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In the context of lepton flavor universality violation (LFUV) studies, we fully derive a general tensor formalism to investigate the role that left- and right-handed neutrino new-physics (NP) terms may have in $b\to c ��\bar��_��$ transitions. We present, for several extensions of the Standard Model (SM), numerical results for the $��_b\to��_c��\bar��_��$ semileptonic decay, which is expected to be measured with precision at the LHCb. This reaction can be a new source of experimental information that can help to confirm, or maybe rule out, LFUV presently seen in $\bar B$ meson decays. The present study analyzes observables that can help in distinguishing between different NP scenarios that otherwise provide very similar results for the branching ratios, which are our currently best hints for LFUV. Since the $��$ lepton is very short-lived, we consider three subsequent $��$-decay modes, two hadronic $����_��$ and $����_��$ and one leptonic $��\bar��_����_��$, which have been previously studied for $\bar B\to D^{(*)}$ decays. Within the tensor formalism that we have developed in previous works, we re-obtain the expressions for the differential decay width written in terms of visible (experimentally accessible) variables of the massive particle created in the $��$ decay. There are seven different $��$ angular and spin asymmetries that are defined in this way and that can be extracted from experiment. Those asymmetries provide observables that can help in constraining possible SM extensions., 43 latex pages, 4 figures, 2 tables, a few errata corrected and new comments added. Version accepted for publication in JHEP

For a general $H_b\to H_c��\bar��_��$ decay we analyze the role of the $��$ polarization vector ${\cal P}^��$ in the context of lepton flavor universality violation studies. We use a general phenomenological approach that includes, in addition to the Standard Model (SM) contribution, vector, axial, scalar, pseudoscalar and tensor new physics (NP) terms which strength is governed by, complex in general, Wilson coefficients. We show that both in the laboratory frame, where the initial hadron is at rest, and in the center of mass of the two final leptons, a $\vec {\cal P}$ component perpendicular to the plane defined by the three-momenta of the final hadron and the $��$ lepton is only possible for complex Wilson coefficients, being a clear signal for physics beyond the SM as well as time reversal (or CP-symmetry) violation. We make specific evaluations of the different polarization vector components for the $��_b\to��_c$, $\bar B_c\to��_c,J/��$ and $\bar B\to D^{(*)}$ semileptonic decays, and describe NP effects in the complete two-dimensional space associated with the independent kinematic variables on which the polarization vector depends. We find that the detailed study of ${\cal P}^��$ has great potential to discriminate between different NP scenarios for $0^-\to 0^-$ decays, but also for $��_b \to ��_c$ transitions. For this latter reaction, we pay special attention to corrections to the SM predictions derived from complex Wilson coefficients contributions., 34 latex pages, 10 figures, 1 table. Enlarged and modified discussion. New references and one new figure added

The BaBar Collaboration has recently reported branching fractions for semileptonic decays of the $B$ meson into final states with charged and neutral $D_{1}(2420)$ and $D_{2}^{\ast}(2460)$, two narrow orbitally excited charmed mesons. We evaluate these branching fractions within the framework of a constituent quark model in two steps, one which involves a semileptonic decay and the other one mediated by a strong process. Our results are in agreement with the experimental data., Contribution to the proceedings of the XIV International Conference on Hadron Spectroscopy (HADRON 2011); 13-17 June 2011, Munich, Germany

In this paper we prove the existence of a time-frequency space that best approximates a given finite set of data. Here best approximation is in the least square sense, among all time-frequency spaces with no more than a prescribed number of generators. We provide a formula to construct the generators from the data and give the exact error of approximation. The setting is in the space of square integrable functions defined on a second countable LCA group and we use the Zak transform as the main tool., 11 pages

We apply the general formalism derived in N. Penalva et al. [Phys. Rev. D 101, 113004 (2020)] to the semileptonic decay of pseudoscalar mesons containing a $b$ quark. While present $B\to D^{(*)}$ data give the strongest evidence in favor of lepton flavor universality violation, the observables that are normally considered are not able to distinguish between different new physics (NP) scenarios. In the above reference we discussed the relevant role that the various contributions to the double differential decay widths $d^2��/(d��d\cos��_\ell)$ and $d^2��/(d��dE_\ell)$ could play to this end. Here $��$ is the product of the two hadron four-velocities, $��_\ell$ is the angle made by the final lepton and final hadron three-momenta in the center of mass of the final two-lepton system, and $E_\ell$ is the final charged lepton energy in the laboratory system. The formalism was applied there to the analysis of the $��_b\to��_c$ semileptonic decay showing the new observables were able to tell apart different NP scenarios. Here we analyze the $\bar B_c\to ��_c ��\bar��_��$, $\bar B_c\to J/����\bar��_��$, $\bar B\to D��\bar��_��$ and $\bar B\to D^*��\bar��_��$ semileptonic decays. We show that, as a general rule, the $\bar B_c \to J/��$ observables, even including $��$ polarization, are less optimal for distinguishing between NP scenarios than those obtained from $\bar B_c \to ��_c$ decays, or those presented in N. Penalva et al. for the related $��_b \to ��_c$ semileptonic decay. Finally, we show that $\bar B\to D$ and $\bar B_c\to ��_c$, and $\bar B\to D^*$ and $\bar B_c\to J/��$ decay observables exhibit similar behaviors., 28 latex pages, 26 figures, 2 tables, a new reference added and a few misprints corrected

