arXiv subjects

Brett Altschul

Publications and source records attributed to Brett Altschul.

At least 55 records · Page 3Linked to original sources

arXiv2013

Lorentz and CPT Violation in Scalar-Mediated Potentials

In Lorentz- and CPT-violating effective field theories involving scalar and spinor fields, there exist forms of Lorentz violation that modify only the scalar-spinor Yukawa interaction vertices. These affect low-energy fermion and antifermion scattering processes through modifications to the nonrelativistic Yukawa potentials. The modified potentials involve novel combinations of momentum, spin, and Lorentz-violating background tensors.

hep-th↗

arXiv2012

Coupling Right- and Left-Handed Photons Differently to Charged Matter

We consider a modification of electrodynamics in which right- and left-circularly polarized photons are coupled to charged sources differently. Even though photon helicity is a Lorentz invariant quantity, such a modification breaks Lorentz symmetry, as well as locality. The modified theory includes novel magnetic forces between perpendicular currents. Existing data can be used to constrain the modification at approximately a 2 x 10^(-3) level.

hep-th↗

arXiv2012

Quantum Effects of a Spacetime Varying alpha on the Propagation of Electrically Charged Fermions

A spacetime-varying fine structure constant alpha(x^mu) could generate quantum corrections in some of the coefficients of the Lorentz-violating standard model extension (SME) associated with electrically charged fermions. The quantum corrections depend on d_mu alpha, the spacetime gradient of the fine structure constant. Lorentz-violating operators involving fermions arise from the one-loop corrections to the quantum electrodynamics (QED) vertex function and fermion self-energy. Both g^(lambda mu nu) and c^(mu nu) terms are generated, at O(d_mu alpha) and O[(d_mu alpha)^2], respectively. The g^(lambda mu nu) terms so generated are different in the vertex and self-energy, which represents a radiatively induced violation of gauge invariance.

hep-ph↗

arXiv2011

Consequences of Neutrino Lorentz Violation For Leptonic Meson Decays

If the observation by OPERA of apparently superluminal neutrinos is correct, the Lagrangian for second-generation leptons must break Lorentz invariance. We calculate the effects of an energy-independent change in the neutrino speed on another observable, the charged pion decay rate. The rate decreases by an factor [1 - 3/(1 - (m_mu)^2 / (m_pi) ^ 2) (< v_(nu) > - 1)], where < v_(nu) > is the (directionally averaged) neutrino speed in the pion's rest frame. This provides a completely independent experimental observable that is sensitive to the same forms of Lorentz violation as a neutrino time of flight measurement.

hep-ph↗

arXiv2011

Bounding Lorentz Violation at Particle Colliders By Tracking the Motion of Charged Particles

In the presence of Lorentz violation, the motion of a charged particle in a magnetic field is distorted. By measuring the eccentricities of particles' elliptical orbits and studying how those eccentricities vary with the absolute orientation of the laboratory, it is possible to constrain the Lorentz-violating c_JK parameters. For each observed species, this method can provide constraints on four linear combinations of coefficients for which, in some species, there are presently no two-sided bounds.

hep-ph↗

arXiv2011

Renormalization of Scalar and Yukawa Field Theories with Lorentz Violation

We consider a theory of scalar and spinor fields, interacting through Yukawa and phi^4 interactions, with Lorentz-violating operators included in the Lagrangian. We compute the leading quantum corrections in this theory. The renormalizability of the theory is explicitly shown up to one-loop order. In the pure scalar sector, the calculations can be generalized to higher orders and to include finite terms, because the theory can be solved in terms of its Lorentz-invariant version.

hep-th↗

arXiv2011

Modeling-Free Bounds on Nonrenormalizable Isotropic Lorentz and CPT Violation in QED

