arXiv subjects

Brett Altschul

Publications and source records attributed to Brett Altschul.

62 records · Page 4Linked to original sources

arXiv2007

Astrophysical Bounds on the Photon Charge and Magnetic Moment

If the photon possessed an electric charge or a magnetic moment, light waves propagating through magnetic fields would acquire new quantum mechanical phases. For a charged photon, this is an Aharonov-Bohm phase, and the fact that we can resolve distant galaxies using radio interferometry indicates that this phase must be small. This in turn constrains the photon charge to be smaller that 10^(-32) e if all photons have the same charge and smaller than 10^(-46) e if there are both positively and negatively charged photons. The best bound on the magnetic moment comes from the observed absence of wavelength-independent photon birefringence. Birefringence measurements, which compare the relative phases of right- and left-circularly polarized waves, restrict the magnetic moment to be less than 10^(-24) e cm. This is just a few orders of magnetude weaker than the experimental bounds on the electron and neutron electric dipole moments.

hep-th↗

arXiv2007

Finite Duration and Energy Effects in Lorentz-Violating Vacuum Cerenkov Radiation

Vacuum Cerenkov radiation is possible in certain Lorentz-violating quantum field theories, when very energetic charges move faster than the phase speed of light. In the presence of a CPT-even, Lorentz-violating modification of the photon sector, the character of the Cerenkov process is controlled by the high-frequency behavior of the radiation spectrum. The development of the Cerenkov process can be markedly different, depending on whether the only limits on the emission of very energetic photons come from energy-momentum conservation or whether there are additional effects that cut off the spectrum at high frequencies. Moreover, since the high-frequency cutoff determines the total rate at which an emitting charge loses energy, it also controls all aspects of the emission that are related to the process's finite duration.

hep-th↗

arXiv2007

Bound on the Photon Charge from the Phase Coherence of Extragalactic Radiation

If the photon possessed a nonzero charge, then electromagnetic waves traveling along different paths would acquire Aharonov-Bohm phase differences. The fact that such an effect has not hindered interferometric astronomy places a bound on the photon charge estimated to be at the 10^(-32) e level if all photons have the same charge and 10^(-46) e if different photons can carry different charges.

hep-ph↗

arXiv2007

Cerenkov Radiation in a Lorentz-Violating and Birefringent Vacuum

We calculate the emission spectrum for vacuum Cerenkov radiation in Lorentz-violating extensions of electrodynamics. We develop an approach that works equally well if the presence or the absence of birefringence. In addition to confirming earlier work, we present the first calculation relevant to Cerenkov radiation in the presence of a birefringent photon k_F term, calculating the lower-energy part of the spectrum for that case.

hep-th↗

arXiv2006

Bounds on Spin-Dependent Lorentz Violation From Inverse Compton Observations

Some of the best bounds on possible Lorentz violation in the electron sector come from observations of high-energy astrophysical phenomena. Using measurements of TeV inverse Compton radiation from a number of sources, we place the first bounds--at the 10^(-15) level--on seven of the electron d coefficients.

hep-ph↗

arXiv2006

Astrophysical Limits on Lorentz Violation for All Charged Species

If Lorentz violation exists, it will affect the thresholds for pair creation processes. Lorentz-violating operators that change the maximum velocities of charged particles may increase or decrease the extinction rate of gamma-rays moving through space. If the emissions from high-energy astrophysical sources do not show any signs of anomalous absorption, this allows us to place bounds on the Lorentz-violating c coefficients for multiple species of charged particles. The bounds for a species of mass m_X based on observing photons at an energy E can be O(m_X^2/E^2), which corresponds to limits at the 10^(-15)(m_X^2/m_e^2) level for the most energetic photons.

hep-ph↗

arXiv2006

Vacuum Cerenkov Radiation in Lorentz-Violating Theories Without CPT Violation

In theories with broken Lorentz symmetry, Cerenkov radiation may be possible even in vacuum. We analyze the Cerenkov emissions that are associated with the least constrained Lorentz-violating modifications of the photon sector, calculating the threshold energy, the frequency spectrum, and the shape of the Mach cone. In order to obtain sensible results for the total power emitted, we must make use of information contained within the theory which indicates at what scale new physics must enter.

hep-th↗

arXiv2006

Synchrotron and Inverse Compton Constraints on Lorentz Violations for Electrons

We present a method for constraining Lorentz violation in the electron sector, based on observations of the photons emitted by high-energy astrophysical sources. The most important Lorentz-violating operators at the relevant energies are parameterized by a tensor c^{nu mu) with nine independent components. If c is nonvanishing, then there may be either a maximum electron velocity less than the speed of light or a maximum energy for subluminal electrons; both these quantities will generally depend on the direction of an electron's motion. From synchrotron radiation, we may infer a lower bound on the maximum velocity, and from inverse Compton emission, a lower bound on the maximum subluminal energy. With observational data for both these types of emission from multiple celestial sources, we may then place bounds on all nine of the coefficients that make up c. The most stringent bound, on a certain combination of the coefficients, is at the 6 x 10^(-20) level, and bounds on the coefficients individually range from the 7 x 10^(-15) level to the 2 x 10^(-17) level. For most of the coefficients, these are the most precise bounds available, and with newly available data, we can already improve over previous bounds obtained by the same methods.

hep-ph↗