Lorentz Invariance Violation Research Articles

New constraints on Lorentz Invariance violation from Crab Nebula spectrum beyond 100\xa0TeV

Recently two collaborations, Tibet and HAWC, presented new measurements of gamma-ray spectrum from Crab Nebula (Amenomori et al. in Phys Rev Lett 123(5):051101, 2019, arXiv:1906.05521 [astro-ph.HE]; Abeysekara et al. [HAWC Collaboration] in Astrophys. J. 881, 134, (2019), arXiv:1905.12518 [astro-ph.HE]) which continues beyond 100 TeV. We use these data to establish two-sided constraints on parameters of Lorentz Invariance violation in quantum electrodynamics. The limits on Lorentz violating mass scale for quartic dispersion relation are 4.1times 10^{14}, text{ GeV } (photon splitting) and 1.9times 10^{13}, text{ GeV } (photon decay) for superluminal case, and 1.4times 10^{12} GeV (suppression of shower formation) for subluminal case.

Optimal estimation of parameters for scalar field in an expanding spacetime exhibiting Lorentz invariance violation

We address the optimal estimation of quantum parameters, in the framework of local quantum estimation theory, for a massive scalar quantum field in the expanding Robertson–Walker universe exhibiting Lorentz invariance violation (LIV). We find that, in the estimation of cosmological parameters, the ultimate bounds to the precision of the Lorentz-invariant massive scalar field can be improved due to the effects of LIV under some appropriate conditions. We also show that, in the Lorentz-invariant massive scalar field and massless scalar field due to LIV backgrounds, the optimal precision can be achieved by choosing the particles with some suitable LIV, cosmological and field parameters. Moreover, in the estimation of LIV parameter during the spacetime expansion, we prove that the appropriate momentum mode of field particles and larger cosmological parameters can provide us a better precision.

Long-term stable optical cavity for special relativity tests in space.

BOOST (BOOst Symmetry Test) is a proposed space mission to search for Lorentz invariance violations and aims to improve the Kennedy-Thorndike parameter constraint by two orders of magnitude. The mission consists of comparing two optical frequency references of different nature, an optical cavity and a hyperfine transition in molecular iodine, in a low Earth orbit. Naturally, the stability of the frequency references at the orbit period of 5400 s (f=0.18 mHz) is essential for the mission success. Here we present our experimental efforts to achieve the required fractional frequency stability of 7.4×10-14 Hz -1/2 at 0.18 mHz (in units of the square root of the power spectral density), using a high-finesse optical cavity. We have demonstrated a frequency stability of (9±3)×10-14 Hz -1/2 at 0.18 mHz, which corresponds to an Allan deviation of 10-14 at 5400 s. A thorough noise source breakdown is presented, which allows us to identify the critical aspects to consider for a future space-qualified optical cavity for BOOST. The major noise contributor at sub-milli-Hertz frequency was related to intensity fluctuations, followed by thermal noise and beam pointing. Other noise sources had a negligible effect on the frequency stability, including temperature fluctuations, which were strongly attenuated by a five-layer thermal shield.

Lorentz Violation Footprints in the Spectrum of High-Energy Cosmic Neutrinos—Deformation of the Spectrum of Superluminal Neutrinos from Electron-Positron Pair Production in Vacuum

The observation of cosmic neutrinos up to 2 PeV is used to put bounds on the energy scale of Lorentz invariance violation through the loss of energy due to the production of e + e - pairs in the propagation of superluminal neutrinos. A model to study this effect, which allows us to understand qualitatively the results of numerical simulations, is presented.

Constraints on neutrino speed, weak equivalence principle violation, Lorentz invariance violation, and dual lensing from the first high-energy astrophysical neutrino source TXS 0506+056

We derive stringent constraints on neutrino speed, weak equivalence principle violation, Lorentz invariance violation, and dual lensing from the first high-energy astrophysical neutrino source: TXS 0506+056. Observation of neutrino (IceCube-170922A) and photons in a similar time frame and from the same direction is used to derive these limits. We describe ways in which these constraints can be further improved by orders of magnitude.

Consistency analysis of a CPT-even and CPT-odd Lorentz-violating effective field theory in the electrodynamics at Planck scale by an influence of a background isotropic field

Based on the motivation that some quantum gravity theories predicts the Lorentz Invariance Violation (LIV) around Planck-scale energy levels, this paper proposes a new formalism that addresses the possible effects of LIV in electrodynamics. This formalism is capable of changing the usual electrodynamics through high derivative arbitrary mass dimension terms that includes a constant background field controlling the intensity of LIV in the models, producing modifications in the dispersion relations in a manner that is similar to the Myers–Pospelov approach. With this framework, it was possible to generate a CPT-even and CPT-odd generalized modifications of the electrodynamics in order to study the stability and causality of these theories considering the isotropic case for the background field. An additional analysis of unitarity at tree level was considered by studying the saturated propagators. After this analysis, we conclude that, while CPT-even modifications always preserve the stability, causality and unitarity in the boundaries of the effective field theory and therefore may be good candidates for field theories with interactions, the CPT-odd one violates causality and unitarity. This feature is a consequence of the vacuum birefringence characteristics that are present in CPT-odd theories for the photon sector.

