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Amand Faessler

Publications and source records attributed to Amand Faessler.

At least 127 records · Page 7Linked to original sources
arXiv2007

Strong and radiative decays of the Ds0*(2317) meson in the DK-molecule picture

We consider a possible interpretation of the new charm-strange meson Ds0*(2317) as a hadronic molecule - a bound state of D and K mesons. Using an effective Lagrangian approach we calculate the strong Ds0* to Ds pi0 and radiative Ds0* to Ds* gamma decays. A new impact related to the DK molecular structure of the Ds0*(2317) meson is that the presence of u(d) quarks in the D and K mesons gives rise to a direct strong isospin-violating transition Ds0* to Ds pi0 in addition to the decay mechanism induced by eta-pi0 mixing considered previously. We show that the direct transition dominates over the eta-pi0 mixing transition in the Ds0* to Ds pi0 decay. Our results for the partial decay widths are consistent with previous calculations.

hep-ph↗
arXiv2007

Ds0*(2317) and Ds1(2460) mesons in two-body B-meson decays

We analyze the branching ratios of B to D(*) + Ds0*(Ds1) decays using the factorization hypothesis. The B to D(*) transition form factors are taken from a model-independent analysis done by Caprini, Lellouch and Neubert based on heavy quark spin symmetry and dispersive constraints, including short-distance and power corrections. The leptonic decay constants fDs0* and fDs1 are calculated assuming a molecular structure for the Ds0* and Ds1 mesons. The calculated branching ratios of B-meson two-body decays are compared with experimental data and other theoretical results.

hep-ph↗
arXiv2007

Semiclassical expansion of quantum characteristics for many-body potential scattering problem

In quantum mechanics, systems can be described in phase space in terms of the Wigner function and the star-product operation. Quantum characteristics, which appear in the Heisenberg picture as the Weyl's symbols of operators of canonical coordinates and momenta, can be used to solve the evolution equations for symbols of other operators acting in the Hilbert space. To any fixed order in the Planck's constant, many-body potential scattering problem simplifies to a statistical-mechanical problem of computing an ensemble of quantum characteristics and their derivatives with respect to the initial canonical coordinates and momenta. The reduction to a system of ordinary differential equations pertains rigorously at any fixed order in $\hbar$. We present semiclassical expansion of quantum characteristics for many-body scattering problem and provide tools for calculation of average values of time-dependent physical observables and cross sections. The method of quantum characteristics admits the consistent incorporation of specific quantum effects, such as non-locality and coherence in propagation of particles, into the semiclassical transport models. We formulate the principle of stationary action for quantum Hamilton's equations and give quantum-mechanical extensions of the Liouville theorem on the conservation of phase-space volume and the Poincaré theorem on the conservation of $2p$ forms. The lowest order quantum corrections to the Kepler periodic orbits are constructed. These corrections show the resonance behavior.

nucl-th↗
arXiv2007

Weyl's symbols of Heisenberg operators of canonical coordinates and momenta as quantum characteristics

The knowledge of quantum phase flow induced under the Weyl's association rule by the evolution of Heisenberg operators of canonical coordinates and momenta allows to find the evolution of symbols of generic Heisenberg operators. The quantum phase flow curves obey the quantum Hamilton's equations and play the role of characteristics. At any fixed level of accuracy of semiclassical expansion, quantum characteristics can be constructed by solving a coupled system of first-order ordinary differential equations for quantum trajectories and generalized Jacobi fields. Classical and quantum constraint systems are discussed. The phase-space analytic geometry based on the star-product operation can hardly be visualized. The statement "quantum trajectory belongs to a constraint submanifold" can be changed e.g. to the opposite by a unitary transformation. Some of relations among quantum objects in phase space are, however, left invariant by unitary transformations and support partly geometric relations of belonging and intersection. Quantum phase flow satisfies the star-composition law and preserves hamiltonian and constraint star-functions.

quant-ph↗
arXiv2007

Charge-exchange reaction cross sections and the Gamow-Teller strength for double beta decay

