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Agullo, I., del Rio, A., & Navarro-Salas, J. (2018). On the Electric-Magnetic Duality Symmetry: Quantum Anomaly, Optical Helicity, and Particle Creation. Symmetry-Basel, 10(12), 763–14pp.
Abstract: It is well known that not every symmetry of a classical field theory is also a symmetry of its quantum version. When this occurs, we speak of quantum anomalies. The existence of anomalies imply that some classical Noether charges are no longer conserved in the quantum theory. In this paper, we discuss a new example for quantum electromagnetic fields propagating in the presence of gravity. We argue that the symmetry under electric-magnetic duality rotations of the source-free Maxwell action is anomalous in curved spacetimes. The classical Noether charge associated with these transformations accounts for the net circular polarization or the optical helicity of the electromagnetic field. Therefore, our results describe the way the spacetime curvature changes the helicity of photons and opens the possibility of extracting information from strong gravitational fields through the observation of the polarization of photons. We also argue that the physical consequences of this anomaly can be understood in terms of the asymmetric quantum creation of photons by the gravitational field.
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Amarilo, K. M., Ferreira Filho, M. B., Araujo Filho, A. A., & Reis, J. A. A. S. (2024). Gravitational waves effects in a Lorentz-violating scenario. Phys. Lett. B, 855, 138785–7pp.
Abstract: This paper focuses on how the production and polarization of gravitational waves are affected by spontaneous Lorentz symmetry breaking, which is driven by a self-interacting vector field. Specifically, we examine the impact of a smooth quadratic potential and a non-minimal coupling, discussing the constraints and causality features of the linearized Einstein equation. To analyze the polarization states of a plane wave, we consider a fixed vacuum expectation value (VEV) of the vector field. Remarkably, we verify that a space-like background vector field modifies the polarization plane and introduces a longitudinal degree of freedom. In order to investigate the Lorentz violation effect on the quadrupole formula, we use the modified Green function. Finally, we show that the space-like component of the background field leads to a third-order time derivative of the quadrupole moment, and the bounds for the Lorentz-breaking coefficients are estimated as well.
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ANTARES and HESS Collaborations(Petroff, E. et al), Barrios-Marti, J., Hernandez-Rey, J. J., Illuminati, G., Lotze, M., Tönnis, C., et al. (2017). A polarized fast radio burst at low Galactic latitude. Mon. Not. Roy. Astron. Soc., 469(4), 4465–4482.
Abstract: We report on the discovery of a new fast radio burst (FRB), FRB 150215, with the Parkes radio telescope on 2015 February 15. The burst was detected in real time with a dispersion measure (DM) of 1105.6 +/- 0.8 pc cm(-3), a pulse duration of 2.8(-0.5)(+1.2) ms, and a measured peak flux density assuming that the burst was at beam centre of 0.7(-0.1)(+0.2) Jy. The FRB originated at a Galactic longitude and latitude of 24.66 degrees, 5.28 degrees and 25 degrees away from the Galactic Center. The burst was found to be 43 +/- 5 per cent linearly polarized with a rotation measure (RM) in the range -9 < RM < 12 rad m(-2) (95 per cent confidence level), consistent with zero. The burst was followed up with 11 telescopes to search for radio, optical, X-ray, gamma-ray and neutrino emission. Neither transient nor variable emission was found to be associated with the burst and no repeat pulses have been observed in 17.25 h of observing. The sightline to the burst is close to the Galactic plane and the observed physical properties of FRB 150215 demonstrate the existence of sight lines of anomalously low RM for a given electron column density. The Galactic RM foreground may approach a null value due to magnetic field reversals along the line of sight, a decreased total electron column density from the Milky Way, or some combination of these effects. A lower Galactic DM contribution might explain why this burst was detectable whereas previous searches at low latitude have had lower detection rates than those out of the plane.
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Kozuljevic, A. M., Bokulic, T., Grosev, D., Parashari, S., Pavelic, L., Rade, M., et al. (2026). Towards polarization-enhanced PET: Study of random background in polarization-correlated Compton events. Phys. Medica, 145, 105780–5pp.
Abstract: Background: Positron Emission Tomography (PET) is a medical imaging modality that utilizes positron-emitting isotopes for many diagnostic purposes. The positron annihilates with an electron, creating two photons of 511 keV energy and opposite momenta, entangled in their orthogonal polarizations. If each photon undergoes a Compton scattering process, the difference of their azimuthal scattering angles reflects the initial orthogonality of the polarizations, peaking at +/- 90 degrees. This correlation, not yet utilized in conventional PET scanners, offers an additional, energy-independent method for background discrimination. Methods: The correlation can be measured using single-layer Compton polarimeters, compatible with conventional PET architecture. We assembled a demonstrator with two such modules comprising 3 & times; 3 & times; 20 mm3 GAGG:Ce scintillating pixels in 16 & times; 16 matrix, read by silicon photomultipliers, mounted on a rotating gantry with 430 mm diameter. Results: This paper reports on the study of random background in measurements with Ga-68 source with activities 200-380 MBq. We compare polarization-correlated Compton events, having a two-hit signature, to conventional single-pixel hits. The signal-to-random background ratio (SBR) obtained in the polarization-correlated events is larger than the one for the single-pixel hits, for all selected event samples. We also demonstrate a correlation between the SBR and the polarimetric modulation factor. Conclusion: The random background suppression in the measurements of the polarization-correlated annihilation quanta is higher than in the standard PET modality, which could be a valuable resource for PET imaging. Since there is a correlation between the SBR and the polarimetric modulation factor, it could serve as an estimator of the random background.
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LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Lucio Martinez, M., et al. (2025). Updated measurement of CP violation and polarisation in Bs0 → J/ψ(K)over-bar*(892)0 decays. J. High Energy Phys., 10(10), 173–35pp.
Abstract: A time-integrated angular analysis of the decay B-s(0)-> J/psi(K) over bar*(892)(0), with J/psi -> mu(+)mu(-) and (K) over bar*(892)(0) -> K- pi(+), is presented. The analysis employs a sample of proton-proton collision data collected by the LHCb experiment during 2015-2018 at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6 fb(-1). A simultaneous maximum-likelihood fit is performed to the angular distributions in bins of the K-pi(+) mass. This fit yields measurements of the CP-averaged polarisation fractions and CP asymmetries for the P-wave component of the K-pi(+) system. The longitudinal and parallel polarisation fractions are determined to be f(0) = 0.534 +/- 0.012 +/- 0.009 and f(parallel to) = 0.211 +/- 0.014 +/- 0.005, respectively, where the first uncertainty is statistical and the second is systematic. The CP asymmetries are measured with 3-7% precision and are found to be consistent with zero. These measurements, along with an updated determination of the branching fraction relative to the B-0 -> J/psi K*(0) decay, are combined with previous LHCb results, providing the most precise values for these observables to date.
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