The strongest bounds on some forms of Lorentz and CPT violation come from astrophysical data, and placing such bounds may require understanding and modeling distant sources of radiation. However, it is also desirable to have bounds that do not rely on these kinds of detailed models. Bounds that do not rely on any modeling of astrophysical objects may be derived both from laboratory experiments and certain kinds of astrophysical observations. The strongest such bounds on isotropic modifications of electron, positron, and photon dispersion relations of the form E^2 = p^2 + m^ 2 + epsilon p^3 come from data on cosmological birefringence, the absence of photon decay, and radiation from lepton beams. The bounds range in strength from the 4 x 10^(-13) to 6 x 10^(-33) (GeV)^(-1) levels.

hep-ph↗

arXiv2011

Limits on the Time Variation of the Fermi Constant G_F Based on Type Ia Supernova Observations

The light curve of a type Ia supernova decays at a rate set by the beta-decay lifetimes of the Ni-56 and Co-56 produced in the explosion. This makes such a light curve sensitive to the value of the Fermi constant G_F at the time of the supernova. Using data from the CfA Supernova Archive, we measure the dependence of the light curve decay rate on redshift and place a bound on the time variation of G_F of |(dG_F/dt)/G_F| < 10^(-9) / y.

hep-ph↗

arXiv2010

Testing Photons' Bose-Einstein Statistics With Compton Scattering

It is an empirical question whether photons always obey Bose-Einstein statistics, but devising and interpreting experimental tests of photon statistics can be a challenge. The nonrelativistic cross section for Compton scattering illustrates how a small admixture nu of wrong-sign statistics leads to a loss of gauge invariance; there is a large anomalous amplitude for scattering timelike photons. Nevertheless, one can interpret the observed transparency of the solar wind plasma at low frequencies as a bound nu < 10^(-25) if Lorentz symmetry is required. If there is instead a universal preferred frame, the bound is nu < 10^(-14), still strong compared with previous results.

hep-ph↗

arXiv2010

Laboratory Bounds on Electron Lorentz Violation

Violations of Lorentz boost symmetry in the electron and photon sectors can be constrained by studying several different high-energy phenomenon. Although they may not lead to the strongest bounds numerically, measurements made in terrestrial laboratories produce the most reliable results. Laboratory bounds can be based on observations of synchrotron radiation, as well as the observed absences of vacuum Cerenkov radiation. Using measurements of synchrotron energy losses at LEP and the survival of TeV photons, we place new bounds on the three electron Lorentz violation coefficients c_(TJ), at the 3 x 10^(-13) to 6 x 10^(-15) levels.

hep-ph↗

arXiv2009

Lorentz violation with an antisymmetric tensor

Field theories with spontaneous Lorentz violation involving an antisymmetric 2-tensor are studied. A general action including nonminimal gravitational couplings is constructed, and features of the Nambu-Goldstone and massive modes are discussed. Minimal models in Minkowski spacetime exhibit dualities with Lorentz-violating vector and scalar theories. The post-newtonian expansion for nonminimal models in Riemann spacetime involves qualitatively new features, including the absence of an isotropic limit. Certain interactions producing stable Lorentz-violating theories in Minkowski spacetime solve the renormalization-group equations in the tadpole approximation.

gr-qc↗

arXiv2009

Testing Electron Boost Invariance with 2S-1S Hydrogen Spectroscopy

There are few good direct laboratory tests of boost invariance for electrons, because the experiments required often involve repeated precision measurements performed at different times of year. However, existing measurements and remeasurements of the 2S-1S two-photon transition frequency in H--which were done to search for a time variation in the fine structure constant--also constitute a measurement of the boost symmetry violation parameter 0.83c_(TX) + 0.51c_(TY) + 0.22c_(TZ) = (4 +/- 8) x 10^(-11). This is an eight order of magnitude improvement over preexisting laboratory bounds, and with only one additional measurements, this system could yield a second comparable constraint.

