as a basis for establishing quantitative CPT bounds., Comment: accepted in Phys. Rev. D; scheduled for June 1997

The theoretical description of fermions in the presence of Lorentz and CPT violation is developed. We classify all Lorentz- and CPT-violating and invariant terms in the quadratic Lagrange density for a Dirac fermion, including operators of arbitrary mass dimension. The exact dispersion relation is obtained in closed and compact form, and projection operators for the spinors are derived. The Pauli hamiltonians for particles and antiparticles are extracted, and observable combinations of operators are identified. We characterize and enumerate the coefficients for Lorentz violation for any operator mass dimension via a decomposition using spin-weighted spherical harmonics. The restriction of the general theory to various special cases is presented, including isotropic models, the nonrelativistic and ultrarelativistic limits, and the minimal Standard-Model Extension. Expressions are derived in several limits for the fermion dispersion relation, the associated fermion group velocity, and the fermion spin-precession frequency. We connect the analysis to some other formalisms and use the results to extract constraints from astrophysical observations on isotropic ultrarelativistic spherical coefficients for Lorentz violation., Comment: 29 pages two-column REVTeX

In some quantum theories of gravity, deviations from the laws of relativity could be comparatively large while escaping detection to date. In the neutrino sector, precision experiments with beta decay yield new and improved constraints on these countershaded relativity violations. Existing data are used to extract bounds of $3 \times 10^{-8}$ GeV on the magnitudes of two of the four possible coefficients, and estimates are provided of future attainable sensitivities in a variety of experiments., Comment: 5 pages two-column REVTeX, version published in Rapid Communications, Physical Review D

We investigate the issue of testing {ital CPT} invariance in the neutral-{ital D} system, using {ital D} events obtained either from fixed-target experiments or from a {tau}-charm factory. For both types of experiments we show that the expected suppression of mixing in the {ital D} system, normally viewed as a disadvantage for {ital CP} tests, allows unsuppressed measurement of certain parameters describing {ital CPT} violation. Asymmetries are presented that permit the extraction of parameters for direct {ital CPT} violation in the {ital D} system and for indirect {ital CPT} violation in the {ital K} system. We also show that experiments on the neutral-{ital D} system provide an alternative means for measuring conventional indirect {ital T} violation in the kaon system.

A class of calculable global models for neutrino oscillations based on Lorentz and CPT violation is presented. One simple example matches established neutrino data from accelerator, atmospheric, reactor, and solar experiments, using only two degrees of freedom instead of the usual five. A third degree of freedom appears in the model, and it naturally generates the MiniBooNE low-energy anomalies. More involved models in this class can also accommodate the LSND anomaly and neutrino-antineutrino differences of the MINOS type. The models predict some striking signals in various ongoing and future experiments., 17 pages two-column REVTeX

We discuss the possibility that the issue of spacetime singularities in general relativity is solved by their stringy extensions.

Nuclear simulations of neutrino oscillations in the early Universe are performed for a neutrino-mass hierarchy with the vacuum mass of the second neutrino exceeding that of the first. This situation is equivalent to a normal hierarchy with mixing angle greater than π 4 . We find that a large conversion of electron neutrinos to muon neutrinos occurs, independent of mixing angle. For certain parameter values, this is caused by the MSW effect. In the rest of the parameter region a new mechanism is operative, arising from nonlinear effects involving neutrino-neutrino forward scattering. This nonlinear conversion mechanism causes substantial flavor oscillation even for extremely small mixing angles.

Proposed close-encounter solar probes (Vulcan and Solar Probe) are planned to have highly eccentric orbits, with a perihelion of about $4R_S$ and an inclination close to $90^\circ$ out of the plane of the ecliptic. We show this could allow at least an order-of-magnitude improvement in the present directly measured limit on the photon mass., Comment: 7 pages, LaTeX, Indiana University preprint IUHET 245 and Los Alamos Preprint LA-UR-93-1128

Numerical studies are performed for neutrino oscillations for t > 1 3 seconds after the big bang. The effects of electron, positron and neutrino backgrounds are properly included. Flavor evolution of the neutrino background is dominantly smooth. However, in a certain parameter region, coherent undamped oscillations of the neutrino background are possible. In addition, neutrino CP asymmetry is found to be considerably smaller than expected. Reasons are provided for the above effects and some physical implications are discussed.

A record measurement of the proton's magnetism has been achieved by confining a single proton in a device called a double Penning trap. The result opens the way to exploring one of nature's fundamental symmetries. See Letter p.596 Although less prominent than large synchrotron experiments, measurements of fundamental constants or atomic properties can still make valuable contributions to the search of physical laws beyond the Standard Model — if the measurement precision is high enough. In a direct measurement, Andreas Mooser et al. determine the magnetic moment of the proton with unprecedented precision. The measurement is performed using a double Penning trap, a system in which a single ion is confined and manipulated in a powerful homogeneous magnetic field. In combination with a direct measurement of the antiproton magnetic moment, this work will pave the way for a rigorous test of matter–antimatter symmetry.

