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Amand Faessler

Publications and source records attributed to Amand Faessler.

At least 145 records · Page 8Linked to original sources
arXiv2006

Hadronic electric dipole moments in R-parity violating supersymmetry

We calculate the electric dipole moments (EDM) of the neutral Hg(199) atom, neutron and deuteron within a generic R-parity violating SUSY model (RPV SUSY) on the basis of a one-pion exchange model with CP-odd pion-nucleon interactions. We consider two types of the RPV SUSY contributions to the above hadronic EDMs: via the quark chromoelectric dipole moments (CEDM) and CP-violating 4-quark interactions. We demonstrate that the former contributes to all the three studied EDMs while the latter appears only in the nuclear EDMs via the CP-odd nuclear forces. We find that the RPV SUSY induced 4-quark interactions arise at tree level through the sneutrino exchange and involve only s and b quarks. Therefore, their effect in hadronic EDMs is determined by the strange and bottom-quark sea of the nucleon. From the null experimental results on the hadronic EDMs we derive the limits on the imaginary parts of certain products Im(lambda'* lambda') of the trilinear RPV-couplings and show that the currently best limits come from the Hg(199) EDM experiments. We demonstrate that some of these limits are better than those existing in the literature. We argue that future storage ring experiments on the deuteron EDM are able to improve these limits by several orders of magnitude.

hep-ph↗
arXiv2006

Strong CP violation and the neutron electric dipole form factor

We calculate the neutron electric dipole form factor induced by the CP violating theta-term of QCD, within a perturbative chiral quark model which includes pion and kaon clouds. On this basis we derive the neutron electric dipole moment and the electron-neutron Schiff moment. From the existing experimental upper limits on the neutron electric dipole moment we extract constraints on the theta-parameter and compare our results with other approaches.

hep-ph↗
arXiv2006

Chiral Dynamics of Baryons in a Lorentz Covariant Quark Model

We develop a manifestly Lorentz covariant chiral quark model for the study of baryons as bound states of constituent quarks dressed by a cloud of pseudoscalar mesons. The approach is based on a non-linear chirally symmetric Lagrangian, which involves effective degrees of freedom - constituent quarks and the chiral (pseudoscalar meson) fields. In a first step, this Lagrangian can be used to perform a dressing of the constituent quarks by a cloud of light pseudoscalar mesons and other heavy states using the calculational technique of infrared dimensional regularization of loop diagrams. We calculate the dressed transition operators with a proper chiral expansion which are relevant for the interaction of quarks with external fields in the presence of a virtual meson cloud. In a second step, these dressed operators are used to calculate baryon matrix elements. Applications are worked out for the masses of the baryon octet, the meson-nucleon sigma terms, the magnetic moments of the baryon octet, the nucleon charge radii, the strong vector meson-nucleon couplings and the full momentum dependence of the electromagnetic form factors of the nucleon.

hep-ph↗
arXiv2006

Transition magnetic moments of Majorana neutrinos in supersymmetry without R-parity in light of neutrino oscillations

The transition magnetic moments of Majorana neutrinos are calculated in grand unified theory (GUT) constrained Minimal Supersymmetric Standard Model (MSSM) with explicit R-parity violation. It is assumed that neutrinos acquire masses via one-loop (quark-squark and lepton-slepton) radiative corrections. The mixing of squarks, sleptons, and quarks is considered explicitly. The connection between neutrino magnetic moments and the entries of neutrino mass matrix is studied. The current upper limits on neutrino magnetic moments are deduced from the elements of phenomenological neutrino mass matrix, which is reconstructed using the neutrino oscillation data and the lower bound on the neutrinoless double beta decay half-life. Further, the results for transitional magnetic moments of Majorana neutrinos are presented for the cases of inverted and normal hierarchy of neutrino masses and different SUSY scenarios. The largest values are of the order of 10^{-17} in units of Bohr magneton.

hep-ph↗
arXiv2006

Magnetic moments of heavy baryons in the relativistic three-quark model

The magnetic moments of ground state single, double and triple heavy baryons containing charm or bottom quarks are calculated in a relativistic three-quark model, which, in the heavy quark limit, is consistent with Heavy Quark Effective Theory and Heavy Hadron Chiral Perturbation Theory. The internal quark structure of baryons is modeled by baryonic three-quark currents with a spin-flavor structure patterned according to standard covariant baryonic wave functions and currents used in QCD sum rule calculations.

hep-ph↗
arXiv2006

Medium effects on phi decays to dilepton and kaon-antikaon pairs in relativistic heavy ion reactions

We consider the role of rescattering of secondary kaons on the dilepton branching ratio of the phi meson. In-medium mass modifications and broadening of kaons and phi mesons are taken into account. We find in the framework of a Bjorken scenario for the time evolution of the expanding fireball that the phi yield from dimuons is moderately or at least only slightly enhanced compared to that from kaon-antikaon pairs. The relation to experimental yields measured by the NA49, NA50 and CERES Collaborations at CERN SPS and the PHENIX Collaboration at RHIC is discussed.

