arXiv subjects

C. Barbero

Publications and source records attributed to C. Barbero.

At least 19 recordsLinked to original sources

arXiv2024

Sparse Reconstruction of Wavefronts using an Over-Complete Phase Dictionary

Wavefront reconstruction is a critical component in various optical systems, including adaptive optics, interferometry, and phase contrast imaging. Traditional reconstruction methods often employ either the Cartesian (pixel) basis or the Zernike polynomial basis. While the Cartesian basis is adept at capturing high-frequency features, it is susceptible to overfitting and inefficiencies due to the high number of degrees of freedom. The Zernike basis efficiently represents common optical aberrations but struggles with complex or non-standard wavefronts such as optical vortices, Bessel beams, or wavefronts with sharp discontinuities. This paper introduces a novel approach to wavefront reconstruction using an over-complete phase dictionary combined with sparse representation techniques. By constructing a dictionary that includes a diverse set of basis functions - ranging from Zernike polynomials to specialized functions representing optical vortices and other complex modes - we enable a more flexible and efficient representation of complex wavefronts. Furthermore, a trainable affine transform is implemented to account for misalignment. Utilizing principles from compressed sensing and sparse coding, we enforce sparsity in the coefficient space to avoid overfitting and enhance robustness to noise.

physics.optics↗

arXiv2016

Inconsistency of the interactions between pseudoscalar, spinor and Rarita-Schwinger fields

We perform the Dirac quantization of RS fields interacting with a spinor and the first derivative of a pseudoscalar field. We achieve the calculations for two forms of this interaction: first we review the conventional coupling of lowest derivative order, reproducing the well known inconsistencies in its anticommutator algebra. Then, we perform the analysis on the next order term popularly known as spin 3/2 gauge invariant interaction, which is claimed to be free of these inconsistencies. Nevertheless we find that the direct application of the Dirac formalism leads to inconsistencies in complete analogy to the previous case. This is of high relevance in the particle phenomenology field, where these interactions are used to interpret experimental data involving Delta(1232) resonances.

nucl-th↗

arXiv2015

About consistence between pi N Delta spin-3/2 gauge couplings and electromagnetic gauge invariance

We analyze the consistence between the recently proposed "spin 3/2 gauge" interaction for the Delta resonance with nucleons and pions, and the fundamental electromagnetic gauge invariance in any radiative amplitude. Chiral symmetric pion-derivative pi N Delta couplings can be substituted through a linear transformation to get Delta-derivative ones, which have the property of decoupling the 1/2 field components of the Delta propagator. Nevertheless, the electromagnetic gauge invariance introduced through minimal substitution in all derivatives, can only be fulfilled at a given order n without destroying the spin 3/2 one by dropping n+1 order terms within an effective field theory (EFT) framework with a defined power counting. In addition, we show that the Ward identity for the gamma Delta gamma vertex cannot be fulfilled with a trimmed 3/2 propagator, which should be necessary in order to keep the spin 3/2 gauge symmetry in the radiative case for the gamma Delta gamma amplitude. Finally, it is shown that radiative corrections of the spin 3/2 gauge strong vertexes at one loop, reintroduce the conventional interaction.

nucl-th↗

arXiv2013

One pion production in neutrino-nucleon scattering and the different parametrizations of the weak $N\rightarrowΔ$ vertex

The $N \to Δ$ weak vertex provides an important contribution to the one pion production in neutrino-nucleon and neutrino-nucleus scattering for $πN$ invariant masses below 1.4 GeV. Beyond its interest as a tool in neutrino detection and their background analyses, one pion production in neutrino-nucleon scattering is useful to test predictions based on the quark model and other internal symmetries of strong interactions. Here we try to establish a connection between two commonly used parametrizations of the weak $N \to Δ$ vertex and form factors (FF) and we study their effects on the determination of the axial coupling $C_5^A(0)$, the common normalization of the axial FF, which is predicted to hold 1.2 by using the PCAC hypothesis. Predictions for the $ν_μ p \to μ^- pπ^+$ total cross sections within the two approaches, which include the resonant $Δ^{++}$ and other background contributions in a coherent way, are compared to experimental data.