The proportionality between single charge-exchange reaction cross sections in the forward direction as found, for example from $(p,n)$ and $(^3$He,$t)$ and from $(n,p)$ and $(d,^2$He) reactions, and the Gamow-Teller (GT) strength into the same final nuclear states has been studied and/or assumed often in the past. Using the most physically justified theory we have at our disposal and for the specific example of the ${}^{76}$Ge-${}^{76}$Se system that may undergo double beta-decay, we demonstrate that the proportionality is a relative good assumption for reactions changing a neutron into a proton, i.e. ${}^{76}$Ge$(p,n){}^{76}$As. In this channel, the main contribution to the GT strengths comes from the removal of a neutron from an occupied single-particle (SP) state and putting a proton into an unoccupied SP state having either the same state quantum numbers or those of the spin-orbit partner. In contrast to this, in the second leg of the double beta decay a single proton must be taken from an occupied SP state and a neutron placed in an unoccupied one. This second process often is Pauli forbidden in medium-heavy nuclei and only can be effected if the Fermi surface is smeared out. Such is the case for ${}^{76}$Se$(n,p){}^{76}$As. Our results suggest that one may not always assume a proportionality between the forward-angle cross sections of the charge-exchange reactions and the GT strength in any such medium-heavy nuclei. The discrepancy originates from a pronounced effect of the radial dependence of the nucleon-nucleon ($NN$) interaction in connection with the Pauli principle on the cross sections in the $(n,p)$ reaction channel. Such a radial dependence is completely absent in the GT transition operator.

nucl-th↗
arXiv2007

On the possible resolution of the B-meson decay polarization anomaly in R-parity violating SUSY

We examine the possible resolution of the recently observed polarization anomaly in B0(bar{B}0) -> phi K*0(bar{K}*0) decay within R-parity violating (RPV) SUSY. We show that a combination of the superpotential trilinear (RPV)-interactions, with the couplings lambda', and the soft SUSY breaking bilinear RPV, sneutrino-Higgs mixing, proportional to tilde{mu}**2, can potentially generate the effective operators with the chirality structure necessary to account for this anomaly. However, we demonstrate that the existing experimental data on Bs -> mu+ mu- decay lead to stringent upper limits on the Wilson coefficients of these operators, which are about two orders of magnitude below the values required for the resolution of the B-decay polarization anomaly, and, therefore, it can hardly be explained within the RPV SUSY framework. As a byproduct result of our analysis we derive new limits on the products of the soft bilinear and the superpotential trilinear RPV-parameters of the form tilde{mu}**2 * lambda'.

hep-ph↗
arXiv2007

Ward-Takahashi identity, soft photon theorem and the magnetic moment of the $Δ$ resonance

Starting from the Ward-Takahashi identity for the radiative $πN$ scattering amplitude a generalization of the soft photon theorem approach is obtained for an arbitrary energy of an emitted photon. The external particle radiation part of the $πN\toγ'π'N' $ amplitude is analytically reduced to the double $Δ$ exchange amplitude with the $Δ\toγ'Δ'$ vertex function. We have shown, that the double $Δ$ exchange amplitudes with internal $Δ$ radiation is connected by current conservation with the corresponding part of the external particle radiation terms. Moreover according to the current conservation the internal and external particle radiation terms with the $Δ-γ'Δ'$ vertex have a opposite sign i.e. they must cancel each other. Therefore we have a screening of the internal double $Δ$ exchange diagram with the $Δ-γ' Δ'$ vertex by the external particle radiation. This enables us to obtain a model independent estimation of the dipole magnetic moment of $Δ^+$ and $Δ^{++}$ resonances $μ_Δ$ through the anomalous magnetic moment of the proton $μ_p$ as $μ_{Δ^+}={{M_Δ}\over {m_p}} μ_p$ and $μ_{Δ^{++}}={3\over 2}μ_{Δ^+}$ in agreement with the values obtained from the fit of the experimental cross section of the $π^+ p\toγ'π^+ p$ reaction.

