200 research outputs found
Neutron-Proton Mass Difference in Nuclear Matter and in Finite Nuclei and the Nolen-Schiffer Anomaly
The neutron-proton mass difference in (isospin asymmetric) nuclear matter and
finite nuclei is studied in the framework of a medium-modified Skyrme model.
The proposed effective Lagrangian incorporates both the medium influence of the
surrounding nuclear environment on the single nucleon properties and an
explicit isospin-breaking effect in the mesonic sector. Energy-dependent
charged and neutral pion optical potentials in the s- and p-wave channels are
included as well. The present approach predicts that the neutron-proton mass
difference is mainly dictated by its strong part and that it markedly decreases
in neutron matter. Furthermore, the possible interplay between the effective
nucleon mass in finite nuclei and the Nolen-Schiffer anomaly is discussed. In
particular, we find that a correct description of the properties of mirror
nuclei leads to a stringent restriction of possible modifications of the
nucleon's effective mass in nuclei.Comment: 10 pages, 8 figures, presentation at the 19th Int. IUPAP Conf. on
Few-Body Problems in Physics (Aug.31-Sep.5, 2009, Univ.of Bonn, Germany
The nucleon-nucleon interaction and properties of the nucleon in a soliton model including a dilaton field with anomalous dimension
We investigate an extended chiral soliton model which includes and mesons as explicit degrees of freedom. The Lagrangian
incorporates chiral symmetry and broken scale invariance. A scalar-isoscalar
meson is associated with a quarkonium dilaton field with a mass
\msig\approx 550 MeV. We show that the scalar field with anomalous dimension
slightly changes the static and electromagnetic properties of the nucleon. In
contrast, it plays a significant role in nucleon-nucleon dynamics and gives an
opportunity to describe well the two-nucleon interaction.Comment: 14 pages, REVTeX, 3 figures (Ps), 83 k
Wave packet dynamics and valley filter in strained graphene
The time evolution of a wavepacket in strained graphene is studied within the
tight-binding model and continuum model. The effect of an external magnetic
field, as well as a strain-induced pseudo-magnetic field, on the wave packet
trajectories and zitterbewegung are analyzed. Combining the effects of strain
with those of an external magnetic field produces an effective magnetic field
which is large in one of the Dirac cones, but can be practically zero in the
other. We construct an efficient valley filter, where for a propagating
incoming wave packet consisting of momenta around the K and K' Dirac points,
the outgoing wave packet exhibits momenta in only one of these Dirac points,
while the components of the packet that belong to the other Dirac point are
reflected due to the Lorentz force. We also found that the zitterbewegung is
permanent in time in the presence of either external or strain-induced magnetic
fields, but when both the external and strain-induced magnetic fields are
present, the zitterbewegung is transient in one of the Dirac cones, whereas in
the other cone the wave packet exhibits permanent spatial oscillations.Comment: 13 pages, 10 figure
Formation of ions by high energy photons
We calculate the electron energy spectrum of ionization by a high energy
photon, accompanied by creation of electron-positron pair. The total cross
section of the process is also obtained. The asymptotics of the cross section
does not depend on the photon energies. At the photon energies exceeding a
certain value this appeares to to be the dominant mechanism of
formation of the ions. The dependence of on the value of nuclear
charge is obtained. Our results are consistent with experimental data.Comment: 16 pages, 6 figure
Meson - nucleon vertex form factors at finite temperature
In this paper the dependence of meson-nucleon-nucleon vertex form factors is
studied as a function of termperature. The results are obtained starting from a
zero temperature Bonn potential. The temperature dependence of the vertex form
factors and radii is studied in the thermofield dynamics, a real-time operator
formalism of finite temperature field theory. It is anticipated that these
results will have an impact on the study of relativistic heavy-ion collisions
as the critical temperature for the phase transition from hadronic to
quark-gluon system is approached.Comment: 19 pages, Revtex, 11 figures (Ps), 171k
Nucleon deformation in finite nuclei
The deformation of a nucleon embedded in various finite nuclei is considered
by taking into account the distortion of the chiral profile functions under the
action of an external field representing the nuclear density. The baryon charge
distribution of the nucleon inside light, medium-heavy and heavy nuclei is
discussed. The mass of the nucleon decreases as it is placed deeper inside the
nucleus and reaches its minimum at the center of the nucleus. We discuss the
quantization of non-spherical solitons and its consequences for the mass
splitting of the delta states. We show that bound nucleons acquire an intrinsic
quadrupole moment due to the deformation effects. These effects are maximal for
densities of nuclei about \rho(R)\sim 0.3...0.35 \rho(0). We also point out
that scale changes of the electromagnetic radii can not simply be described by
an overall swelling factor.Comment: 29 pp, REVTeX, 8 figures, more detailed discussion on quantization
and intrinsic quadrupole moments, references adde
Neutron-proton mass difference in nuclear matter
Isospin-breaking effects in nuclear matter are studied in the framework of a
medium-modified Skyrme model. The proposed effective Lagrangian incorporates
both the medium influence of the surrounding nuclear environment on the single
nucleon properties and an explicit isospin-breaking effect in the mesonic
sector. The approach predicts that the neutron-proton mass difference decreases
in isospin-symmetric nuclear matter but by a very small amount only.Comment: 8 pages, 4 figures, revised versio
Finite temperature amplitudes and reaction rates in Thermofield dynamics
We propose a method for calculating the reaction rates and transition
amplitudes of generic process taking place in a many body system in
equilibrium. The relationship of the scattering and decay amplitudes as
calculated in Thermo Field Dynamics the conventional techniques is established.
It is shown that in many cases the calculations are relatively easy in TFD.Comment: 32 pages, RevTex, 2 PS figures, to appear in Phys. Rev.
Evaluation of heat losses of the solar greenhouse during the heating season
The article presents the results of calculation of heat losses in greenhouses with different coatings, taking into account thermal-physical properties of coatings. In addition, based on the results of changes in external air temperature and solar radiation over time, numerical calculations were made on the heat load of a greenhouse with a useful area of 108 m2 and the thermal power provided by solar energy
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