2,030 research outputs found
Direct Urca processes on nucleons in cooling neutron stars
We use the field theoretical model to perform relativistic calculations of
neutrino energy losses caused by the direct Urca processes on nucleons in the
degenerate baryon matter. By our analysis, the direct neutron decay in the
superdense nuclear matter under beta equilibrium is open only due to the
isovector meson fields, which create a large energy gap between protons and
neutrons in the medium. Our expression for the neutrino energy losses, obtained
in the mean field approximation, incorporates the effects of nucleon recoil,
parity violation, weak magnetism, and pseudoscalar interaction. For numerical
testing of our formula, we use a self-consistent relativistic model of the
multicomponent baryon matter. The relativistic emissivity of the direct Urca
reactions is found substantially larger than predicted in the non-relativistic
approach. We found that, due to weak magnetism effects, relativistic
emissivities increase by approximately 40-50%, while the pseudoscalar
interaction only slightly suppresses the energy losses, approximately by 5%.Comment: 21 pages, 2 figure
Covariant Effective Field Theory for Nuclear Structure and Nuclear Currents
Recent progress in Lorentz-covariant quantum field theories of the nuclear
many-body problem (quantum hadrodynamics or QHD) is discussed. The effective
field theory studied here contains nucleons, pions, isoscalar scalar (\sigma)
and vector (\omega) fields, and isovector vector (\rho) fields. The theory
exhibits a nonlinear realization of spontaneously broken SU(2)_L \times SU(2)_R
chiral symmetry and has three desirable features: it uses the same degrees of
freedom to describe the nuclear currents and the strong-interaction dynamics,
it satisfies the symmetries of the underlying theory of QCD, and its parameters
can be calibrated using strong-interaction phenomena, like hadron scattering or
the empirical properties of finite nuclei. Moreover, it has recently been
verified that for normal nuclear systems, it is possible to expand the
effective Lagrangian systematically in powers of the meson fields (and their
derivatives) and to truncate the expansion reliably after the first few orders.
Using a mean-field version of the energy functional, accurate quantitative
results are obtained for the bulk and single-particle properties of medium- and
heavy-mass nuclei. The importance of modern perspectives in effective field
theory and density functional theory for understanding these successes of QHD
is emphasized. The inclusion of hadronic electromagnetic structure and of
nonanalytic terms in the energy functional is also considered briefly. As a
further application, weak-interaction currents are studied in the QHD
framework. The axial-vector current, evaluated through the leading order in the
field expansion, satisfies both PCAC and the Goldberger--Treiman relation, and
the corresponding vector and axial-vector charges satisfy the familiar chiral
charge algebra to all orders in the pion field.Comment: 32 pages, 9 figures, LaTeX2e with svmult.cls and
svmultphys.clo; invited lecture at 307. WE-Heraeus-Seminar, "Relativistic
Structure Models for the Physics of Radioactive Nuclear Beams," 5/12-16/2003,
Bad Honnef, Germany. Reference list put into correct order; four typos fixe
Role of Hyperon Negative Energy Sea in Nuclear Matter
We have examined the contribution of the filled negative energy sea of
hyperons to the energy/particle in nuclear matter at the one and two loop
levels. While this has the potential to be significant, we find a strong
cancellation between the one and two loop contributions for our chosen
parameters so that hyperon effects can be justifiably neglected.Comment: 12 pages, latex, 1 simple figure attached at end (regular postscript
Representations in Density Dependent Hadronic Field Theory and compatibility with QCD sum-rules
Different representations of an effective, covariant theory of the hadronic
interaction are examined. For this purpose we have introduced nucleon-meson
vertices parametrized in terms of scalar combinations of hadronic fields,
extending the conceptual frame of the Density Dependent Hadronic Field Theory.
Nuclear matter properties at zero temperature are examined in the Mean Field
Approximation, including the equation of state, the Landau parameters, and
collective modes. The treatment of isospin channels in terms of QCD sum rules
inputs is outlined.Comment: 23 pages, 6 PostScript figures, Revtex4 clas
Electroweak Interactions in a Chiral Effective Lagrangian for Nuclei
We have studied electroweak (EW) interactions in quantum hadrodynamics (QHD)
effective field theory (EFT). The Lorentz-covariant EFT contains nucleon, pion,
, isoscalar scalar () and vector () fields, and
isovector vector () fields. The lagrangian exhibits a nonlinear
realization of (approximate) chiral symmetry and
incorporates vector meson dominance. First, we discuss the EW interactions at
the quark level. Then we include EW interactions in QHD EFT by using the
background-field technique. The completed QHD EFT has a nonlinear realization
of (chiral symmetry and baryon number
conservation), as well as realizations of other symmetries including
Lorentz-invariance, , , and . Meanwhile, as we know, chiral symmetry
is manifestly broken due to the nonzero quark masses; the and
symmetries are also broken because of weak interactions. These breaking
patterns are parameterized in a general way in the EFT. Moreover, we have
included the resonance as manifest degrees of freedom in our QHD EFT,
with a discussion of the irrelevance of the well-known pathologies involving
high-spin fields from the modern EFT perspective. This enables us to discuss
physics at the kinematics where the resonance becomes important. As a result,
the effective theory uses hadronic degrees of freedom, satisfies the
constraints due to QCD (symmetries and their breaking pattern), and is
calibrated to strong-interaction phenomena. Applications to (anti)neutrino
scattering are briefly discussed.Comment: 27 pages, 1 figure, intech.cls, submitted to "Quantum Field Theory",
ISBN 979-953-307-392-6. (InTech, Rijeka, Croatia
Can neutrino-induced photon production explain the low energy excess in MiniBooNE?
This report summarizes our study of Neutral Current (NC)-induced photon
production in MiniBooNE, as motivated by the low energy excess in this
experiment [A. A. Aquilar-Arevalo et al. (MiniBooNE Collaboration), Phys. Rev.
Lett. 98, 231801 (2007); 103, 111801 (2009)]. It was proposed that NC photon
production with two anomalous photon- boson-vector meson couplings might
explain the excess. However, our computed event numbers in both neutrino and
antineutrino runs are consistent with the previous MiniBooNE estimate that is
based on their pion production measurement. Various nuclear effects discussed
in our previous works, including nucleon Fermi motion, Pauli blocking, and the
resonance broadening in the nucleus, are taken into account.
Uncertainty due to the two anomalous terms and nuclear effects are studied in a
conservative way.Comment: 7 pages, 4 figures, and 5 tables, typos corrected, references
updated, version for publicatio
- …