1,451 research outputs found
Supernova matter at subnuclear densities as a resonant Fermi gas: Enhancement of neutrino rates
At low energies nucleon-nucleon interactions are resonant and therefore
supernova matter at subnuclear densities has many similarities to atomic gases
with interactions dominated by a Feshbach resonance. We calculate the rates of
neutrino processes involving nucleon-nucleon collisions and show that these are
enhanced in mixtures of neutrons and protons at subnuclear densities due to the
large scattering lengths. As a result, the rate for neutrino pair
bremsstrahlung and absorption is significantly larger below 10^{13} g cm^{-3}
compared to rates used in supernova simulations.Comment: 5 pages, 4 figures, published version, NORDITA-2014-2
Triple product correlations in top squark decays
We propose several T-odd asymmetries in the decay chains of the top squarks
and and , for . We
calculate the asymmetries within the Minimal Supersymmetric Standard Model with
complex parameters , and . We give the analytic formulae for
the decay distributions. We present numerical results for the asymmetries and
estimate the event rates necessary to observe them. The largest T-odd asymmetry
can be as large as 40%.Comment: 26 pages, 5 figures; misprints corrected; reference adde
Interference of Higgs boson resonances in mu^+ mu^- -> neutralino_i neutralino_j with longitudinal beam polarization
We study the interference of resonant Higgs boson exchange in neutralino
production in \mu^+ \mu^- annihilation with longitudinally polarized beams. We
use the energy distribution of the decay lepton in the process \neutralino_j
\to \ell^\pm \slepton^\mp to determine the polarization of the neutralinos. In
the CP conserving Minimal Supersymmetric Standard Model a non-vanishing
asymmetry in the lepton energy spectrum is caused by the interference of Higgs
boson exchange channels with different CP eigenvalues. The contribution of this
interference is large if the heavy neutral bosons H and A are nearly
degenerate. We show that the asymmetry can be used to determine the couplings
of the neutral Higgs bosons to the neutralinos. In particular, the asymmetry
allows to determine the relative phase of the couplings. We find large
asymmetries and cross sections for a set of reference scenarios with nearly
degenerate neutral Higgs bosons.Comment: 20 pages, 6 figures, minor typos corrected, to appear in Eur. Phys.
J.
CP asymmetries in the supersymmetric trilepton signal at the LHC
In the CP-violating Minimal Supersymmetric Standard Model, we study the
production of a neutralino-chargino pair at the LHC. For their decays into
three leptons, we analyze CP asymmetries which are sensitive to the CP phases
of the neutralino and chargino sector. We present analytical formulas for the
entire production and decay process, and identify the CP-violating
contributions in the spin correlation terms. This allows us to define the
optimal CP asymmetries. We present a detailed numerical analysis of the cross
sections, branching ratios, and the CP observables. For light neutralinos,
charginos, and squarks, the asymmetries can reach several 10%. We estimate the
discovery potential for the LHC to observe CP violation in the trilepton
channel.Comment: 39 pages, 8 figures, version to appear in EPJC, discussion(s) added,
typo in (D.79), (D.118) corrected, new Fig. 7; The European Physical Journal
C, Volume 72, Issue 3, 201
A description of the neutralino observables in terms of projectors
Applying Jarlskog's treatment of the CKM matrix, to the neutralino mass
matrix in MSSM for real soft gaugino SUSY breaking and -parameters, we
construct explicit analytical expressions for the four projectors which acting
on any neutralino state project out the mass eigenstates. Analytical
expressions for the neutralino mass eigenvalues in terms of the various SUSY
parameters, are also given. It is shown that these projectors and mass
eigenvalues are sufficient to describe any physical observable involving
neutralinos, to any order of perturbation theory. As an example, the cross section at tree level is given in
terms of these projectors. The expected magnitude of their various matrix
elements in plausible SUSY scenarios is also discussed.Comment: 14 pages, no figures. Version to appear in Phys. Rev. D. e-mail:
[email protected]
Top Squarks and Bottom Squarks in the MSSM with Complex Parameters
We present a phenomenological study of top squarks (~t_1,2) and bottom
squarks (~b_1,2) in the Minimal Supersymmetric Standard Model (MSSM) with
complex parameters A_t, A_b, \mu and M_1. In particular we focus on the CP
phase dependence of the branching ratios of (~t_1,2) and (~b_1,2) decays. We
give the formulae of the two-body decay widths and present numerical results.
We find that the effect of the phases on the (~t_1,2) and (~b_1,2) decays can
be quite significant in a large region of the MSSM parameter space. This could
have important implications for (~t_1,2) and (~b_1,2) searches and the MSSM
parameter determination in future collider experiments. We have also estimated
the accuracy expected in the determination of the parameters of ~t_i and ~b_i
by a global fit of the measured masses, decay branching ratios and production
cross sections at e^+ e^- linear colliders with polarized beams. Analysing two
scenarios, we find that the fundamental parameters apart from A_t and A_b can
be determined with errors of 1% to 2%, assuming an integrated luminosity of 1
ab^-1 and a sufficiently large c.m.s. energy to produce also the heavier ~t_2
and ~b_2 states. The parameter A_t can be determined with an error of 2 - 3%,
whereas the error on A_b is likely to be of the order of 50%.Comment: 31 pages, 8 figures, comments and references added, conclusions
unchanged; version to appear in Phys. Rev.
Improved full one--loop corrections to A^0 -> \sq_1 \sq_2 and \sq_2 -> \sq_1 A^0
We calculate the full electroweak one-loop corrections to the decay of the
CP-odd Higgs boson A^0 into scalar quarks in the minimal supersymmetric
extension of the Standard Model (MSSM). Due to the complex structure of the
electroweak sector a proper renormalization of many parameters in the on-shell
renormalization scheme is necessary. For the decay into sbottom quarks,
especially for large tanb, the corrections can be very large in the on-shell
renormalization scheme, which makes the perturbation series unreliable. We
solve this problem by an appropriate definition of the tree-level coupling in
terms of running quark masses and running trilinear couplings A_q. We also
discuss the decay of heavy scalar quarks into light scalar quarks and A^0. We
find that the corrections are significant and therefore cannot be neglected.Comment: 15 pages, 9 figures, Fig. 8 correcte
CP-odd observables in neutralino production with transverse e+ and e- beam polarization
We consider neutralino production and decay e^+e^ --> chi^0_i chi^0_j,
chi^0_j --> chi^0_1 f \bar{f} at a linear collider with transverse e^+ and e^-
beam polarization. We propose CP asymmetries by means of the azimuthal
distribution of the produced neutralinos and of that of the final leptons,
while taking also into account the subsequent decays of the neutralinos. We
include the complete spin correlations between production and decay. Our
framework is the Minimal Supersymmetric Standard Model with complex parameters.
In a numerical study we show that there are good prospects to observe these CP
asymmetries at the International Linear Collider and estimate the accuracy
expected for the determination of the phases in the neutralino sector.Comment: 30 pages, minor changes in the introduction, references adde
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