nucl-th↗

arXiv2013

2p2h effects on the weak pion production cross section

The neutrino-nucleon --> lepton pion QE reaction on the A-target is used as a signal event or/and to reconstruct the neutrino energy, using two-body kinematics. Competition of another processes could lead to misidentification of the arriving neutrinos, being important the fake events coming from the CC1-pion background. A precise knowledge of cross sections is a prerequisite in order to make simulations in event generators to substract the fake ones from the QE countings, and in this contribution we analyze the different nuclear effects on the CC1-pion channel. Our calculations also can be extended for the NC case.

nucl-th↗

arXiv2013

Matrix elements of four-quark operators and ΔL=2 hyperon decays

The study of neutrinoless double beta decays of nuclei and hyperons require the calculation of hadronic matrix elements of local four-quark operators that change the total charge by two units ΔQ=2 . Using a low energy effective Lagrangian that induces these transitions, we compute these hadronic matrix elements in the framework of the MIT bag model. As an illustrative example we evaluate the amplitude and transition rate of Σ- -> p e- e-, a decay process that violates lepton number by two units (ΔL=2). The relevant matrix element is evaluated without assuming the usual factorization approximation of the four-quark operators and the results obtained in both approaches are compared.

hep-ph↗

arXiv2012

Single photon production $ν_l N\rightarrow ν_l N γ$ in neutrino-nucleon scattering

The quasielastic charged current (CCQE) $ν_e n \rightarrow e^- p$ scattering is the dominant mechanism to detect appearance of a $ν_e$ in an almost $ν_μ$ flux at the 1 GeV scale. Actual experiments show a precision below 1% and between less known background contributions, but necessary to constraint the event excess, we have the radiative corrections. A consistent model recently developed for the simultaneous description of elastic and radiative $πN$ scattering, pion-photoproduction and single pion production processes, both for charged and neutral current neutrino-nucleon scattering, is extended for the evaluation of the radiative $ν_l N\rightarrow ν_l N γ$ cross section. Our results are similar to a previous (but inconsistent) theoretical evaluation in the low energy region, and show an increment in the upper region where the $Δ$ resonance becomes relevant.

nucl-th↗

arXiv2012

Nonmesonic Hyperon Weak Decay Spectra in $^{12}_Λ$C}

We study the nonmesonic weak decay (NMWD) $ΛN \to nN$ of the ${}^{12}_Λ C$ hypernucleus induced by the nucleon $N=n,p$ with transition rate $Γ_N$. The nuclear process is described by the interplay of two models; one describing the NMWD of hyperon $Λ$ in the nuclear environment, and the other taking into account the Final State Interaction (FSI) of the two outgoing nucleons with the residual nucleus. The first one is done in the framework of the Independent-Particle Shell-Model (IPSM), with the decay dynamics represented by the exchange of $π+ η+ K+ρ+ω+K^*$ mesons with usual parametrization. For the second one is used a time dependent multicollisional intranuclear cascade schema (implemented in the CRISP code - Collaboration Rio-São Paulo). The results obtained for inclusive and exclusive kinetic energy spectra, and the angular correlation are compared with recent data from KEK and FINUDA experiments. The calculated ratio $(Γ_n / Γ_p)^{\partial{\tiny FSI}}$, between the numbers of emitted back-to-back $nn$ and $np$ pairs, is in good agreement with the experimental data.

nucl-th↗

arXiv2010

Evaluation of coincidence number of pairs and asymmetry parameter in nonmesonic hypernuclear decay

We develop a theoretical framework for the evaluation of the coincidence number of pairs, $N_{nN}$, and the asymmetry parameter, $a_Λ$, in nonmesonic hypernuclear decay $ΛN\rightarrow nN$. The primary nomesonic weak hyperon-nucleon decay process is described through the independent particle shell model. When the effect of the strong interactions experimented by the two nucleons leaving the residual nucleus is included, we have in addition to the $2p1h$ primary configuration $2p'1h'$, $3p2h$, $4p3h$, $\cdots$, etc secondary ones. We work within the $2p'1h'$ subspace of final states assuming a simple approach for finite nuclei based on the eikonal approximation. An optical potential including the nucleon-nucleus isoscalar and isovector interaction is introduced to take into account the minimum nuclear medium effects and to describe the nucleon-nucleus dispersion process along the outgoing path. We applied the proposed description to the calculation of the observables in $^{5}_ΛHe$ and $^{12}_ΛC$ nonmesonic decays. The calculated results show that our treatment of FSI even considered as restricted to a subspace of states gives a good agreement with experimental data, similar to that ones presented by more elaborated evaluations. This indicates that the developed theoretical scheme seems to be appropriated to include more complex configurations. We also discuss the ground state normalization effects at the moment of including the two-nucleon induced decay ($ΛNN \rightarrow nNN$) contribution.