Understanding single pion production reactions on free nucleons is the first step towards a correct description of these processes in nuclei, which are important for signal and background contributions in current and near future accelerator neutrino oscillation experiments. In this work, we reanalyze our previous studies of neutrino-induced one-pion production on nucleons for outgoing $��N$ invariant masses below 1.4 GeV. Our motivation is to get a better description of the $��_��n\to��^- n��^+$ cross section, for which current theoretical models give values significantly below data. This channel is very sensitive to the crossed $��(1232)$ contribution and thus to spin 1/2 components in the Rarita-Schwinger $��$ propagator. We show how these spin 1/2 components are nonpropagating and give rise to contact interactions. In this context, we point out that the discrepancy with experiment might be corrected by the addition of appropriate extra contact terms and argue that this procedure will provide a natural solution to the $��_��n\to��^- n��^+$ puzzle. To keep our model simple, in this work we propose to change the strength of the spin 1/2 components in the $��$ propagator and use the $��_��n\to��^- n��^+$ data to constraint its value. With this modification, we now find a good reproduction of the $��_��n\to��^- n��^+$ cross section without affecting the good results previously obtained for the other channels. We also explore how this change in the $��$ propagator affects our predictions for pion photoproduction and find also a better agreement with experiment than with the previous model., 21 pages, 1 Table, 8 Figures. Enlarged introduction and discussion. One new figure, One new panel in Figure 1

We present a new determination of the $N��$ axial form factors from neutrino induced pion production data. For this purpose, the model of Hernandez {\it et al.} [Phys. Rev. D76, 033005 (2007)] is improved by partially restoring unitarity. This is accomplished by imposing Watson's theorem on the dominant vector and axial multipoles. As a consequence, a larger $C_5^A(0)$, in good agreement with the prediction from the off-diagonal Goldberger-Treiman relation, is now obtained., 17 latex pages, 7 figures, 2 tables. Some typos corrected

We reevaluate the $B\to��\,l^+��_l$ decay width as a full $B\to����\,l^+��_l$ four-particle decay, in which the two final pions are produced via an intermediate $��$ meson. The decay width can be written as a convolution of the $B\to��\,l^+��_l$ decay width, for an off-shell $��$, with the $��\to����$ line shape. This allows to fully incorporate the effects of the finite $��$ meson width. As shown, consideration of the $��$ meson width effects increase the $|V_{ub}|$ value by some 8%, rendering it in better agreement with the determination based in the $B\to��$ decay. We take the $q^2$ dependence of the $B\to ��$ semileptonic form factors from a dispersive Omn��s representation. The Omn��s subtraction constants and the overall normalization parameter $|V_{ub}|$ are fitted to light cone sum rules and lattice QCD theoretical form-factor calculations, in the low and high $q^2$ regions respectively, together to the CLEO, BaBar and Belle experimental partial branching fraction distributions. The extracted value from this global fit is $|V_{ub}|=(3.12\pm 0.13)\times 10^{-3}$, in agreement with the average $B\to ��$ exclusive value $|V_{ub}|=(3.23\pm 0.31)\times 10^{-3}$ quoted by the Particle Data Group. The extracted value increases to $|V_{ub}|=(3.51\pm 0.16)\times 10^{-3}$ if only the most recent Belle Collaboration data is used. This latter value is in agreement with different theoretical determinations based in the $B\to��$ semileptonic decay and the values obtained by the CKMfitter and UTfit groups. In any case a clear tension with the $|V_{ub}|$ value extracted from inclusive semileptonic $b\to u$ decays still persists., 13 latex pages, 3 figures, 3 tables. We have corrected a misinterpretation of experimental data on partial branching fractions. Results are modified but main conclusion remains the same

