|
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.
|
|
|
Hernandez, P., Pena, C., & Romero-Lopez, F. (2019). Large Nc scaling of meson masses and decay constants. Eur. Phys. J. C, 79(10), 865–13pp.
Abstract: We perform an ab initio calculation of the Nc scaling of the low-energy couplings of the chiral Lagrangian of low-energy strong interactions, extracted from the mass dependence of meson masses and decay constants. We compute these observables on the lattice with four degenerate fermions, Nf=4, and varying number of colours, Nc=3-6, at a lattice spacing of a similar or equal to 0.075 fm. We find good agreement with the expected Nc scaling and measure the coefficients of the leading and subleading terms in the large Nc expansion. From the subleading Nc corrections, we can also infer the Nf dependence, that we use to extract the value of the low-energy couplings for different values of Nf. We find agreement with previous determinations at Nc=3 and Nf=2,3 and also, our results support a strong paramagnetic suppression of the chiral condensate in moving from Nf=2 to Nf=3.
|
|
|
Ternes, C. A., Gariazzo, S., Hajjar, R., Mena, O., Sorel, M., & Tortola, M. (2019). Neutrino mass ordering at DUNE: An extra nu bonus. Phys. Rev. D, 100(9), 093004–10pp.
Abstract: We study the possibility of extracting the neutrino mass ordering at the future Deep Underground Neutrino Experiment using atmospheric neutrinos, which will be available before the muon neutrino beam starts being operational. The large statistics of the atmospheric muon neutrino and antineutrino samples at the far detector, together with the baselines of thousands of kilometers that these atmospheric (anti) neutrinos travel, provide ideal ingredients to extract the neutrino mass ordering via matter effects in the neutrino propagation through Earth. Crucially, muon capture by argon provides excellent charge tagging, allowing us to disentangle the neutrino and antineutrino signature. This is an important extra benefit of having a liquid argon time projection chamber as a far detector, that could render an similar to 3.5 sigma extraction of the mass ordering after approximately 7 yr of exposure.
|
|
|
Vicente, A. (2019). Higgs Lepton Flavor Violating Decays in Two Higgs Doublet Models. Front. Physics, 7, 174–13pp.
Abstract: The discovery of a non-zero rate for a lepton flavor violating decay mode of the Higgs boson would definitely be an indication of New Physics. We review the prospects for such signal in Two Higgs Doublet Models, in particular for Higgs boson decays into tau μfinal states. We will show that this scenario contains all the necessary ingredients to provide large flavor violating rates and still be compatible with the stringent limits from direct searches and low-energy flavor experiments.
|
|
|
Penalva, N., Hernandez, E., & Nieves, J. (2019). Further tests of lepton flavor universality from the charged lepton energy distribution in b -> c semileptonic decays: The case of Lambda(b) -> Lambda(c) l(v)over-bar(l). Phys. Rev. D, 100(11), 113007–11pp.
Abstract: In a general framework, valid for any H -> H' l(-)(v) over bar (l) semileptonic decay, we analyze the d(2)Gamma/(d omega d cos theta(l)) and d(2)Gamma/(d omega dE(l)) distributions, with omega being the product of the hadron four-velocities, theta(l) the angle made by the three-momenta of the charged lepton and the final hadron in the W- center of mass frame and E-l the charged lepton energy in the decaying hadron rest frame. Within the Standard Model (SM), d(2)Gamma/(d omega dE(l)) proportional to (c(0) (omega) c(1) (omega)E-l/M + c(2) (omega)E-l(2)/M-2), with M the initial hadron mass. We find that c(2) (omega) is independent of the lepton flavor and thus it is an ideal candidate to look for lepton flavor universality (LFU) violations. We also find a correlation between the a(2) (omega) structure function, which governs the (cos theta(l))(2) dependence of d(2)Gamma/(d omega d cos theta(l)), and c(2) (omega). Apart from trivial kinematical and mass factors, the ratio of a(2) (omega)/c(2) (omega) is a universal function that can be measured in any semileptonic decay, involving not only b -> c transitions. These two SM predictions can be used as new tests in the present search for signatures of LFU violations. We also generalize the formalism to account for some new physics (NP) terms, and show that neither c(2) nor a(2) are modified by left and right scalar NP terms, being however sensitive to left and right vector corrections. We also find that the a(2)/c(2) ratio is not modified by these latter NP contributions. Finally, and in order to illustrate our findings, we apply our general framework to the Lambda(b) -> Lambda(c)l (v) over bar (l) decay. We show that a measurement of c(2) (or a(2)) for tau decay would not only be a direct measurement of the possible existence of NP, but it would also allow to distinguish from NP fits to b -> c tau(v) over bar (tau) anomalies in the meson sector, which otherwise give the same total and differential d Gamma/d omega widths. We show that the same occurs for the other two terms, c(0) and c(1), that appear in d(2)Gamma/(d omega dE(l)), and for the cos theta(l) linear term of the angular distribution.
|
|
|
Miralles, V., & Pich, A. (2019). LHC bounds on colored scalars. Phys. Rev. D, 100(11), 115042–11pp.
