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A. Hosaka

Publications and source records attributed to A. Hosaka.

At least 55 records · Page 3Linked to original sources
arXiv2011

Vector meson-Baryon dynamics and generation of resonances

The purpose of this work is to study vector meson-octet baryon interactions with the aim to find dynamical generation of resonances in such systems. For this, we consider s-, t-, u-channel diagrams along with a contact interaction originating from the hidden local symmetry Lagrangian. We find the contribution from all these sources, except the s-channel, to be important. The amplitudes obtained by solving coupled channel Bethe Salpeter equations for systems with total strangeness zero, show generation of one isospin 3/2, spin 1/2 resonance and three isospin 1/2 resonances: two with spin 3/2 and one with spin 1/2. We identify these resonances with $Δ(1900) S_{31}$, $N^* (2080) D_{13}$, $N^* (1700) D_{13}$, and $N^*(2090) S_{11}$, respectively.

hep-ph↗
arXiv2010

Neutrino pair emission off electrons in a strong electromagnetic wave field

The emission of $ν\barν$ pairs off electrons in a polarized ultra-intense electromagnetic (e.g.\ laser) wave field is analyzed. We elaborate on the significance of non-linear electrodynamics effects (i.e., multi-photon processes) and the peculiarities of neutrino production. Special attention is devoted to the convergence of the reaction probabilities as a function of the number of absorbed photons. Expressions for large field intensities are provided. The asymmetry between the probabilities of electron and $μ+τ$ neutrino production depends on initial conditions such as energy of the wave field photons and the field intensity. These findings differ from the lowest order perturbative calculation of the reaction $γ+ e \to e' + ν\bar ν$.

hep-ph↗
arXiv2010

Scalar, axial-vector and tensor resonances from the $ρD^*$, $ωD^*$ interaction in the hidden gauge formalism

We apply a unitary approach together with a set of hidden-gauge Lagrangians to study the vector-vector interaction. We study the case of the $ρ$($ω$)$D^*$ interaction within the model. In $I=1/2$ we get strong enough attraction to bind the system. Concretely, we get one resonance for each spin $J=0,1,2$. For J=1 and 2 these resonances can be easily identified with the $D^*(2460)$ and $D^*(2640)$. Whereas the state for J=0 with mass $M\sim2600$ MeV is a prediction of the model. In $I=3/2$ we get a repulsive interaction and hence no exotic dynamically generated states.

hep-ph↗
arXiv2009

A Lagrangian for the Chiral (1/2,0) + (0,1/2) Quartet Nucleon Resonances

We study the nucleon and three N* resonances' properties in an effective linear realization chiral SU_L(2) x SU_R(2) and U_A(1) symmetric Lagrangian. We place the nucleon fields into the so-called "naive" (1/2,0) + (0, 1/2) and "mirror" (0, 1/2) + (1/2,0) (fundamental) representations of SU_L(2) x SU_R(2), two of each -distinguished by their U_A(1) chiral properties, as defined by an explicit construction of the nucleon interpolating fields in terms of three quark (Dirac) fields. We construct the most general one-meson-baryon chiral interaction Lagrangian assuming various parities of these four nucleon fields. We show that the observed masses of the four lowest lying nucleon states can be well reproduced with the effective Lagrangian, after spontaneous symmetry breakdown, without explicit breaking of U_A(1) symmetry. This does not mean that explicit U_A(1) symmetry breaking does not occur in baryons, but rather that it does not have a unique mass prediction signature that exists e.g. in the case of spinless mesons. We also consider briefly the axial couplings with chiral representation mixing.

hep-ph↗
arXiv2009

Nucleon axial couplings and [(1/2,0) + (0,1/2)]-[(1,1/2) + (1/2,1)] chiral multiplet mixing