We study the $f^+$ form factor for the $\bar B_s\to K^+\ell^-\bar��_\ell$ semileptonic decay in a nonrelativistic quark model. The valence quark contribution is supplemented with a $\bar B^*$-pole term that dominates the high $q^2$ region. To extend the quark model predictions from its region of applicability near $q^2_{\rm max}=(M_{B_s}-M_K)^2$, we use a multiply-subtracted Omn��s dispersion relation. We fit the subtraction constants to a combined input from previous light cone sum rule results in the low $q^2$ region and the quark model results (valence plus $\bar B^*$-pole) in the high $q^2$ region. From this analysis, we obtain $��(\bar B_s\to K^+\ell^-\bar��_\ell)=(5.47^{+0.54}_{-0.46})|V_{ub}|^2\times 10^{-9}\,{\rm MeV}$, which is about 10% and 20% higher than predictions based on Lattice QCD and QCD light cone sum rules respectively., 4 latex pages, 3 figures, 1 table. Talk presented at the "XI International Conference on Hyperons, Charm and Beauty Hadrons (BEACH 2014)", Birmingham (U.K.), July 2014

We compare our pion production results with recent MiniBooNE data measured in mineral oil. Our total cross sections lie below experimental data for neutrino energies above 1 GeV. Differential cross sections show our model produces too few high energy pions in the forward direction as compared to data. The agreement with experiment improves by artificially removing pion final state interaction., 4 Latex pages, 6 figures. Talk given at the International Workshop on Neutrino Factories, Super beams and Beta Beams (NUFACT 2013), Beijing, August 2013

We present results for exclusive $b\to c$ semileptonic decays of ground state triply-heavy baryons and for semileptonic $c\to s,d$ decays of doubly heavy ground state $cb$ baryons. In both cases, we have derived for the first time heavy quark spin symmetry relations for the hadronic amplitudes near zero recoil. Though strictly valid in the limit of very large heavy quark masses and near zero recoil, they turn out to be reasonable accurate for the whole available phase space in these decays and for the actual heavy quark masses we use. With these relations we have made approximate, but model independent, predictions for ratios of decay widths. In the case of spin-1/2 $cb$ baryons, we find that hyperfine mixing in the wave function has a great impact on their $c\to s,d$ decay widths., 8 Latex pages, 5 Tables. Contribution to "Xth Quark Confinement and the Hadron Spectrum"

We evaluate exclusive semileptonic decays of ground-state spin-1/2 and spin-3/2 doubly heavy $cb$ baryons driven by a $c\to s,d$ transition at the quark level. We check our results for the form factors against heavy quark spin symmetry constraints obtained in the limit of very large heavy quark masses and near zero recoil. Based on those constraints we make model independent, though approximate, predictions for ratios of decay widths., 25 latex pages, 4 figures, 5 tables, misprints corrected. arXiv admin note: text overlap with arXiv:1108.1296

We evaluate exclusive semileptonic decays of ground-state spin-1/2 doubly heavy charmed baryons driven by a $c\to s,d$ transition at the quark level. Our results for the form factors are consistent with heavy quark spin symmetry constraints which are valid in the limit of an infinitely massive charm quark and near zero recoil. Only a few exclusive semileptonic decay channels have been theoretically analyzed before. For those cases we find that our results are in a reasonable agreement with previous calculations., 13 latex pages, 3 figures, 2 tables. A new figure added, corrected misprints

We observe amplification of spin-wave packets propagating along a film of yttrium iron garnet (YIG) subject to a transverse temperature gradient. The amplification is attributed to a spin-transfer thermal torque created by spin currents generated by means of the spin Seebeck effect that acts on the magnetization and opposes the relaxation. The experimental data are interpreted with a simple theoretical model using spin-wave theory that gives an amplification gain in very good agreement with measurements., 8 pages, 8 figures This paper has been withdrawn by the author in order to be rewriten!

