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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2019). Extraction of form Factors from a Four-Dimensional Angular Analysis of (B)over-bar -> D*l(-)(nu)over-bar(l). Phys. Rev. Lett., 123(9), 091801–8pp.
Abstract: An angular analysis of the decay (B) over bar -> D*l(-)(nu) over bar (l), l is an element of {e, mu}, is reported using the full e(+) e(-) collision data set collected by the BABAR experiment at the Upsilon(4S) resonance. One B meson from the Upsilon(4S) -> B (B) over bar decay is fully reconstructed in a hadronic decay mode, which constrains the kinematics and provides a determination of the neutrino momentum vector. The kinematics of the semileptonic decay is described by the dilepton mass squared, q(2), and three angles. The first unbinned fit to the full four-dimensional decay rate in the standard model is performed in the so-called Boyd-Grinstein-Lebed approach, which employs a generic q(2) parametrization of the underlying form factors based on crossing symmetry, analyticity, and QCD dispersion relations for the amplitudes. A fit using the more model-dependent Caprini-Lellouch-Neubert (CLN) approach is performed as well. Our form factor shapes show deviations from previous fits based on the CLN parametrization. The latest form factors also provide an updated prediction for the branching fraction ratio R(D*) B((B) over bar -> D* tau(-)(nu) over bar (tau)) /B((B) over bar -> D*l(-)(nu) over bar (l)) = 0.253 +/- 0.005. Finally, using the well-measured branching fraction for the (B) over bar -> D*l(-)(nu) over bar (l) decay, a value of vertical bar V-cb vertical bar = (38.36 +/- 0.90) x 10(-3) is obtained that is consistent with the current world average for exclusive (B) over bar -> D(*)l(-)(nu) over bar (l) decays and remains in tension with the determination from inclusive semileptonic B decays to final states with charm.
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Beltran-Palau, P., Ferreiro, A., Navarro-Salas, J., & Pla, S. (2019). Breaking of adiabatic invariance in the creation of particles by electromagnetic backgrounds. Phys. Rev. D, 100(8), 085014–12pp.
Abstract: Particles are spontaneously created from the vacuum by time-varying gravitational or electromagnetic backgrounds. It has been proven that the particle number operator in an expanding universe is an adiabatic invariant. In this paper we show that, in some special cases, the expected adiabatic invariance of the particle number fails in presence of electromagnetic backgrounds. In order to do this, we consider as a prototype a Sauter-type electric pulse. Furthermore, we also show a close relation between the breaking of the adiabatic invariance and the emergence of the axial anomaly.
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Barenboim, G., Denton, P. B., & Oldengott, I. M. (2019). Constraints on inflation with an extended neutrino sector. Phys. Rev. D, 99(8), 083515–9pp.
Abstract: Constraints on inflationary models typically assume only the standard models of cosmology and particle physics. By extending the neutrino sector to include a new interaction with a light scalar mediator (m(phi) similar to MeV), it is possible to relax these constraints, in particular via opening up regions of the parameter space of the spectral index n(s). These new interactions can be probed at IceCube via interactions of astrophysical neutrinos with the cosmic neutrino background for nearly all of the relevant parameter space.
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Yang, W. Q., Mena, O., Pan, S., & Di Valentino, E. (2019). Dark sectors with dynamical coupling. Phys. Rev. D, 100(8), 083509–11pp.
Abstract: Coupled dark matter-dark energy scenarios arc modeled via a dimensionless parameter xi, which controls the strength of their interaction. While this coupling is commonly assumed to be constant, there is no underlying physical law or symmetry that forbids a time-dependent xi parameter. The most general and complete interacting scenarios between the two dark sectors should therefore allow for such a possibility, and it is the main purpose of this study to constrain two possible and well-motivated coupled cosmologies by means of the most recent and accurate early- and late-time universe observations. We find that CMB data alone prefer xi(z) > 0 and therefore a smaller amount of dark matter, alleviating some crucial and well-known cosmological data tensions. An objective assessment of the Bayesian evidence for the coupled models explored here shows no particular preference for the presence of a dynamical dark sector coupling.
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Ellis, J., Konoplich, R., Mavromatos, N. E., Nguyen, L., Sakharov, A. S., & Sarkisyan-Grinbaum, E. K. (2019). Robust constraint on Lorentz violation using Fermi-LAT gamma-ray burst data. Phys. Rev. D, 99(8), 083009–22pp.
Abstract: Models of quantum gravity suggest that the vacuum should be regarded as a medium with quantum structure that may have nontrivial 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. 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 nontrivial 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 x10(17) GeV, and we estimate the sensitivity attainable with additional future sources to be detected by Fermi-LAT.
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