Three-quark nucleon interpolating fields in QCD have well-defined SU_L(2) x SU_R(2) and U_A(1) chiral transformation properties. Mixing of the [(1,1/2) + (1/2,1)] chiral multiplet with one of [(1/2,0) + (0,1/2)] or [(0,1/2) + (1/2,0)] representation can be used to fit the isovector axial coupling g_A(1) and thus predict the isoscalar axial coupling g_A(0) of the nucleon, in reasonable agreement with experiment. We also use a chiral meson-baryon interaction to calculate the masses and one-pion-interaction terms of J=1/2 baryons belonging to the [(0,1/2) + (1/2,0)] and [(1,1/2) + (1/2,1)] chiral multiplets and fit two of the diagonalized masses to the lowest-lying nucleon resonances thus predicting the third J=1/2 resonance at 2030 MeV, not far from the (one-star PDG) state Delta(2150).

hep-ph↗
arXiv2009

Charged K* Photoproduction in a Regge model

We investigate $γp \to K^{*+} Λ$ reaction within a Regge approach. For the gauge invariance of the scattering amplitude, we reggeize the s-channel and contact term amplitudes as well as the $t$-channel amplitude. We obtain the decreasing behavior of the total cross section as the CLAS's preliminary data show. We also calculate spin density matrices, and find clear differences between our Regge model and the previous Feynman (isobar) model.

hep-ph↗
arXiv2009

A coupled-channel analysis for phi-photoproduction with Lambda(1520)

We investigate photoproduction of $ϕ$-mesons off protons within a coupled-channel effective-Lagrangian method which is based on the K-matrix approach. Since the threshold energy of the $KΛ(1520)$ channel is close to that of $ϕN$, the contribution of this channel to $ϕ$-photoproduction near the threshold energy region may give rise to some unexpected structures. In the transition amplitude $KΛ(1520) \to ϕN$, the kinematics allows an intermediate kaon to be on-shell. This happens in the energy region where a peak structure has been observed in $ϕ$-photoproduction. In our calculations the on-shell kaon effect indeed reproduces a peak structure, however, with a magnitude that is far too small to explain the observed effect. As a following step we introduce a nucleon resonance in our model. The coupling of the resonance to the $KΛ(1520)$ and $ϕN$ channels is not suppressed by the OZI rule if the resonance contains a dominant hidden strangeness component. We find that the resonance can reproduce a peak structure of the correct magnitude at the right energy. We also investigate the effects of coupled channels and the resonance on the angular distribution and the spin density matrices for $ϕ$ photoproduction.

hep-ph↗
arXiv2009

Scalar, axial-vector and tensor resonances from the rho D^*, omega D^* interaction in the hidden gauge formalism

We study composite systems of light ($ρ$ and $ω$) and heavy ($D^*$) vector mesons by using the interaction within the hidden gauge formalism. We find a strong attraction in the isospin, spin channels $(I,S)=(1/2,0)$; $(1/2,1)$; $(1/2,2)$ with positive parity. The attraction is large enough to strongly bind these mesons in states with these quantum numbers, leading to states which can be identified with $D_2^*(2460)$ and probably with $D^*(2640)$, the last one without experimental spin and parity assignment. In the case of $I=3/2$ one obtains repulsion and thus, no exotic mesons in this sector are generated in the approach.

hep-ph↗
arXiv2008

Hidden gauge formalism for the radiative decays of axial-vector mesons

The radiative decay of the axial-vector resonances into a pseudoscalar meson and a photon is studied using the vector meson Lagrangian obtained from the hidden gauge symmetry (HGS) formalism. The formalism is well suited to study this problem since it deals with pseudoscalar and vector mesons in a unified way, respecting chiral invariance. We show explicitly the gauge invariance of the set of diagrams that appear in the approach and evaluate the radiative decay width of the a1(1260) and b1(1235) axial vector meson resonances into pi gamma. We also include the contribution of loops involving anomalous couplings and compare the results to those obtained previously within another formalism.

hep-ph↗
arXiv2008

$πN$ and $ππN$ Couplings of the $Δ(1232)$ and its Chiral Partners

We investigate the interactions and chiral properties of the four spin-$\thalf$-baryons : $N^-(D_{13})$, $N^+(P_{13})$, $Δ^+(P_{33})$ and $Δ^-(D_{33})$ together with the nucleon. We construct the $SU(2)_R \times SU(2)_L$ invariant interactions between the spin-$\half$ and -$\thalf$ baryons with the aid of a new, specially developed spin and isospin projection technique for these baryon fields, where the chiral invariant interactions contain one- and two-pion couplings. We obtain simple relations for the coupling constants of the one- and two-pion spin $\half-\thalf$ transitions terms. The relation for the one-pion interactions reasonably agrees with the experiments, which suggests that these spin-$\thalf$ baryons are chiral partners.