We present results for the strong widths corresponding to the $��_b\to ��_b\, ��$ and $��_b^{*}\to ��_b\, ��$ decays. We apply our model in Ref. Phys. Rev. D 72, 094022 (2005) where we previously studied the corresponding transitions in the charmed sector. Our non-relativistic constituent quark model uses wave functions that take advantage of the constraints imposed by heavy quark symmetry. Partial conservation of axial current hypothesis allows us to determine the strong vertices from an analysis of the axial current matrix elements., 6 latex pages, 1 table, new references added

We re-evaluate our model predictions in Phys. Rev. D 79, 013002 (2009) for different observables in neutrino induced coherent pion production. This comes as a result of the new improved fit to old bubble chamber data of the dominant axial C_5^A nucleon-to-Delta form factor. We find an increase of 20%-30% in the values for the total cross sections. Uncertainties induced by the errors in the determination of C_5^A are computed. Our new results turn out to be compatible within about $1��$ with the former ones. We also stress the existing tension between the recent experimental determination of the ��(CC coh ��^+)}/��(NC coh ��^0)} $ ratio by the SciBooNE Collaboration and the theoretical predictions., 3 latex pages, 1 figure. Talk given at the NuFact10 Conference

We review the Rein--Sehgal model and criticize its use for low energy neutrino induced coherent pion production. We have studied the validity of the main approximations implicit in that model, trying to compare with physical observables when that is possible and with microscopical calculations. Next, we have tried to elaborate a new improved model by removing the more problematic approximations, while keeping the model still reasonably simple. Last, we have discussed the limitations intrinsic to any approach based on the partial conservation of the axial current hypothesis. In particular, we have shown the inability of such models to determine the angular distribution of the outgoing pion with respect to the direction of the incoming neutrino, except for the $q^2= 0$ kinematical point., 19 latex pages, 7 figures, 1 table. Version accepted for publication in Physical Review D

We evaluate masses and semileptonic decay widths for the ground state of doubly heavy $\Xi$ and $\Omega$ baryons in the framework of a nonrelativistic quark model. We solve the three-body problem by means of a variational ansatz made possible by heavy-quark spin symmetry constraints. Our masses are comparable to the ones obtained in relativistic calculations and we get one of the best agreements with lattice data. Our simple wave functions are used to evaluate semileptonic decays of doubly heavy $\Xi, \Xi'(J=1/2)$ and $\Omega, \Omega'(J=1/2)$ baryons. Our results for the decay widths are in reasonable agreement with calculations done in a relativistic calculation in the quark-diquark approximation. We also check that our wave functions comply with what it is expected in the infinite heavy quark mass limit., Comment: 3 latex pages, two tables. To appear in the INPC07 proceedings

The semileptonic $B\to ��l^+ ��_l$ decay is studied starting from a simple quark model which includes the influence of the $B^*$ pole. To extend the predictions of a nonrelativistic constituent quark model from its region of applicability near $q^2_{\rm max}=(m_B-m_��)^2$ to all $q^2$ values accessible in the physical decay, we use a novel multiply-subtracted Omn��s dispersion relation, which considerably diminishes the form factor dependence on the elastic $��B \to ��B$ scattering amplitudes at high energies. By comparison to the experimental branching fraction we extract $|V_{ub}| = 0.0034 \pm 0.0003 ({\rm exp}) \pm 0.0007 ({\rm theory})$. To further test our framework, we also study $D\to ��$ and $D\to K$ decays and find excellent results $\frac{f^+_��(0)}{f^+_K(0)} = 0.80 \pm 0.03, \quad \frac{{\cal B}(D^0\to ��^- e^+ ��_e)}{{\cal B}(D^0\to K^- e^+ ��_e)}= 0.079 \pm 0.008$. In particular for the $D\to ��$ case, we reproduce, with high accuracy, the three-flavor lattice QCD results recently obtained by the Fermilab-MILC-HPQCD Collaboration. While for the $D\to K$ case, we successfully describe the data for $f^+(q^2)/f^+(0)$ recently measured by the FOCUS Collaboration., 17 pages, minor modifications. Accepted in PRD

We propose a Hamiltonian model that describes the interaction between a vortex line in superfluid $^{4}$He and the gas of elementary excitations. An equation of irreversible motion for the density operator of the vortex, regarded as a macroscopic quantum particle with a finite mass, is derived in the frame of Generalized Master Equations. This enables us to cast the effect of the coupling as a drag force with one reactive and one dissipative component, in agreement with the assumption of the phenomenological theories of vortex mutual friction in the two fluid model., 16 pages, no figures, to be published in PRB

In this talk we cover several issues concerning pion production. The first one is the p p ----> p p pi^0 reaction where an alternative explanation based on the off shell extrapolation of the pi N amplitude is offered. A recent model for the gamma N ----> pi pi N reaction is presented and a new kind of exchange current is constructed from it which allows one to address problems like double Delta photoproduction from the deuteron. Finally the (gamma, pi pi) reaction in nuclei is studied and shown to be highly sensitive to the renormalization of the pions in nuclei., 12 pages (10 figures), TeX, Version 3.141 [PD VMS 3.4/CERN 1.0] (fbssuppl.sty and psfig.sty are used)