nucl-th↗

arXiv2007

$ΔL=2$ hyperon semileptonic decays

We compute the rates of semileptonic B_A \to B_Bl^-l^- (l=e or μ) hyperon transitions in a model where intermediate states involve loops of baryons and a Majorana neutrino. These rates turn out to be well below present experimental bounds and other theoretical estimates. From the experimental upper limit on the Ξ^- \to pμ^-μ^- decay, we derive the bound < 22 TeV for the effective Majorana mass of the muon neutrino. Also, an estimate of background contributions for these decays due to the allowed B_A \to B_Bl^-l^-\barν\barν decays are provided.

hep-ph↗

arXiv2005

$σ$ meson exchange effect on nonmesonic hypernuclear weak decay observables

We analyze the influence of $σ$ meson exchange on the main nonmesonic hypernuclear weak decay observables: the total rate, $Γ_{NM}$, the neutron-to-proton branching ratio, $Γ_{n/p}$, and the proton asymmetry parameter, $a_Λ$. The $σ$ meson exchange is added to the standard strangeness-changing weak $ΛN\to NN$ transition potential, which includes the exchange of the complete pseudoscalar and vector mesons octet ($π$, $η$, $K$, $ρ$, $ω$, $K^*$). Using a shell model formalism, the $σ$ meson weak coupling constants are adjusted to reproduce the recent $Γ_{NM}$ and $Γ_{n/p}$ experimental data for $^5_ΛHe$. Numerical results for the remaining observables of $^5_ΛHe$ and all the observables of $^{12}_ΛC$ decays are presented. They clearly show that the addition of the $σ$ meson, in spite of improving some observables values, is not enough to reproduce simultaneously all the measurements, and the puzzle posed by the experimental data remains unexplained.

nucl-th↗

arXiv2003

Kinematical and nonlocality effects on the nonmesonic weak hypernuclear decay

We derive in detail the transition potential for nonmesonic lambda-hypernuclear decay in a one-meson-exchange model involving the full pseudoscalar and vector meson octets and including two effects that have been systematically omitted in the literature. These are the kinematical effects due to the difference between the lambda and nucleon masses and the first-order nonlocality corrections. Numerical results for $^{12}_Λ$C and $^5_Λ$He are presented and they show that the combined kinematical plus nonlocal corrections have an appreciable influence on the partial decay rates. However, this is somewhat diminished in the main decay observables: the total nonmesonic rate, the neutron-to-proton branching ratio, and the asymmetry parameter. The latter two still cannot be reconciled with the available experimental data. The existing theoretical predictions for the sign of the asymmetry parameter in $^5_Λ$He are confirmed.

nucl-th↗

arXiv2002

Double beta decay of sigma^- hyperons

We compute the strangeness-conserving double beta decay of $Σ^-$ hyperons, which is the only hadronic system that can undergo such decays. We consider both, the lepton number conserving %$Σ^-\go Σ^++2e^-+2 \barν$ $Σ^-\go Σ^+e^-e^-\barν\barν$ ($ββ_{Σ_{2ν}}$) and the lepton number violating $Σ^-\go Σ^+e^-e^-$ ($ββ_{Σ_{0ν}}$) modes. The branching ratios of these $ββ$ decays are suppressed at the level of $10^{-30}$ considering a light neutrino scenario in the case of the $ββ_{Σ_{0ν}}$ channel. The dynamical origin of such low rates and their possible enhancements are briefly discussed. Given its simplicity those decays can be used also for the purposes of illustrating the main features of double beta decays.