nucl-th↗
arXiv2006

Dirac-Brueckner-Hartree-Fock calculations for isospin asymmetric nuclear matter based on improved approximation schemes

We present Dirac-Brueckner-Hartree-Fock calculations for isospin asymmetric nuclear matter which are based on improved approximations schemes. The potential matrix elements have been adapted for isospin asymmetric nuclear matter in order to account for the proton-neutron mass splitting in a more consistent way. The proton properties are particularly sensitive to this adaption and its consequences, whereas the neutron properties remains almost unaffected in neutron rich matter. Although at present full Brueckner calculations are still too complex to apply to finite nuclei, these relativistic Brueckner results can be used as a guidance to construct a density dependent relativistic mean field theory, which can be applied to finite nuclei. It is found that an accurate reproduction of the Dirac-Brueckner-Hartree-Fock equation of state requires a renormalization of these coupling functions.

nucl-th↗
arXiv2006

Direct Wimp Detection in Directional Experiments

The recent WMAP data have confirmed that exotic dark matter together with the vacuum energy (cosmological constant) dominate in the flat Universe. Thus the direct dark matter search, consisting of detecting the recoiling nucleus, is central to particle physics and cosmology. Modern particle theories naturally provide viable cold dark matter candidates with masses in the GeV-TeV region. Supersymmetry provides the lightest supersymmetric particle (LSP), theories in extra dimensions the lightest Kaluza-Klein particle (LKP) etc. In such theories the expected rates are much lower than the present experimental goals. So one should exploit characteristic signatures of the reaction, such as the modulation effect and, in directional experiments, the correlation of the event rates with the sun's motion. In standard non directional experiments the modulation is small, less than two per cent and the location of the maximum depends on the unknown particle's mass. In directional experiments, in addition to the forward-backward asymmetry due to the sun's motion, one expects a larger modulation, which depends on the direction of observation. We study such effects both in the case of a light and a heavy target. Furthermore, since it now appears that the planned experiments will be partly directional, in the sense that they can only detect the line of the recoiling nucleus, but not the sense of direction on it, we study which of the above mentioned interesting features, if any, will persist in these less ambitious experiments.

hep-ph↗
arXiv2006

Density resummation of perturbation series in a pion gas to leading order in chiral perturbation theory

The mean field (MF) approximation for the pion matter, being equivalent to the leading ChPT order, involves no dynamical loops and, if self-consistent, produces finite renormalizations only. The weight factor of the Haar measure of the pion fields, entering the path integral, generates an effective Lagrangian $δ\mathcal{L}_{H}$ which is generally singular in the continuum limit. There exists one parameterization of the pion fields only, for which the weight factor is equal to unity and $δ\mathcal{L}_{H}=0$, respectively. This unique parameterization ensures selfconsistency of the MF approximation. We use it to calculate thermal Green functions of the pion gas in the MF approximation as a power series over the temperature. The Borel transforms of thermal averages of a function $\mathcal{J}(χ^αχ^α)$ of the pion fields $χ^α$ with respect to the scalar pion density are found to be $\frac{2}{\sqrtπ}\mathcal{J}(4t)$. The perturbation series over the scalar pion density for basic characteristics of the pion matter such as the pion propagator, the pion optical potential, the scalar quark condensate $<{\bar{q}}q>$, the in-medium pion decay constant ${\tilde{F}}$, and the equation of state of pion matter appear to be asymptotic ones. These series are summed up using the contour-improved Borel resummation method. The quark scalar condensate decreases smoothly until $T_{max}\simeq 310$ MeV. The temperature $T_{max}$ is the maximum temperature admissible for thermalized non-linear sigma model at zero pion chemical potentials. The estimate of $T_{max}$ is above the chemical freeze-out temperature $T\simeq 170$ MeV at RHIC and above the phase transition to two-flavor quark matter $T_{c} \simeq 175$ MeV, predicted by lattice gauge theories.

