100 research outputs found
Identifying Sneutrino Dark Matter: Interplay between the LHC and Direct Search
Under R-parity, the lightest supersymmetric particle (LSP) is stable and may
serve as a good dark matter candidate. The R-parity can be naturally introduced
with a gauge origin at TeV scale. We go over why a TeV scale B-L gauge
extension of the minimal supersymmetric standard model (MSSM) is one of the
most natural, if not demanded, low energy supersymmetric models. In the
presence of a TeV scale Abelian gauge symmetry, the (predominantly)
right-handed sneutrino LSP can be a good dark matter candidate. Its
identification at the LHC is challenging because it does not carry any standard
model charge. We show how we can use the correlation between the LHC
experiments (dilepton resonance signals) and the direct dark matter search
experiments (such as CDMS and XENON) to identify the right-handed sneutrino LSP
dark matter in the B-L extended MSSM.Comment: 5 pages, 3 figure
Higgs-Higgsino-gaugino induced two loop electric dipole moments
We compute the complete set of Higgs-mediated chargino-neutralino two-loop contributions to the electric dipole moments of the electron and neutron in the minimal supersymmetric standard model (MSSM). We study the dependence of these contributions on the parameters that govern CP-violation in the MSSM gauge-gaugino-Higgs-Higgsino sector. We find that contributions mediated by the exchange of WH± and ZA0 pairs, where H± and A0 are the charged and CP-odd Higgs scalars, respectively, are comparable to or dominate over those mediated by the exchange of neutral gauge bosons and CP-even Higgs scalars. We also emphasize that the result of this complete set of diagrams is essential for the full quantitative study of a number of phenomenological issues, such as electric dipole moment searches and their implications for electroweak baryogenesis
Fixing Two-Nucleon Weak-Axial Coupling L_{1,A} From mu-d Capture
We calculate the muon capture rate on the deuteron to next-to-next-to-leading
order in the pionless effective field theory. The result can be used to
constrain the two-nucleon isovector axial coupling L_{1,A} to +/- 2 fm^3 if the
muon capture rate is measured to 2% level. From this, one can determine the
neutrino-deuteron break up reactions and the pp-fusion cross section in the sun
to a same level of accuracy.Comment: replaced by the version appearing in the PR
A SUSY SO(10) GUT Model with Lopsided Structure
The standard model (SM) of elementary particles
has been established for more than 30 years and tested by a large
number of experiments. However, because of the naturalness problem
of the electroweak symmetry breaking scale and a large number of
unexplained parameters in SM, physicists have been looking for a
more fundamental theory. Supersymmetry (SUSY) and grand
unification are two appealing concepts that have been mostly
implemented to build candidates for beyond SM theories. SUSY helps
to stabilize the scale of electroweak symmetry breaking, and grand
unification embeds the SM gauge groups into larger and more
fundamental gauge groups.
Neutrino oscillations, signaling massive neutrinos, are the first
direct evidence of beyond SM physics. A tiny neutrino mass can be
elegantly explained by the seesaw mechanism. The neutrino masses
from this mechanism are of Majorana type and therefore break the
B-L (baryon number minus lepton number) symmetry. A favorable
framework of studying neutrino masses and oscillations is the
SO(10) grand unification theory (GUT) which naturally accommodates
a B-L breaking. The same B-L breaking can also facilitate
baryogenesis via a leptogenesis scenario. This provides an
interesting correlation between these two pieces of phenomenology.
This thesis presents a realistic SUSY SO(10) GUT model with
lopsided structure, which generates the correct masses and mixing
of neutrinos and produces the right amount of baryon asymmetry.
One of the most characteristic features of this model is the
lopsided mass matrices structure. We examine observables in B
decays that are sensitive to this structure, and find a specific
pattern of predictions that can be used to test this type of
models
Bino-driven electroweak baryogenesis with highly suppressed electric dipole moments
It is conventional wisdom that successful electroweak baryogenesis in the Minimal Supersymmetric extension of the Standard Model (MSSM) is in tension with the non-observation of electric dipole moments (EDMs), since the level of CP-violation responsible for electroweak baryogenesis is believed to generate unavoidably large EDMs. We show that CP-violation in the bino–Higgsino sector of the MSSM can account for successful electroweak baryogenesis without inducing large EDMs. This observation weakens the correlation between electroweak baryogenesis and EDMs, and makes the bino-driven electroweak baryogenesis scenario the least constrained by EDM limits. Taking this observation together with the requirement of a strongly first-order electroweak phase transition, we argue that a bino-driven scenario with a light stop is the most phenomenologically viable MSSM electroweak baryogenesis scenario
Deuteron Compton Scattering in Effective Field Theory: Spin-Dependent Cross Sections and Asymmetries
Polarized Compton scattering on the deuteron is studied in nuclear effective
field theory. A set of tensor structures is introduced to define 12 independent
Compton amplitudes. The scalar and vector amplitudes are calculated up to
in low-energy power counting. Significant
contribution to the vector amplitudes is found to come from the spin-orbit type
of relativistic corrections. A double-helicity dependent cross section
is calculated to the same
order, and the effect of the nucleon isoscalar spin-dependent polarizabilities
is found to be smaller than the effect of isoscalar spin-independent ones.
Contributions of spin-independent polarizabilities are investigated in various
asymmetries, one of which has as large as 12 (26) percent effect at the
center-of-mass photon energy 30 (50) MeV.Comment: 22 pages, 8 figures included, replaced with the version submitted to
PR
Sum Rules and Spin-Dependent Polarizabilities of the Deuteron in Effective Field Theory
We construct sum rules for the forward vector and tensor polarizabilities for
any spin- target and apply them to the spin-1 deuteron. We calculate these
polarizabilities of the deuteron to the next-to-leading order in the pionless
effective field theory.Comment: 10 pages, figures include
Drell-Hearn-Gerasimov Sum-Rule for the Deuteron in Nuclear Effective Field Theory
The Drell-Hearn-Gerasimov sum rule for the deuteron is studied in nuclear
effective field theory. The low-energy theorem for the spin-dependent Compton
amplitude is derived to the next-to-leading order in low-energy
expansion. The spin-dependent photodisintegration cross section
is calculated to the same order, and its contribution to
the dispersive integral is evaluated.Comment: 8 pages, 2 figure
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