Modifications to Plane Gravitational Waves from Minimal Lorentz Violation

General Relativity predicts two modes for plane gravitational waves. When a tiny violation of Lorentz invariance occurs, the two gravitational wave modes are modified. We use perturbation theory to study the detailed form of the modifications to the two gravitational wave modes from the minimal Lorentz-violation coupling. The perturbation solution for the metric fluctuation up to the first order in Lorentz violation is discussed. Then, we investigate the motions of test particles under the influence of the plane gravitational waves with Lorentz violation. First-order deviations from the usual motions are found.

Homogeneously Modified Special relativity (HMSR)

This work explores a Standard Model extension possibility, that violates Lorentz invariance, preserving the space-time isotropy and homogeneity. In this sense HMSR represents an attempt to introduce an isotropic Lorentz Invariance Violation in the elementary particle SM. The theory is constructed starting from a modified kinematics, that takes into account supposed quantum effects due to interaction with the space-time background. The space-time structure itself is modified, resulting in a pseudo-Finsler manifold. The SM extension here provided is inspired by the effective fields theories, but it preserves covariance, with respect to newly introduced modified Lorentz transformations. Geometry perturbations are not considered as universal, but particle species dependent. Non universal character of the amended Lorentz transformations allows to obtain visible physical effects, detectable in experiments by comparing different perturbations related to different interacting particles species.

About the Measure of the Bare Cosmological Constant

I try to revive, and possibly reconcile, a debate started a few years ago, about the relative roles of a bare cosmological constant and of a vacuum energy, by taking the attitude to try to get the most from the physics now available as established. I notice that the bare cosmological constant of the Einstein equations, which is there ever since GR emerged, is actually constrained (if not measured) indirectly combining the effective cosmological constant observed now, as given by ΛCDM Precision Cosmology, with the cumulative vacuum contribution of the particles of the Standard Model, SM. This comes out when the vacuum energy is regularized, as given by many Authors, still within well established Quantum Field Theory, QFT, but without violating Lorentz invariance. The fine tuning, implied by the compensation to a small positive value of the two large contributions, could be seen as offered by Nature, which provides one more fundamental constant, the bare Lambda. The possibility is then discussed of constraining (measuring) directly such a bare cosmological constant by the features of primordial gravitational wave signals coming from epoch’s precedent to the creation of particles. I comment on possibilities that would be lethal, that is if the vacuum does not gravitate. This last issue is often raised, and I discuss the current situation about. Finally a hint is briefly discussed for a possible “bare Lambda inflation” process.

Probing of violation of Lorentz invariance by ultracold neutrons in the Standard Model Extension

We analyze a dynamics of ultracold neutrons (UCNs) caused by interactions violating Lorentz invariance within the Standard Model Extension (SME) (Colladay and Kostelecký (1997) [3] and Kostelecký (2004) [1]). We use the effective non–relativistic potential for interactions violating Lorentz invariance derived by Kostelecký and Lane (1999) [47] and calculate contributions of these interactions to the transition frequencies of transitions between quantum gravitational states of UCNs bouncing in the gravitational field of the Earth. Using the experimental sensitivity of qBounce experiments we make some estimates of upper bounds of parameters of Lorentz invariance violation in the neutron sector of the SME which can serve as a theoretical basis for an experimental analysis. We show that an experimental analysis of transition frequencies of transitions between quantum gravitational states of unpolarized and polarized UCNs should allow to place some new constraints in comparison to the results adduced by Kostelecký and Russell (2011) [16].

