6,374 research outputs found
Decoding the Mechanism for the Origin of Dark Matter in the Early Universe Using LHC Data
It is shown that LHC data can allow one to decode the mechanism by which dark
matter is generated in the early universe in supersymmetric theories. We focus
on two of the major mechanisms for such generation of dark matter which are
known to be the Stau Coannihilation (Stau-Co) where the neutralino is typically
Bino like and annihilation on the Hyperbolic Branch (HB) where the neutralino
has a significant Higgsino component. An investigation of how one may
discriminate between the Stau-Co region and the HB region using LHC data is
given for the mSUGRA model. The analysis utilizes several signatures including
multi leptons, hadronic jets, b-tagging, and missing transverse momentum. A
study of the SUSY signatures reveals several correlated smoking gun signals
allowing a clear discrimination between the Stau-Co and the HB regions where
dark matter in the early universe can originate.Comment: 7 pages, 5 figs, 2 columns, Accepted for publication in Physical
Review
CP Violation and Dark Matter
A brief review is given of the effects of CP violation on the direct
detection of neutralinos in dark matter detectors. We first summarize the
current developments using the cancellation mechanism which allows for the
existence of large CP violating phases consistent with experimental limits on
the electron and on the neutron electric dipole moments in a broad class of
SUSY, string and D brane models. We then discuss their effects on the
scattering of neutralinos from quarks and on the event rates. It is found that
while CP effects on the event rates can be enormous such effects are reduced
significantly with the imposition of the EDM constraints. However, even with
the inclusion of the EDM constraints the effects are still very significant and
should be included in a precision prediction of event rates in any SUSY, string
or D brane model.Comment: Based on an invited talk at the conference "Sources and Detection of
Dark Matter in the Universe", at Marina del Rey, CA, Feb. 23-25, 2000; 12
pages, Latex including 2 figure
The Role of in Two-pion Exchange Three-nucleon Potential
In this paper we have studied the two-pion exchange three-nucleon potential
using an approximate chiral symmetry of the
strong interaction. The off-shell pion-nucleon scattering amplitudes obtained
from the Weinberg Lagangian are supplemented with contributions from the
well-known -term and the exchange. It is the role of the
-resonance in , which we have investigated in detail in the
framework of the Lagrangian field theory. The -contribution is quite
appreciable and, more significantly, it is dependent on a parameter Z which is
arbitrary but has the empirical bounds . We find that the
-contribution to the important parameters of the depends
on the choice of a value for Z, although the correction to the binding energy
of triton is not expected to be very sensitive to the variation of Z within its
bounds.Comment: 14 pages, LaTe
A phenomenological model for magnetoresistance in granular polycrystalline colossal magnetoresistive materials: the role of spin polarised tunnelling at the grain boundaries
It has been observed that in bulk and polycrystalline thin films of collossal
magnetoresistive (CMR) materials the magnetoresistance follows a different
behaviour compared to single crystals or single crystalline films below the
ferromagnetic transition temperature Tc. In this paper we develop a
phenomenological model to explain the magnetic field dependence of resistance
in granular CMR materials taking into account the spin polarised tunnelling at
the grain boundaries. The model has been fitted to two systems, namely,
La0.55Ho0.15Sr0.3MnO3 and La1.8Y0.5Ca0.7Mn2O7. From the fitted result we have
separated out, in La0.55Ho0.15Sr0.3MnO3, the intrinsic contribution from the
intergranular contribution to the magnetoresistance coming from spin polarised
tunnelling at the grain boundaries. It is observed that the temperature
dependence of the intrinsic contribution to the magnetoresistance in
La0.55Ho0.15Sr0.3MnO3 follows the prediction of double exchange model for all
values of field.Comment: 14 pages + 5 figures, postscript (to appear in Journal of Applied
Physics
Regularization Dependence of Running Couplings in Softly Broken Supersymmetry
We discuss the dependence of running couplings on the choice of
regularization method in a general softly-broken N=1 supersymmetric theory.
Regularization by dimensional reduction respects supersymmetry, but standard
dimensional regularization does not. We find expressions for the differences
between running couplings in the modified minimal subtraction schemes of these
two regularization methods, to one loop order. We also find the two-loop
renormalization group equations for gaugino masses in both schemes, and discuss
the application of these results to the Minimal Supersymmetric Standard Model.Comment: 11 pages. v2: Signs of equations (1.2) and (4.2) are fixe
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