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arXiv2006

$D$-mesons and charmonium states in hot pion matter

We calculate the in-medium $D$ meson self-energies in a hot pion gas induced by resonance interactions with pions. The appropriate resonances in the {\it s},~ {\it p} and {\it d} waves of the $D$ meson-pion pair are represented by low lying scalar, vector and tensor $D^*$ mesons. At temperatures around 200 MeV the D-meson mass drops by $30~ \rm {MeV}$ and the scattering width grows up to $60~ \rm {MeV}$. Similar medium effects are found for the $D^*$ vector mesons. This opens and/or enhances the decay and/or dissociation channels of the charmonium states $Ψ^\prime$, $χ_c$ and $J/Ψ$ to $D \bar D,~D^* \bar D,~D \bar D^* ,~D^* \bar D^*$ pairs in pion matter.

nucl-th↗
arXiv2006

Uncertainties in the $0νββ$--decay nuclear matrix elements

The nuclear matrix elements $M^{0ν}$ of the neutrinoless double beta decay ($0νββ$) of most nuclei with known $2νββ$-decay rates are systematically evaluated using the Quasiparticle Random Phase Approximation (QRPA) and Renormalized QRPA (RQRPA). The experimental $2νββ$-decay rate is used to adjust the most relevant parameter, the strength of the particle-particle interaction. With such procedure the $M^{0ν}$ values become essentially independent on single-particle basis size, the axial vector quenching factor, etc. Theoretical arguments in favor of the adopted way of determining the interaction parameters are presented. It is suggested that most of the spread among the published $M^{0ν}$'s can be ascribed to the choices of implicit and explicit parameters, inherent to the QRPA method.

nucl-th↗
arXiv2006

First application of the continuum-QRPA to description of the double beta decay

A continuum-QRPA approach to calculation of the $2νββ$- and $0νββ$-amplitudes has been formulated. For $^{130}$Te a regular suppression (about 20%) of the high-multipole contributions to the $0νββ$-amplitude has been found which can be associated with additional ground state correlations appearing from the transitions to collective states in the continuum. At the same time the total calculated $0νββ$-amplitude for $^{130}$Te gets suppressed by about 20% as compared to the result of the usual, discretized, QRPA.

nucl-th↗
arXiv2006

The neutron electric dipole form factor in the perturbative chiral quark model

We calculate the electric dipole form factor of the neutron in a perturbative chiral quark model, parameterizing CP-violation of generic origin by means of effective electric dipole moments of the constituent quarks and their CP-violating couplings to the chiral fields. We discuss the relation of these effective parameters to more fundamental ones such as the intrinsic electric and chromoelectric dipole moments of quarks and the Weinberg parameter. From the existing experimental upper limits on the neutron EDM we derive constraints on these CP-violating parameters.

hep-ph↗
arXiv2006

Quantum deformation of the Dirac bracket

The quantum deformation of the Poisson bracket is the Moyal bracket. We construct quantum deformation of the Dirac bracket for systems which admit global symplectic basis for constraint functions. Equivalently, it can be considered as an extension of the Moyal bracket to second-class constraints systems and to gauge-invariant systems which become second class when gauge-fixing conditions are imposed.

hep-th↗
arXiv2006

Quark model description of quasi-elastic pion knockout from the proton at JLAB

The interference term between s- and t-pole contributions to the p(e,e' pi+)n cross section is evaluated on the basis of the constituent quark model. It is shown that the contribution of baryon s-poles can be modeled by a nonlocal extension of the Kroll-Rudermann contact term. This contribution is in a destructive interference with the pion t-pole that is essential to improve the description of recent JLab data at the invariant mass W=1.95 GeV. Some predictions are made for a new JLab measurement at higher values W=2.1-2.3 GeV and Q2 centered at 1.6 and 2.45 GeV2/c2.

hep-ph↗
arXiv2005

Energy densities and equilibration in heavy ion collisions at sqrt(s) = 200 GeV with the quark-gluon string model