hep-ph↗
arXiv2007

Magnetic interaction induced by the anomaly in kaon-photoproductions

We study the role of magnetic interaction in the photoproduction of the kaon and hyperon. We find that the inclusion of a higher order diagram induced by the Wess-Zumio-Witten term has a significant contribution to the magnetic amplitude, which is compatible to the observed photon asymmetry in the forward angle region. This enables us to use the K^* coupling constants which have been determined in a microscopic way rather than the phenomenological ones which differ largely from the microscopic ones.

hep-ph↗
arXiv2007

Quantum loops in radiative decays of the $a_1$ and $b_1$ axial-vector mesons

A previous model where the low-lying axial-vector mesons are dynamically generated, implementing unitarity in coupled channels in the vector-pseudoscalar ($VP$) meson interaction, is applied to evaluate the decay widths of the a_1(1260)$ and $b_1(1235)$ axial-vector mesons into $πγ$. Unlike the case of the $a_1$, the $b_1$ radiative decay is systematically underestimated at tree level. In this work we evaluate for the first time the loop contribution coming from an initial $VP$ vertex. Despite the large superficial divergence of the loops, the convergence of the relevant loops can be established by using arguments of gauge invariance. The partial decay widths obtained agree very well with the experimental values within uncertainties, and show that the loop contribution is crucial in the $b_1$ case and also important for the $a_1$ case.

hep-ph↗
arXiv2007

Quark condensates in the chiral bag with the NJL interaction

We discuss the quark condensate of the vacuum inside the baryon. We analyze the 1+1 dimensional chiral bag in analogy with the realistic 3+1 dimensional one. The Nambu--Jona-Lasinio (NJL) type interaction is used to investigate the quark condensate in the chiral bag. Considering the strong meson-quark coupling, we solve the mean field solution to the scalar and pseudoscalar channels by including the chiral Casimir effects. The self-consistent equation allows a finite value of the quark condensate and hence a finite dynamical quark mass inside the bag. It is shown that an approximate Cheshire Cat picture holds for massive quarks.

hep-ph↗
arXiv2007

Effect of negative energy components for two-nucleon systems in the relativistic framework with the separable ansatz

We investigate the electromagnetic properties of the deuteron such as the charge and magnetic form factors by solving the Bethe-Salpeter equation (BSE) with the separable ansatz. In solving the deuteron bound state solution to the BSE, we include negative energy components of $P$-wave in addition to the $^3S_1$ and $^3D_1$ states of positive energy, employing a rank IV separable ansatz. We found that the inclusion of the negative energy components improves systematically the electromagnetic properties which are not described in the conventional non-relativistic impulse approximation.

nucl-th↗
arXiv2006

Quark droplets with chiral symmetry in the Nambu--Jona-Lasinio model

We discuss the stability of strangelets by considering dynamical chiral symmetry breaking. For quark droplets of finite volume, we formulate the Nambu--Jona-Lasinio model with a basis set of the quark wave functions in the chiral bag model. Chiral symmetry breaking for the finite volume bag is discussed in a mean field approximation. Effects of the pion cloud including the chiral Casimir effect are investigated. Physical quantities of the quark droplets such as masses and radii are obtained for quark droplets of baryon numbers up to five. We also apply our model setting to the nucleon and discuss the stability of the quark droplets against nuclei.

hep-ph↗
arXiv2006

Chiral symmetry breaking and stability of quark droplets

We discuss the stability of strangelets -- quark droplets with strangeness -- in the Nambu--Jona-Lasinio model supplemented by a boundary condition for quark confinement. Effects of dynamical chiral symmetry breaking are considered properly inside quark droplets of arbitrary baryon number. We obtain the energy per baryon number of quark droplets with baryon number from one to thousands. It is shown that strangelets are not the ground states as compared with nuclei, though they can be locally stable.

hep-ph↗