hep-ph↗
arXiv2006

Implications of R-parity violating supersymmetry for atomic and hadronic EDMs

We calculate the electric dipole moments (EDM) of the neutral Hg(199) atom, deuteron, nucleons and neutral hyperons Lambda, Sigma(0) and Xi(0) in the framework of a generic SUSY model without R-parity conservation (RPV SUSY) on the basis of the SU(3) version of chiral perturbation theory (ChPT). We consider CP-violation in the hadronic sector induced by the chromoelectric quark dipole moments and CP-violating 4-quark effective interactions. From the null experimental results on the neutron and Hg(199) atom EDMs we derive limits on the imaginary parts of certain products Im(lambda' lambda'*) of the trilinear RPV-couplings and demonstrate that they are more stringent than those existing in the literature. Using these limits we give predictions for the EDMs of neutral hyperons. We also estimate the prospects of future storage ring experiments on the deuteron EDM and show that the expected improvement of the above limits in these experiments may reach several orders of magnitude.

hep-ph↗
arXiv2006

Direct Detection Rates of Dark Matter Coupled to Dark Energy

We investigate the effect of a coupling between dark matter and dark energy on the rates for the direct detection of dark matter. The magnitude of the effect depends on the strength $κ$ of this new interaction relative to gravity. The resulting isothermal velocity distribution for dark matter in galaxy halos is still Maxwell-Boltzmann (M-B), but the characteristic velocity and the escape velocity are increased by $\sqrt{1+κ^2}$. We adopt a phenomenological approach and consider values of $κ$ near unity. For such values we find that: (i) The (time averaged) event rate increases for light WIMPs, while it is somewhat reduced for WIMP masses larger than 100 GeV. (ii) The time dependence of the rate arising from the modulation amplitude is decreased compared to the standard M-B velocity distribution. (iii) The average and maximum WIMP energy increase proportionally to $1+κ^2$, which, for sufficiently massive WIMPs, allows the possibility of designing experiments measuring $γ$ rays following nuclear de-excitation.

hep-ph↗
arXiv2006

Solvable models for the gamma deformation having X(5) as limiting symmetry. Removing some drawbacks of the existent descriptions

Two solvable Hamiltonians for describing the dynamic gamma deformation, are proposed. The limiting case of each of them is the X(5) Hamiltonian. Analytical solutions for both energies and wave functions, which are periodic in $γ$, are presented in terms of spheroidal and Mathieu functions, respectively. Moreover, the gamma depending factors of the transition operator can be treated.

nucl-th↗
arXiv2006

Underlying gauge symmetries of second-class constraints systems

Gauge-invariant systems in unconstrained configuration and phase spaces, equivalent to second-class constraints systems upon a gauge-fixing, are discussed. A mathematical pendulum on an $n-1$-dimensional sphere $S^{n-1}$ as an example of a mechanical second-class constraints system and the O(n) non-linear sigma model as an example of a field theory under second-class constraints are discussed in details and quantized using the existence of underlying dilatation gauge symmetry and by solving the constraint equations explicitly. The underlying gauge symmetries involve, in general, velocity dependent gauge transformations and new auxiliary variables in extended configuration space. Systems under second-class holonomic constraints have gauge-invariant counterparts within original configuration and phase spaces. The Dirac's supplementary conditions for wave functions of first-class constraints systems are formulated in terms of the Wigner functions which admit, as we show, a broad set of physically equivalent supplementary conditions. Their concrete form depends on the manner the Wigner functions are extrapolated from the constraint submanifolds into the whole phase space.

hep-th↗
arXiv2006

Isoscalar short-range current in the deuteron induced by an intermediate dibaryon

A new model for short-range isoscalar currents in the deuteron and in the NN system is developed; it is based on the generation of an intermediate dibaryon which is the basic ingredient for the medium- and short-range NN interaction which was proposed recently by the present authors.This new current model can very well describe the experimental data for the three basic deuteron observables of isoscalar magnetic type, viz. the magnetic moment, the circular polarization of the photon in the $np\to dγ$ process at thermal neutron energies and the structure function B up to Q$^2$=60 fm$^{-2}$.

nucl-th↗