We study thermodynamic characteristica of ultra-relativistic Au+Au collisions at RHIC energy sqrt(s) = 200 GeV within the framework of a microscopic transport model, namely the quark-gluon string model (QGSM). The temporal evolution of the local energy density, transverse and longitudinal pressure and equilibration times are considered. In contrast to complete equilibration which is even in central reactions hardly achieved, pre-equilibrium stages with energy densities well above the critical energy density predicted by lattice QCD are established at short time scales. Corresponding energy density profiles at proper time tau = 1 fm/c compare well with hydrodynamical assumptions for initial energy density distributions.

nucl-th↗
arXiv2005

Assessment of uncertainties in QRPA $0νββ$-decay nuclear matrix elements

The nuclear matrix elements $M^{0ν}$ of the neutrinoless double beta decay ($0νββ$) of most nuclei with known $2νββ$-decay rates are systematically evaluated using the Quasiparticle Random Phase Approximation (QRPA) and Renormalized QRPA (RQRPA). The experimental $2νββ$-decay rate is used to adjust the most relevant parameter, the strength of the particle-particle interaction. New results confirm that with such procedure the $M^{0ν}$ values become essentially independent on the size of the single-particle basis. Furthermore, the matrix elements are shown to be also rather stable with respect to the possible quenching of the axial vector strength parametrized by reducing the coupling constant $g_A$, as well as to the uncertainties of parameters describing the short range nucleon correlations. Theoretical arguments in favor of the adopted way of determining the interaction parameters are presented. Furthermore, a discussion of other implicit and explicit parameters, inherent to the QRPA method, is presented. Comparison is made of the ways these factors are chosen by different authors. It is suggested that most of the spread among the published $0νββ$ decay nuclear matrix elements can be ascribed to these choices.

nucl-th↗
arXiv2005

Mass spectrum of the J^P=1/2^- and 3/2^- pentaquark antidecuplets in the perturbative chiral quark model

We study the recently discovered Theta^+ baryon in the context of the perturbative chiral quark model. The basic configuration of the Theta^+ is set up as a pentaquark bound state, where the single particle wave functions are the ground state solutions of a confining potential. We classify the resulting pentaquark multiplets as the J^P=1/2^- and 3/2^- flavor SU(3) antidecuplet. The full mass spectrum of the multiplets is determined by including meson and gluon cloud contributions inducing flavor SU(3) breaking. Mainly due to the semi-perturbative gluon effects the resulting 3/2^- antidecuplet is about 185 MeV heavier than the 1/2^- one. We assign the observed Theta^+ baryon as a member of the 1/2^- antidecuplet and discuss in particular the relation to the recent experimental signal for a Xi^{--} baryon.

hep-ph↗
arXiv2005

Momentum, Density, and Isospin dependence of the Symmetric and Asymmetric Nuclear Matter Properties

Properties of symmetric and asymmetric nuclear matter have been investigated in the relativistic Dirac-Brueckner-Hartree-Fock approach based on projection techniques using the Bonn A potential. The momentum, density, and isospin dependence of the optical potentials and nucleon effective masses are studied. It turns out that the isovector optical potential depends sensitively on density and momentum, but is almost insensitive to the isospin asymmetry. Furthermore, the Dirac mass $m^*_D$ and the nonrelativistic mass $m^*_{NR}$ which parametrizes the energy dependence of the single particle spectrum, are both determined from relativistic Dirac-Brueckner-Hartree-Fock calculations. The nonrelativistic mass shows a characteristic peak structure at momenta slightly above the Fermi momentum $\kf$. The relativistic Dirac mass shows a proton-neutron mass splitting of $m^*_{D,n} m^*_{NR,p}$ which is in agreement with the results from nonrelativistic calculations.

nucl-th↗
arXiv2005

The effects of deformation and pairing correlations on nuclear charge form factor

A set of moderately deformed $s-d$ shell nuclei is employed for testing the reliability of the nuclear ground state wave functions which are obtained in the context of a BCS approach and offer a simultaneous consideration of deformation and pairing correlations effects. In this method, the mean field is assumed to be an axially symmetric Woods-Saxon potential and the effective two-body interaction is a monopole pairing force. As quantities of main interest we have chosen the nuclear form factors, the occupancies of the active (surface) orbits and the Fermi sea depletion, which provide quite good tests for microscopic descriptions of nuclei within many body theories. For our comparisons with results emerging from other similar methods, an axially deformed harmonic oscillator field is also utilized.

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