Future CMB constraints on cosmic birefringence and implications for fundamental physics

The primary scientific target of the ground- and space-based cosmic microwave background (CMB) polarization experiments currently being built and proposed is the detection of primordial tensor perturbations. As a byproduct, these instruments will significantly improve constraints on cosmic birefringence, or the rotation of the CMB polarization plane. If convincingly detected, cosmic birefringence would be a dramatic manifestation of physics beyond the standard models of particle physics and cosmology. We forecast the bounds on the cosmic polarization rotation (CPR) from the upcoming ground-based Simons Observatory (SO) and the space-based LiteBIRD experiments, as well as a ``fourth-generation'' ground-based CMB experiment like CMB-S4 and the midcost space mission PICO. We examine the detectability of both a stochastic anisotropic rotation field, as well as an isotropic rotation by a constant angle. CPR induces new correlations of CMB observables, including spectra of parity-odd type in the case of isotropic CPR, and mode-coupling correlations in the anisotropic rotation case. We find that LiteBIRD and SO will reduce the $1\ensuremath{\sigma}$ bound on the isotropic CPR from the current value of 30 arcmin to 1.5 and 0.6 arcmin, respectively, while a CMB-S4-like experiment and PICO will reduce it to $\ensuremath{\sim}0.1\text{ }\text{ }\mathrm{arcmin}$. The bounds on the amplitude of a scale-invariant CPR spectrum will be reduced by 1, 2, and 3 orders of magnitude by LiteBIRD, SO, and CMB-S4-like/PICO, respectively. We discuss potential implications for fundamental physics by interpreting the forecasted bounds on CPR in terms of the corresponding constraints on pseudoscalar fields coupled to electromagnetism, primordial magnetic fields (PMF), and violations of Lorentz invariance. We find that CMB-S4-like and PICO can reduce the $1\ensuremath{\sigma}$ bound on the amplitude of the scale-invariant PMF from 1 to 0.1 nG, while also probing the magnetic field of the Milky Way. The upcoming experiments will also tighten bounds on the axion-photon coupling, with SO improving the bound from ${f}_{a}\ensuremath{\gtrsim}50{H}_{I}$ at present, where ${H}_{I}$ is the energy scale of inflation, to ${f}_{a}\ensuremath{\gtrsim}500{H}_{I}$, and CMB-S4-like and PICO raising it to ${f}_{a}\ensuremath{\gtrsim}\mathrm{few}\ifmmode\times\else\texttimes\fi{}{10}^{3}{H}_{I}$, placing stringent constraints on the string theory axions.

Constraints on the emission region of 3C 279 during strong flares in 2014 and 2015 through VHE γ-ray observations with H.E.S.S.

The flat spectrum radio quasar 3C 279 is known to exhibit pronounced variability in the high-energy (100 MeV < E < 100 GeV) γ-ray band, which is continuously monitored with Fermi-LAT. During two periods of high activity in April 2014 and June 2015 target-of-opportunity observations were undertaken with the High Energy Stereoscopic System (H.E.S.S.) in the very-high-energy (VHE, E > 100 GeV) γ-ray domain. While the observation in 2014 provides an upper limit, the observation in 2015 results in a signal with 8.7σ significance above an energy threshold of 66 GeV. No VHE variability was detected during the 2015 observations. The VHE photon spectrum is soft and described by a power-law index of 4.2 ± 0.3. The H.E.S.S. data along with a detailed and contemporaneous multiwavelength data set provide constraints on the physical parameters of the emission region. The minimum distance of the emission region from the central black hole was estimated using two plausible geometries of the broad-line region and three potential intrinsic spectra. The emission region is confidently placed at r ≳ 1.7 × 1017 cm from the black hole, that is beyond the assumed distance of the broad-line region. Time-dependent leptonic and lepto-hadronic one-zone models were used to describe the evolution of the 2015 flare. Neither model can fully reproduce the observations, despite testing various parameter sets. Furthermore, the H.E.S.S. data were used to derive constraints on Lorentz invariance violation given the large redshift of 3C 279.

Lorentz violation and quantum mechanics

We report and discuss the results of double-slit-like experiments in the infrared range, which evidence an anomalous behaviour of photon systems under particular (energy and space) constraints. These outcomes apparently disagree both with standard quantum mechanics (Copenhagen interpretation) and with classical and quantum electrodynamics. Possible interpretations can be given in terms of either the existence of de Broglie–Bohm pilot waves associated to photons, and/or the violation of local Lorentz invariance (LLI). We put forward an intriguing hypothesis about the possible connection between these seemingly unrelated points of view by assuming that the pilot wave of a photon is, in the framework of LLI violation, a local deformation of the flat Minkowski spacetime.

Detailed studies of ^{100}Mo two-neutrino double beta decay in NEMO-3

The full data set of the NEMO-3 experiment has been used to measure the half-life of the two-neutrino double beta decay of ^{100}Mo to the ground state of ^{100}Ru, T_{1/2} = left[ 6.81 pm 0.01,left( text{ stat }right) ^{+0.38}_{-0.40},left( text{ syst }right) right] times 10^{18} year. The two-electron energy sum, single electron energy spectra and distribution of the angle between the electrons are presented with an unprecedented statistics of 5times 10^5 events and a signal-to-background ratio of sim 80. Clear evidence for the Single State Dominance model is found for this nuclear transition. Limits on Majoron emitting neutrinoless double beta decay modes with spectral indices of mathrm{n}=2,3,7, as well as constraints on Lorentz invariance violation and on the bosonic neutrino contribution to the two-neutrino double beta decay mode are obtained.

