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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2015). Collins asymmetries in inclusive charged KK and K pi pairs produced in e(+)e(-) annihilation. Phys. Rev. D, 92(11), 111101–8pp.
Abstract: We present measurements of Collins asymmetries in the inclusive process e(+)e(-) -> h(1)h(2)X, h(1)h(2) = KK, K pi, pi pi, at the center-of-mass energy of 10.6 GeV, using a data sample of 468 fb(-1) collected by the BABAR experiment at the PEP-II B factory at SLAC National Accelerator Center. Considering hadrons in opposite thrust hemispheres of hadronic events, we observe clear azimuthal asymmetries in the ratio of unlike sign to like sign, and unlike sign to all charged h(1)h(2) pairs, which increase with hadron energies. The K pi asymmetries are similar to those measured for the pi pi pairs, whereas those measured for high-energy KK pairs are, in general, larger.
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T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Izmaylov, A., Novella, P., Sorel, M., & Stamoulis, P. (2017). Search for Lorentz and CPT violation using sidereal time dependence of neutrino flavor transitions over a short baseline. Phys. Rev. D, 95(11), 111101–9pp.
Abstract: A class of extensions of the Standard Model allows Lorentz and CPT violations, which can be identified by the observation of sidereal modulations in the neutrino interaction rate. A search for such modulations was performed using the T2K on-axis near detector. Two complementary methods were used in this study, both of which resulted in no evidence of a signal. Limits on associated Lorentz and CPT-violating terms from the Standard Model extension have been derived by taking into account their correlations in this model for the first time. These results imply such symmetry violations are suppressed by a factor of more than 10(20) at the GeV scale.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2019). Search for B- -> Lambda(p)over-bar nu(nu)over-bar with the BABAR experiment. Phys. Rev. D, 100(11), 111101–8pp.
Abstract: A search for the rare flavor-changing neutral current process B- -> Lambda(p) over bar nu(nu) over bar using data from the BABAR experiment has been performed. A total of 424 fb(-1) of e(+) e(-) collision data collected at the center-of-mass energy of the Upsilon(4S) resonance is used in this study, corresponding to a sample of (471 +/- 3) x 10(6) B (B) over bar pairs. Signal B- -> Lambda(p) over bar nu(nu) over bar candidates arc identified by fast fully reconstructing a B+ decay in one of many possible exclusive decays to hadronic final states, then examining detector activity that is not associated with this reconstructed B+ decay for evidence of a signal B- -> Lambda(p) over bar nu(nu) over bar decay. The data yield is found to be consistent with the expected background contribution under a null signal hypothesis, resulting in an upper limit of B(B- -> Lambda(p) over bar nu(nu) over bar) < 3.0 x 10(-5) at the 90% confidence level.
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Agullo, I., Navarro-Salas, J., Olmo, G. J., & Parker, L. (2010). Reply to "Comment on 'Insensitivity of Hawking radiation to an invariant Planck-scale cutoff' ''. Phys. Rev. D, 81(10), 108502–3pp.
Abstract: We clarify the relationship between the conclusions of the previous Comment of A. Helfer [A. Helfer, preceding Comment, Phys. Rev. D 81, 108501 (2010)] and that of our Brief Report [I. Agullo, J. Navarro-Salas, G. J. Olmo, and L. Parker, Phys. Rev. D 80, 047503 (2009).].
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Agullo, I., Navarro-Salas, J., Olmo, G. J., & Parker, L. (2011). Remarks on the renormalization of primordial cosmological perturbations. Phys. Rev. D, 84(10), 107304–5pp.
Abstract: We briefly review the need to perform renormalization of inflationary perturbations to properly work out the physical power spectra. We also summarize the basis of (momentum-space) renormalization in curved spacetime and address several misconceptions found in recent literature on this subject.
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del Rio, A., & Agullo, I. (2023). Chiral fermion anomaly as a memory effect. Phys. Rev. D, 108(10), 105025–22pp.