hep-ph↗

arXiv2009

Bounding Isotropic Lorentz Violation Using Synchrotron Losses at LEP

Some deviations from special relativity--especially isotropic effects--are most efficiently constrained using particles with velocities very close to 1. While there are extremely tight bounds on some of the relevant parameters coming from astrophysical observations, many of these rely on our having an accurate understanding of the dynamics of high-energy sources. It is desirable to have reliable laboratory constraints on these same parameters. The fastest-moving particles in a laboratory were electrons and positrons at LEP. The energetics of the LEP beams were extremely well understood, and measurements of the synchrotron emission rate indicate that that any isotropic deviation of the speed of light from 1 must be smaller than 5 x 10^(-15).

hep-ph↗

arXiv2009

Radiatively Induced Lorentz and Gauge Symmetry Violation in Electrodynamics with Varying alpha

A time-varying fine structure constant alpha(t) could give rise to Lorentz- and CPT-violating changes to the vacuum polarization, which would affect photon propagation. Such changes to the effective action can violate gauge invariance, but they are otherwise permitted. However, in the minimal theory of varying alpha, no such terms are generated at lowest order. At second order, vacuum polarization can generate an instability--a Lorentz-violating analogue of a negative photon mass squared -m^2 proportional to alpha [(d alpha/dt) / alpha]^2 log (Lambda^2), where Lambda is the cutoff for the low-energy effective theory.

hep-th↗

arXiv2009

Disentangling Forms of Lorentz Violation With Complementary Clock Comparison Experiments

Atomic clock comparisons provide some of the most precise tests of Lorentz and CPT symmetries in the laboratory. With data from multiple such experiments using different nuclei, it is possible to constrain new regions of the parameter space for Lorentz violation. Relativistic effects in the nuclei allow us to disentangle forms of Lorentz violation which could not be separately measured in purely nonrelativistic experiments. The disentangled bounds in the neutron sectors are at the 10^(-28) GeV level, far better than could be obtained with any other current technique.

hep-ph↗

arXiv2008

Lorentz Violation and Alpha-Decay

Relating the effective Lorentz violation coefficients for composite particles to the coefficients for their constituent fields is a challenging problem. We calculate the Lorentz violation coefficients relevant to the dynamics of an alpha-particle in terms of proton and neutron coefficients. The alpha-particle coefficients would lead to anisotropies in the alpha-decays of nuclei, and because the decay process involves quantum tunneling, the effects of any Lorentz violations could be exponentially enhanced.

hep-ph↗

arXiv2008

Limits on Neutron Lorentz Violation from the Stability of Primary Cosmic Ray Protons

Recent evidence appears to confirm that the ultra-high-energy primary cosmic ray spectrum consists mostly of protons. The fact that these protons can traverse large distances to reach Earth allows us to place bounds on Lorentz violations. The protons neither emit vacuum Cerenkov radiation nor $β$-decay into neutrons, and this constrains six previously unmeasured coefficients in the neutron sector at the 5 x 10^(-14) level. Among the coefficients bounded here for the first time are those that control spin-independent boost anisotropy for neutrons. This is a phenomenon which could have existed (in light of the preexisting bounds) without additional fine tuning. There are also similar bounds for others species of hadrons. The bounds on Lorentz violation for neutral pions are particularly strong, at the 4 x 10^(-21) level, eleven orders of magnitude better than previous constraints.

hep-ph↗

arXiv2007

Astrophysical Limits on Lorentz Violation for Pions

Pions, like nucleons, are composed primarily of up and down quarks and gluons. Constraints on spin-independent Lorentz violation in the proton, neutron, and pion sectors translate into bounds on Lorentz violation for the fundamental fields. The best bounds on pion Lorentz violation come from astrophysical measurements. The absence of the absorption process gamma --> pi^(+) + pi^(-) for up to 50 TeV photons constrains the possibility that pions' maximum achievable velocities are less than 1 at the 1.5 x 10^(-11) level. The fact that pions with energies up to 30 TeV are observed to decay into photons rather than hadrons bounds the possibility of a maximum velocity greater than 1 at the $2 x 10^(-9) level. This provides the first two-sided bounds on Lorentz violation for pions.

hep-ph↗