262 research outputs found
Sterile neutrinos in neutrinoless double beta decay
We study possible contribution of the Majorana neutrino mass eigenstate
dominated by a sterile neutrino component to neutrinoless double beta
() decay. From the current experimental lower bound on the
-decay half-life of Ge we derive stringent constraints
on the mixing in a wide region of the values of mass. We
discuss cosmological and astrophysical status of in this mass region.Comment: 6 pages, 1 figure; v2 added comments and reference
Robust optical emission polarization in MoS2 monolayers through selective valley excitation
We report polarization resolved photoluminescence from monolayer MoS2, a
two-dimensional, non-centrosymmetric crystal with direct energy gaps at two
different valleys in momentum space. The inherent chiral optical selectivity
allows exciting one of these valleys and close to 90% polarized emission at 4K
is observed with 40% polarization remaining at 300K. The high polarization
degree of the emission remains unchanged in transverse magnetic fields up to 9T
indicating robust, selective valley excitation.Comment: 5 pages, 3 figure
Role of the rho meson in the description of pion electroproduction experiments at JLab
We study the p(e,e' pi+)n reaction in the framework of an effective
Lagrangian approach including nucleon, pi and rho meson degrees of freedom and
show the importance of the rho-meson t-pole contribution to sigmaT, the
transverse part of cross section. We test two different field representations
of the rho meson, vector and tensor, and find that the tensor representation of
the rho meson is more reliable in the description of the existing data. In
particular, we show that the rho-meson t-pole contribution, including the
interference with an effective non-local contact term, sufficiently improves
the description of the recent JLab data at invariant mass W less 2.2 GeV and Q2
less 2.5 GeV2/c2. A ``soft'' variant of the strong piNN and rhoNN form factors
is also found to be compatible with these data. On the basis of the successful
description of both the sigmaL and sigmaT parts of the cross section we discuss
the importance of taking into account the sigmaT data when extracting the
charge pion form factor Fpi from sigmaL.Comment: 23 pages, 6 figures, accepted for publication in Phys. Rev.
Anisotropic flow of charged and identified hadrons in the quark-gluon string model for Au+Au collisions at sqrt(s) = 200 GeV
The pseudorapidity behaviour of the azimuthal anisotropy parameters v_1 and
v_2 of inclusive charged hadrons and their dependence on the centrality has
been studied in Au+Au collisions at full RHIC energy of sqrt(s) = 200 GeV
within the microscopic quark-gluon string model. The QGSM simulation results
for the directed flow v_1 show antiflow alignment within the pseudorapidity
range |eta| < 2 in a fair agreement with the experimental v_1(eta) data, but
cannot reproduce the further development of the antiflow up to |eta| around
3.5. The eta dependence of the elliptic flow v_2 extracted from the simulations
agrees well with the experimental data in the whole pseudorapidity range for
different centrality classes. The centrality dependence of the integrated
elliptic flow of charged hadrons in the QGSM almost coincides with the PHOBOS
experimental distribution. The transverse momentum dependence of the elliptic
flow of identified and inclusive charged hadrons is studied also. The model
reproduces quantitatively the low p_T part of the distributions rather good,
but underestimates the measured elliptic flow for transverse momenta p_T > 1
GeV/c. Qualitatively, however, the model is able to reproduce the saturation of
the v_2(p_T) spectra with rising p_T as well as the crossing of the elliptic
flow for mesons and baryons.Comment: REVTeX, 10 pages, 10 figures, v2: extended discussion of the model
results, accepted for publication in Phys. Rev.
New features of the triaxial nuclei described with a coherent state model
Supplementing the Liquid Drop Model (LDM) Hamiltonian, written in the
intrinsic reference frame, with a sextic oscillator plus a centrifugal term in
the variable and a potential in with a minimum in
, the Sch\"{o}dinger equation is separated for the two variables
which results in having a new description for the triaxial nuclei, called
Sextic and Mathieu Approach (SMA). SMA is applied for two non-axial nuclei,
Hf and W and results are compared with those yielded by the
Coherent State Model (CSM). As the main result of this paper we derive
analytically the equations characterizing SMA from a semi-classical treatment
of the CSM Hamiltonian. In this manner the potentials in and
variables respectively, show up in a quite natural way which contrasts their
ad-hoc choice when SMA emerges from LDM.Comment: 13 figures, 13 page
Proton-neutron pairing in the deformed BCS approach
We examine isovector and isoscalar proton-neutron pairing correlations for
the ground state of even-even Ge isotopes with mass number A=64-76 within the
deformed BCS approach. For N=Z 64Ge the BCS solution with only T=0
proton-neutron pairs is found. For other nuclear systems (N>Z) a coexistence of
a T=0 and T=1 pairs in the BCS wave function is observed. A problem of fixing
of strengths of isoscalar and isovector pairing interactions is addressed. A
dependence of number of like and unlike pairs in the BCS ground state on the
difference between number of neutrons and protons is discussed. We found that
for nuclei with N much bigger than Z the effect of proton-neutron pairing is
small but not negligible.Comment: 24 pages, 6 figure
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.Comment: 27 pages REVTeX, 6 EPS Figures. New references added. Accepted for
publication to JM
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