39 research outputs found
Renormalization of the Spin-dependent WIMP scattering off nuclei
We study the amplitude for the spin-dependent WIMP scattering off nuclei by
including the leading long-range two-body currents in the most important
isovector contribution. We show that such effects are essentially independent
of the target nucleus and, as a result, they can be treated as a mere
renormalization of the effective nucleon cross section or, equivalently, of the
corresponding effective coupling with values around 25%.Comment: 15 pages, 4 figures, 2 tables. arXiv admin note: text overlap with
arXiv:1211.321
Cross Sections of Charged Current Neutrino Scattering off 132
The total cross sections as well as the neutrino event rates are calculated in the charged current neutrino and antineutrino scattering off 132Xe isotope at neutrino energies Ev<100 MeV. Transitions to excited nuclear states are calculated in the framework of quasiparticle random-phase approximation. The contributions from different multipoles are shown for various neutrino energies. Flux-averaged cross sections are obtained by convolving the cross sections with a two-parameter Fermi-Dirac distribution. The flux-averaged cross sections are also calculated using terrestrial neutrino sources based on conventional sources (muon decay at rest) or on low-energy beta-beams
Coherent and Incoherent Neutral Current Scattering for Supernova Detection
The total cross sections as well as the neutrino event rates are calculated in the neutral current neutrino scattering off 40Ar and 132Xe isotopes at neutrino energies (Ev<100 MeV). The individual contribution coming from coherent and incoherent channels is taking into account. An enhancement of the neutral current component is achieved via the coherent (0gs+→0gs+) channel which is dominant with respect to incoherent (0gs+→Jf) one. The response of the above isotopes as a supernova neutrino detection has been considered, assuming a two parameter Fermi-Dirac distribution for the supernova neutrino energy spectra. The calculated total cross sections are tested on a gaseous spherical TPC detector dedicated for supernova neutrino detection
Beats of the Magnetocapacitance Oscillations in Lateral Semiconductor Superlattices
We present calculations on the magnetocapacitance of the two-dimensional
electron gas in a lateral semiconductor superlattice under two-dimensional weak
periodic potential modulation in the presence of a perpendicular magnetic
field. Adopting a Gaussian broadening of magnetic-field-dependent width in the
density of states, we present explicit and simple expressions for the
magnetocapacitance, valid for the relevant weak magnetic fields and modulation
strengths. As the modulation strength in both directions increase, beats of the
magnetocapacitance oscillations are observed, in the low magnetic field range
(Weiss-oscillations regime), which are absent in the one-dimensional weak
modulation case.Comment: 11 pages, 7 figures, accepted by Mod. Phys. Lett. B (March 2007
Nuclear muon-positron conversion mediated by Majorana neutrinos
We study lepton number violating (LNV) process of muon-positron conversion in
nuclei mediated by the exchange of light and heavy Majorana neutrinos. Nuclear
structure calculations have been carried out for the case of experimentally
interesting nucleus 48Ti in the framework of renormalized proton-neutron
Quasiparticle Random Phase Approximation. We demonstrate that the imaginary
part of the amplitude of light Majorana neutrino exchange mechanism gives an
appreciable contribution to the muon-positron conversion rate. This specific
feature is absent in the allied case of neutrinoless double beta decay. Using
the present neutrino oscillations, tritium beta decay, accelerator and
cosmological data we derived the limits on the effective masses of light
_{\mu e} and heavy _{\mu e} neutrinos. The expected rates of
muon-positron nuclear conversion, corresponding to these limits, were found to
be so small that even within a distant future the muon-positron conversion
experiments will hardly be able to detect the neutrino signal. Therefore,
searches for this LNV process can only rely on the presence of certain physics
beyond the trivial extension of the Standard Model by inclusion of massive
Majorana neutrinos.Comment: 28 pages, 3 figures. Added comments, references and one figure. Typos
in eqs. (18), (19) correcte
Localized Wavefunctions and Magnetic Band Structure for Lateral Semiconductor Superlattices
In this paper we present calculations on the electronic band structure of a
two-dimensional lateral superlattice subject to a perpendicular magnetic field
by employing a projection operator technique based on the ray-group of
magnetotranslation operators. We construct a new basis of appropriately
symmetrized Bloch-like wavefunctions as linear combination of well-localized
magnetic-Wannier functions. The magnetic field was consistently included in the
Wannier functions defined in terms of free-electron eigenfunctions in the
presence of external magnetic field in the symmetric gauge. Using the above
basis, we calculate the magnetic energy spectrum of electrons in a lateral
superlattice with bi-directional weak electrostatic modulation. Both a square
lattice and a triangular one are considered as special cases. Our approach
based on group theory handles the cases of integer and rational magnetic fluxes
in a uniform way and the provided basis could be convenient for further both
analytic and numerical calculations.Comment: 19 pages, 5 figures. accepted to Int. J. Mod. Phys. B (April 2006
Direct detection of supersymmetric dark matter- Theoretical rates for transitions to excited states
The recent WMAP data have confirmed that exotic dark matter together with the
vacuum energy (cosmological constant) dominate in the flat Universe.
Supersymmetry provides a natural dark matter candidate, the lightest
supersymmetric particle (LSP). Thus the direct dark matter detection is central
to particle physics and cosmology. Most of the research on this issue has
hitherto focused on the detection of the recoiling nucleus. In this paper we
study transitions to the excited states, focusing on the first excited state at
50 keV of Iodine A=127. We find that the transition rate to this excited state
is about 10 percent of the transition to the ground state. So, in principle,
the extra signature of the gammai ray following its de-excitation can be
exploited experimentally.Comment: LaTex, 13 pages, 3 postscript figures, 1 table, to appear in IJMP
Dark Matter Spin-Dependent Limits for WIMP Interactions on 19-F by PICASSO
The PICASSO experiment at SNOLAB reports new results for spin-dependent WIMP
interactions on F using the superheated droplet technique. A new
generation of detectors and new features which enable background discrimination
via the rejection of non-particle induced events are described. First results
are presented for a subset of two detectors with target masses of F of
65 g and 69 g respectively and a total exposure of 13.75 0.48 kgd. No
dark matter signal was found and for WIMP masses around 24 GeV/c new limits
have been obtained on the spin-dependent cross section on F of
= 13.9 pb (90% C.L.) which can be converted into cross section
limits on protons and neutrons of = 0.16 pb and = 2.60 pb
respectively (90% C.L). The obtained limits on protons restrict recent
interpretations of the DAMA/LIBRA annual modulations in terms of spin-dependent
interactions.Comment: Revised version, accepted for publication in Phys. Lett. B, 20 pages,
7 figure