Abstract: We study the nonconservation of the chiral charge of Dirac fields between past and future null infinity due to the Adler-Bell-Jackiw chiral anomaly. In previous investigations [A. del Rio, Phys. Rev. D 104, 065012 (2021)], we found that this charge fails to be conserved if electromagnetic sources in the bulk emit circularly polarized radiation. In this article, we unravel yet another contribution coming from the nonzero, infrared “soft” charges of the external, electromagnetic field. This new contribution can be interpreted as another manifestation of the ordinary memory effect produced by transitions between different infrared sectors of Maxwell theory, but now on test quantum fields rather than on test classical particles. In other words, a flux of electromagnetic waves can leave a memory on quantum fermion states in the form of a permanent, net helicity. We elaborate this idea in both 1 + 1 and 3 + 1 dimensions. We also show that, in sharp contrast, gravitational infrared charges do not contribute to the fermion chiral anomaly.
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del Rio, A., & Ester, E. A. (2024). Electrically charged black hole solutions in semiclassical gravity and dynamics of linear perturbations. Phys. Rev. D, 109(10), 105022–23pp.
Abstract: We explore quantum corrections of electrically charged black holes subject to vacuum polarization effects of fermion fields in QED. Solving this problem exactly is challenging so we restrict to perturbative corrections that one can obtain using the heat kernel expansion in the one -loop effective action for electrons. Starting from the corrections originally computed by Drummond and Hathrell, we solve the full semiclassical Einstein -Maxwell system of coupled equations to leading order in Planck 's constant and find a new electrically charged, static black hole solution. To probe these quantum corrections, we study electromagnetic and gravitational (axial) perturbations on this background and derive the coupled system of Regge-Wheeler master equations that govern the propagation of these waves. In the classical limit, our results agree with previous findings in the literature. We finally compare these results with those that one can obtain by working out the Euler-Heisenberg effective action. We find again a new electrically charged static black hole spacetime and derive the coupled system of Regge-Wheeler equations governing the propagation of axial electromagnetic and gravitational perturbations. Results are qualitatively similar in both cases. We briefly discuss some challenges found in the numerical computation of the quasinormal mode frequency spectra when quantum corrections are included.
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Balbinot, R., Fabbri, A., Dudley, R. A., & Anderson, P. R. (2019). Particle production in the interiors of acoustic black holes. Phys. Rev. D, 100(10), 105021–13pp.
Abstract: Phonon creation inside the horizons of acoustic black holes is investigated using two simple toy models. It is shown that, unlike what occurs in the exterior regions, the spectrum is not thermal. This nonthermality is due to the anomalous scattering that occurs in the interior regions.
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Beltran-Palau, P., Navarro-Salas, J., & Pla, S. (2020). Adiabatic regularization for Dirac fields in time-varying electric backgrounds. Phys. Rev. D, 101(10), 105014–15pp.
Abstract: The adiabatic regularization method was originally proposed by Parker and Fulling to renormalize the energy-momentum tensor of scalar fields in expanding universes. It can be extended to renormalize the electric current induced by quantized scalar fields in a time-varying electric background. This can be done in a way consistent with gravity if the vector potential is considered as a variable of adiabatic order one. Assuming this, we further extend the method to deal with Dirac fields in four space-time dimensions. This requires a self-consistent ansatz for the adiabatic expansion, in presence of a prescribed time-dependent electric field, which is different from the conventional expansion used for scalar fields. Our proposal is consistent, in the massless limit, with the conformal anomaly. We also provide evidence that our proposed adiabatic expansion for the fermionic modes parallels the Schwinger-DeWitt adiabatic expansion of the two-point function. We give the renormalized expression of the electric current and analyze, using numerical and analytical tools, the pair production induced by a Sauter-type electric pulse. We also analyze the scaling properties of the current for a large field strength.
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Ferreiro, A., Navarro-Salas, J., & Pla, S. (2020). R-summed form of adiabatic expansions in curved spacetime. Phys. Rev. D, 101(10), 105011–12pp.
Abstract: The Feynman propagator in curved spacetime admits an asymptotic (Schwinger-DeWitt) series expansion in derivatives of the metric. Remarkably, all terms in the series containing the Ricci scalar R can be summed exactly. We show that this (nonperturbative) property of the Schwinger-DeWitt series has a natural and equivalent counterpart in the adiabatic (Parker-Fulling) series expansion of the scalar modes in an homogeneous cosmological spacetime. The equivalence between both R-summed adiabatic expansions can be further extended when a background scalar field is also present.
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