Classical point-particle relativistic lagrangians are constructed that generate the momentum-velocity and dispersion relations for quantum wave packets in Lorentz-violating effective field theory., Comment: 6 pages, accepted for publication in Physics Letters B

Taken at face value, experimental central values of the masses of the electron and muon neutrinos suggest that they are faster-than-light particles. We summarize the current experimental situation and propose a class of null experiments to settle this issue. We also comment on some theoretical aspects.

The behavior of photons in the presence of Lorentz and CPT violation is studied. Allowing for operators of arbitrary mass dimension, we classify all gauge-invariant Lorentz- and CPT-violating terms in the quadratic Lagrange density associated with the effective photon propagator. The covariant dispersion relation is obtained, and conditions for birefringence are discussed. We provide a complete characterization of the coefficients for Lorentz violation for all mass dimensions via a decomposition using spin-weighted spherical harmonics. The resulting nine independent sets of spherical coefficients control birefringence, dispersion, and anisotropy. We discuss the restriction of the general theory to various special models, including among others the minimal Standard-Model Extension, the isotropic limit, the case of vacuum propagation, the nonbirefringent limit, and the vacuum-orthogonal model. The transformation of the spherical coefficients for Lorentz violation between the laboratory frame and the standard Sun-centered frame is provided. We apply the results to various astrophysical observations and laboratory experiments. Astrophysical searches of relevance include studies of birefringence and of dispersion. We use polarimetric and dispersive data from gamma-ray bursts to set constraints on coefficients for Lorentz violation involving operators of dimensions four through nine, and we describe the mixing of polarizations induced by Lorentz and CPT violation in the cosmic-microwave background. Laboratory searches of interest include cavity experiments. We present the theory for searches with cavities, derive the experiment-dependent factors for coefficients in the vacuum-orthogonal model, and predict the corresponding frequency shift for a circular-cylindrical cavity., 58 pages two-column REVTeX, accepted in Physical Review D

We investigate the implications for experiment of the existence of compactified dimensions with a scale much larger than the Planck length. Such manifolds might occur in certain string models, for instance, if the compactification process is related to the mechanism generating electroweak or supersymmetry breaking. Model-independent upper bounds on the size of any extra dimensions are obtained by examining a wide range of experimental data.

We define the string space-time symmetries C,P,T and their products. The effects of nonlocal interactions and the infinite number of particle fields are incorporated using string field theory. At the dynamical level, C,P,T and their products are preserved by the open bosonic string. Only the product CPT is dynamically preserved by the superstring, although a modified action can be constructed to preserve C. We show that these discrete symmetries may be spontaneously broken in a natural way by string interactions. In a favorable scenario, this might lead to CPT violation in the K-K system just below the limits of present experiments.

Exceptional sensitivity to spacetime torsion can be achieved by searching for its couplings to fermions. Recent experimental searches for Lorentz violation are exploited to extract new constraints involving 19 of the 24 independent torsion components down to levels of order ${10}^{\ensuremath{-}31}\text{ }\text{ }\mathrm{GeV}$.

In the context of covariant string field theory, we investigate the existence and properties of nonperturbative vacua for the open bosonic string. The study is performed using successive orders in a level-truncation method. We find a candidate nonperturbative vacuum and obtain numerical values for nonzero expectation values of all fields to level two. Perturbation theory about this vacuum is shown to be well defined. The occurence and location of poles in the propagators of all fields to level two are established. We observe that string theories necessarily have running couplings at tree level and that the open bosonic string is asymptotically free. The nontrivial momentum dependence means that certain poles seen in the canonical vacuum are absent in the nonperturbative vacuum. This result follows from the nature of the string as an extended object and is likely to hold for general string theories.

Theories with spontaneous local Lorentz and diffeomorphism violation contain massless Nambu-Goldstone modes, which arise as field excitations in the minimum of the symmetry-breaking potential. If the shape of the potential also allows excitations above the minimum, then an alternative gravitational Higgs mechanism can occur in which massive modes involving the metric appear. The origin and basic properties of the massive modes are addressed in the general context involving an arbitrary tensor vacuum value. Special attention is given to the case of bumblebee models, which are gravitationally coupled vector theories with spontaneous local Lorentz and diffeomorphism violation. Mode expansions are presented in both local and spacetime frames, revealing the Nambu-Goldstone and massive modes via decomposition of the metric and bumblebee fields, and the associated symmetry properties and gauge fixing are discussed. The class of bumblebee models with kinetic terms of the Maxwell form is used as a focus for more detailed study. The nature of the associated conservation laws and the interpretation as a candidate alternative to Einstein-Maxwell theory are investigated. Explicit examples involving smooth and Lagrange-multiplier potentials are studied to illustrate features of the massive modes, including their origin, nature, dispersion laws, and effects on gravitational interactions. In the weak static limit, the massive mode and Lagrange-multiplier fields are found to modify the Newton and Coulomb potentials. The nature and implications of these modifications are examined., Comment: 27 pages two-column REVTeX, accepted in Physical Review D