Relativistic dispersion relation and putative metric structure in noncommutative phase-space

The deformation of the relativistic dispersion relation caused by noncommutative (NC) Quantum Mechanics (QM) is studied using the extended phase-space formalism. The introduction of the additional commutation relations induces Lorentz invariance violation. It is shown that this deformation does not affect the propagation speed of free massless particles. From the deformation of the dispersion relation for massless particles, gamma ray burst data is used to establish an upper bound on the noncommutative parameter, η, namely η≲10−12eV/c. Additionally, a putative metric structure for the noncommutative phase-space is discussed.

Neutrino recoil force in electron-capture decay of polarized nuclei: Measurement prospects and potential applications

Due to a directional asymmetry of neutrino emission caused by parity violation, a sample of radioactive atoms experiences a small recoil force from neutrino radiation accompanying electron capture by polarized nuclei. An expression for this force is obtained for the case of allowed nuclear transitions. Prospects to measure this force by the use of modern micromechanical devices are considered. Numerical estimates for the force are presented for a number of most suitable radioactive isotopes. Potential applications for the weak interaction studies are discussed including the possibility to search for hypothetical Lorentz invariance violation.

Robust constraint on Lorentz violation using Fermi-LAT gamma-ray burst data

Models of quantum gravity suggest that the vacuum should be regarded as a medium with quantum structure that may have non-trivial effects on photon propagation, including the violation of Lorentz invariance. Fermi Large Area Telescope (LAT) observations of gamma-ray bursts (GRBs) are sensitive probes of Lorentz invariance, via studies of energy-dependent timing shifts in their rapidly-varying photon emissions. In this paper we analyze the Fermi-LAT measurements of high-energy gamma rays from GRBs with known redshifts, allowing for the possibility of energy-dependent variations in emission times at the sources as well as a possible non-trivial refractive index in vacuo for photons. We use statistical estimators based on the irregularity, kurtosis and skewness of bursts that are relatively bright in the 100 MeV to multi-GeV energy band to constrain possible dispersion effects during propagation. We find that the energy scale characterizing a linear energy dependence of the refractive index should exceed a few $\times 10^{17}$ GeV, and we estimate the sensitivity attainable with additional future sources to be detected by Fermi-LAT.

An experimental test of gravity at high energy

Gravitational lensing of very high energy photons has recently been observed in the JVAS B0218+357 strong lensing system. This observation opens the possibility of performing a test of gravity at high energy by comparing the difference in propagation time of high energy photons over different travel paths. The time delay is computed in the framework of a LIV (Lorentz Invariance Violation) extension of the equations of motion of photons in the field of a massive object. However, the method obtained can be transposed to other models of gravity at high energy. The potential for constraining high energy gravity with future observations of JVAS B0218+357 is discussed. The bounds on the LIV energy scale will not be competitive with other astrophysical bounds such as those coming from AGN and GRB flares. However, these bounds are free of any assumption on the emission process.

Photon splitting constraint on Lorentz invariance violation from Crab Nebula spectrum

We calculate the decay width of the photon splitting into three photons in a model of quantum electrodynamics with broken Lorentz invariance. We show that this process can lead to a cut-off in the very-high-energy part of a photon spectra of astrophysical sources. We obtain the 95% CL bound on the Lorentz violating mass scale for photons from the analysis of the very-high-energy part of the Crab Nebula spectrum, obtained by HEGRA. This bound improves previous constraints by more than an order of magnitude.

"Radiation Damping" in gas spin comagnetometers.

We report a new kind of interaction between overlapping Rb-Xe spin ensembles polarized by spin-exchange optical pumping. The Rb acts as both a medium to optically polarize the Xe spins and as a magnetometer to probe the precession of Xe spins. When Xe spins precess, they result in the precession of Rb spins. Like the radiation damping effect caused by the coil in conventional NMR systems, the precessing Rb spins lead to damping and a frequency-shift for the precessing Xe spins. When Xe spins are operated in a free-induction decay mode, the transverse relaxation time and oscillating frequency of Xe spins change due to the "radiation damping" effect of Rb spins. When Xe spins are operated in the self-oscillating mode, its transverse relaxation time and oscillating frequency will also be changed. These effects will influence the accuracy of NMR probes, which are widely used in the search for CPT- and Lorentz-invariance violations, the fifth force, etc. If this problem is solved or compensated for, the limit of the aforementioned search may be improved.