Abstract: We analyze the constraints on colored scalar bosons imposed by the current LHC data at root s = 13 TeV. Specifically, we consider an additional electroweak doublet of color-octet scalars, satisfying the principle of minimal flavor violation in order to fulfill the stringent experimental limits on flavor-changing neutral currents. We demonstrate that colored scalars with masses below 800 GeV are already excluded, provided they are not fermiophobic.
|
|
|
Babiano, V., Balibrea, J., Caballero, L., Calvo, D., Ladarescu, I., Mira Prats, S., et al. (2020). First i-TED demonstrator: A Compton imager with Dynamic Electronic Collimation. Nucl. Instrum. Methods Phys. Res. A, 953, 163228–9pp.
Abstract: i-TED consists of both a total energy detector and a Compton camera primarily intended for the measurement of neutron capture cross sections by means of the simultaneous combination of neutron time-of-flight (TOF) and gamma-ray imaging techniques. TOF allows one to obtain a neutron-energy differential capture yield, whereas the imaging capability is intended for the discrimination of radiative background sources, that have a spatial origin different from that of the capture sample under investigation. A distinctive feature of i-TED is the embedded Dynamic Electronic Collimation (DEC) concept, which allows for a trade-off between efficiency and image resolution. Here we report on some general design considerations and first performance characterization measurements made with an i-TED demonstrator in order to explore its gamma-ray detection and imaging capabilities.
|
|
|
Nieves, J., & Pavao, R. (2020). Nature of the lowest-lying odd parity charmed baryon Lambda(c)(2595) and Lambda(c)(2625) resonances. Phys. Rev. D, 101(1), 014018–17pp.
Abstract: We study the structure of the Lambda(c) (2595) and Lambda(c) (2625) resonances in the framework of an effective field theory consistent with heavy quark spin and chiral symmetries, which incorporates the interplay between Sigma(()(c)*() )pi – ND(*()) baryon-meson degrees of freedom (d.o.f.) and bare P-wave c (u) over bard quark-model states. We show that these two resonances are not heavy quark spin symmetry partners. The J(P) = 3/2(-) Lambda(c) (2625) should be viewed mostly as a dressed three-quark state, whose origin is determined by a bare state, predicted to lie very close to the mass of the resonance. The J(P) = 1/2(-) Lambda(c) (2595) seems to have, however, a predominant molecular structure. This is because it is either the result of the chiral Sigma(c)pi interaction, whose threshold is located much closer than the mass of the bare three-quark state, or because the light d.o.f. in its inner structure are coupled to the unnatural 0(-) quantum numbers. We show that both situations can occur depending on the renormalization procedure used. We find some additional states, but the classification of the spectrum in terms of heavy quark spin symmetry is difficult, despite having used interactions that respect this symmetry. This is because the bare quark-model state and the Sigma(c)pi threshold are located extraordinarily close to the Lambda(c) (2625) and Lambda(c) (2595), respectively, and hence they play totally different roles in each sector.
|
|
|
Yao, D. L., Fernandez-Soler, P., Guo, F. K., & Nieves, J. (2020). New parametrization of the form factors in (B)over-bar -> Dl(nu)over-bar(l) decays. Phys. Rev. D, 101(3), 034014–7pp.
Abstract: A new model-independent parametrization is proposed for the hadronic form factors in the semileptonic (B) over bar -> Dl (nu) over bar (l) decay. By a combined consideration of the recent experimental and lattice QCD data, we determine precisely the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-cb vertical bar = 41.01(75) x 10(-3) and the ratio R-D = BR((B) over bar -> D tau(nu) over bar (tau))/BR((B) over bar -> Dl (nu) over bar (l)) = 0.301(5). The coefficients in this parametrization, related to phase shifts by sumrulelike dispersion relations and hence called phase moments, encode important scattering information of the (B) over bar (D) over bar interactions which are poorly known so far. Thus, we give strong hints about the existence of at least one bound and one virtual (B) over bar (D) over bar S-wave 0(+) states, subject to uncertainties produced by potentially sizable inelastic effects. This formalism is also applicable for any other semileptonic processes induced by the weak b -> c transition.
|
|
|
Bruschini, R., & Gonzalez, P. (2020). Radiative decays in charmonium beyond the p/m approximation. Phys. Rev. D, 101(1), 014027–16pp.
Abstract: We analyze the theoretical description of radiative decays in charmonium. We use an elementary emission decay model to build the most general electromagnetic transition operator. We show that accurate results for the widths can be obtained from a simple quark potential model reasonably fitting the spectroscopy if the complete form of the operator is used instead of its standard p/m approximation and the experimental masses are properly implemented in the calculation.
|
|