nucl-th↗

arXiv2002

Hypernuclear Weak Decay Puzzle

A general shell model formalism for the nonmesonic weak decay of the hypernuclei has been developed. It involves a partial wave expansion of the emitted nucleon waves, preserves naturally the antisymmetrization between the escaping particles and the residual core, and contains as a particular case the weak $Λ$-core coupling formalism. The Extreme Particle-Hole Model and the Quasiparticle Tamm-Dancoff Approximation are explicitly worked out. It is shown that the nuclear structure manifests itself basically through Pauli Principle, and a very simple expression is derived for the neutron and proton induced decays rates, $Γ_n$ and $Γ_p$, which does not involve the spectroscopic factors. We use the standard strangeness-changing weak $ΛN\to NN$ transition potential which comprises the exchange of the complete pseudoscalar and vector meson octets ($π,η,K,ρ,ω,K^*$), taking into account some important parity violating transition operators that are systematically omitted in the literature. The interplay between different mesons in the decay of ${^{12}_ΛC}$ is carefully analyzed. With the commonly used parametrization in the One-Meson-Exchange Model (OMEM), the calculated rate $Γ_{NM}= Γ_n+Γ_p$ is of the order of the free $Λ$ decay rate $Γ^0(Γ_{NM}^{\rm th}\cong Γ^0)$ and is consistent with experiments. Yet, the measurements of $Γ_{n/p}=Γ_n/Γ_p$ and of $Γ_p$ are not well accounted for by the theory ($Γ_{n/p}^{\rm th}\lsim 0.42; Γ_p^{\rm th}\gsim 0.60 Γ^0$). It is suggested that, unless additional degrees of freedom are incorporated, the OMEM parameters should be radically modified.

nucl-th↗

arXiv1999

Nuclear moments for the neutrinoless double beta decay II

The recently developed formalism for the evaluation of nuclear form factors in neutrinoless double beta decay is applied to $^{48}Ca$, $^{76}Ge$, $^{82}Se$, $^{100}Mo$, $^{128}Te$ and $^{130}Te$ nuclei. Explicit analytical expressions that follows from this theoretical development, in the single mode model for the decay of $^{48}Ca$, have been worked out. They are useful both for testing the full numerical calculations, and for analytically checking the consistency with other formalisms. Large configuration space calculations are compared with previous studies, where alternative formulations were used. Yet, besides using the G-matrix as residual interaction, we here use a simple $δ$-force. Attention is paid to the connected effects of the short range nuclear correlations and the finite nucleon size. Constraints on lepton number violating terms in the weak Hamiltonian (effective neutrino Majorana mass and effective right-handed current coupling strengths) are deduced.

nucl-th↗

arXiv1998

Weak Magnetism in Two Neutrino Double Beta Decay

We have extended the formalism for the two-neutrino double beta decay by including the weak-magnetism term, as well as other second-forbidden corrections. The weak magnetism diminishes the calculated half-lives in $\sim 10%$, independently of the nuclear structure. Numerical computations were performed within the pn-QRPA, for $^{76}Ge$, $^{82}Se$, $^{100} Mo$, $^{128}Te$ and $^{130}Te$ nuclei. No one of the second-forbidden corrections modifies significantly the spectrum shapes. The total reduction in the calculated half lives varies from 6% up to 32%, and strongly depend on the nuclear interaction in the particle-particle $S=1,T=0$ channel. We conclude that the higher order effects in the weak Hamiltonian would hardly be observed in the two-neutrino double beta experiments.

nucl-th↗

arXiv1998

Competition between standard and exotic double beta decays

We discuss the contributions of higher order terms in weak Hamiltonian to the standard two-neutrino double beta decay. The formalism for the unique first forbidden transitions has been developed, and it is shown that they can alter the two-electron energy spectrum. Yet, their effect is too small to screen the detection of exotic neutrinoless double beta decays, which are candidates for testing the physics beyond the standard model.

nucl-th↗

arXiv1998

Nuclear moments for the neutrinoless double beta decay

A derivation of the neutrinoless double beta decay rate, specially adapted for the nuclear structure calculations, is presented. It is shown that the Fourier-Bessel expansion of the hadronic currents, jointly with the angular momentum recoupling, leads to very simple final expressions for the nuclear form factors. This greatly facilitates the theoretical estimate of the half life. Our approach does not require the closure approximation, which however can be implemented if desired. The method is exemplified for the $ββ$ decay $^{48}Ca \to ^{48}Ti$, both within the QRPA and a shell-model like model.

hep-ph↗