A model of neutrino oscillations is presented that has only three degrees of freedom and is consistent with existing data. The model is a subset of the renormalizable sector of the Standard-Model Extension (SME), and it offers an alternative to the standard three-neutrino massive model. All classes of neutrino data are described, including solar, reactor, atmospheric, and LSND oscillations. The disappearance of solar neutrinos is obtained without matter-enhanced oscillations. Quantitative predictions are offered for the ongoing MiniBooNE experiment and for the future experiments OscSNS, NOvA, and T2K., Comment: 12 pages REVTeX

We find that the use of a general theoretical framework incorporating CPT and Lorentz breaking permits a detailed investigation of possible experimental signatures in Penning-trap experiments. Our results indicate that the sharpest tests of CPT symmetry emerge from comparisons of anomaly frequencies in g — 2 experiments. Our estimates of appropriate figures of merit provide bounds of approximately 1020 in electron-positron experiments and of 1023 for a plausible proton-antiproton experiment, Other signals involving possible diurnal variations provide additional bounds at the level of 1018 in the electron-positron system and 1021 in the proton-antiproton system. A table showing all our estimated bounds is presented in Ref. [10].

The pure-gravity sector of the minimal Standard-Model Extension is studied in the limit of Riemann spacetime. A method is developed to extract the modified Einstein field equations in the limit of small metric fluctuations about the Minkowski vacuum, while allowing for the dynamics of the 20 independent coefficients for Lorentz violation. The linearized effective equations are solved to obtain the post-newtonian metric. The corresponding post-newtonian behavior of a perfect fluid is studied and applied to the gravitating many-body system. Illustrative examples of the methodology are provided using bumblebee models. The implications of the general theoretical results are studied for a variety of existing and proposed gravitational experiments, including lunar and satellite laser ranging, laboratory experiments with gravimeters and torsion pendula, measurements of the spin precession of orbiting gyroscopes, timing studies of signals from binary pulsars, and the classic tests involving the perihelion precession and the time delay of light. For each type of experiment considered, estimates of the attainable sensitivities are provided. Numerous effects of local Lorentz violation can be studied in existing or near-future experiments at sensitivities ranging from parts in 10^4 down to parts in 10^{15}., Comment: 46 pages two-column REVTeX, accepted in Physical Review D

In summary, we find that by using a general framework we are able to analyze proposed tests of CPT in hydrogen and antihydrogen. We find that in addition to testing CPT, these experiments will also test Lorentz symmetry. Our analysis shows that in comparisons of 1S–2S transitions in hydrogen and antihydrogen, control of the spin mixing at the 1S and 2S levels is an essential feature in designing an effective test of CPT and Lorentz symmetry. We also find that high-resolution radio frequency experiments in hydrogen or antihydrogen offer the possibility of new and precise tests of CPT and Lorentz symmetry. One very recent experiment using a double-resonance technique in a hydrogen maser has obtained a new CPT and Lorentz bound at the level of 10−27 for electrons and protons.

In general relativity, gravitational waves propagate at the speed of light, and so gravitons are massless. The masslessness can be traced to symmetry under diffeomorphisms. However, another elegant possibility exists: masslessness can instead arise from spontaneous violation of local Lorentz invariance. We construct the corresponding theory of gravity. It reproduces the Einstein-Hilbert action of general relativity at low energies and temperatures. Detectable signals occur for sensitive experiments, and potentially profound implications emerge for our theoretical understanding of gravity., Comment: 6 pages, accepted in General Relativity and Gravitation

Space-based experiments offer sensitivity to numerous unmeasured effects involving Lorentz and CPT violation. We provide a classification of clock sensitivities and present explicit expressions for time variations arising in such experiments from nonzero coefficients in the Lorentz- and CPT-violating Standard-Model Extension., Comment: 15 pages

An investigation is performed of the Lorentz-violating electrodynamics extracted from the renormalizable sector of the general Lorentz- and CPT-violating standard-model extension. Among the unconventional properties of radiation arising from Lorentz violation is birefringence of the vacuum. Limits on the dispersion of light produced by galactic and extragalactic objects provide bounds of 3 x 10^{-16} on certain coefficients for Lorentz violation in the photon sector. The comparative spectral polarimetry of light from cosmologically distant sources yields stringent constraints of 2 x 10^{-32}. All remaining coefficients in the photon sector are measurable in high-sensitivity tests involving cavity-stabilized oscillators. Experimental configurations in Earth- and space-based laboratories are considered that involve optical or microwave cavities and that could be implemented using existing technology., 23 pages REVTeX

Spacetime-varying coupling constants can be associated with violations of local Lorentz invariance and CPT symmetry. An analytical supergravity cosmology with time-varying fine-structure constant provides an explicit example. Estimates are made for some experimental constraints., Comment: 4 pages