1,566 research outputs found
Nucleon strange quark content from two-flavor lattice QCD with exact chiral symmetry
Strange quark content of the nucleon is calculated in dynamical lattice QCD
employing the overlap fermion formulation. For this quantity, exact chiral
symmetry guaranteed by the Ginsparg-Wilson relation is crucial to avoid large
contamination due to a possible operator mixing with . Gauge
configurations are generated with two dynamical flavors on a 16^3 x 32 lattice
at a lattice spacing a \simeq 0.12fm. We directly calculate the relevant
three-point function on the lattice including a disconnected strange quark loop
utilizing the techniques of all-to-all quark propagator and low-mode averaging.
Our result f_{T_s} = 0.032(8)(22), is in good agreement with our previous
indirect estimate using the Feynman-Hellmann theorem.Comment: 31 pages, 22 figures; version published in PR
Search for Higgs Bosons in SUSY Cascade Decays and Neutralino Dark Matter
The Minimal Supersymmetric Extension of the Standard Model (MSSM) is a well
motivated theoretical framework, which contains an extended Higgs sector,
including a light Higgs with Standard Model-like properties in most of the
parameter space. Due to the large QCD background, searches for such a Higgs,
decaying into a pair of bottom quarks, is very challenging at the LHC. It has
been long realized that the situation may be ameliorated by searching for Higgs
bosons in supersymmetric decay chains. Moreover, it has been recently suggested
that the bobber decay channel may be observed in standard production channels
by selecting boosted Higgs bosons, which may be easily identified from the QCD
background. Such boosted Higgs bosons are frequent in the MSSM, since they are
produced from decays of heavy colored supersymmetric particles. Previous works
have emphasized the possibility of observing boosted Higgs bosons in the light
higgsino region. In this work, we study the same question in the regions of
parameter space consistent with a neutralino dark matter relic density,
analyzing its dependence on the non-standard Higgs boson, slepton and squark
masses, as well as on the condition of gaugino mass unification. In general, we
conclude that, provided sleptons are heavier than the second lightest
neutralinos, the presence of boosted Higgs is a common MSSM feature, implying
excellent prospects for observation of the light MSSM Higgs boson in the near
future.Comment: 30 pages, 9 figures. v2: New Xenon 100 results implemented, version
to appear in PR
Discrete R-symmetry anomalies in heterotic orbifold models
Anomalies of discrete R-symmetries appearing in heterotic orbifold models are
studied. We find that the mixed anomalies for different gauge groups satisfy
the universal Green-Schwarz (GS) condition, indicating that these anomalies are
canceled by the GS mechanism. An exact relation between the anomaly
coefficients of the discrete R-symmetries and one-loop beta-function
coefficients is obtained. We also find that the discrete R-symmetries have a
good chance to be unbroken down to the supersymmetry breaking scale. Even below
this scale a subgroup is unbroken, which may be an origin of the R-parity
of the minimal supersymmetric standard model. Relations between the R-symmetry
anomalies and T-duality anomalies are also investigated.Comment: 19 pages, no figur
Dark matter in the classically conformal B-L model
When the classically conformal invariance is imposed on the minimal gauged
B-L extended Standard Model (SM), the B-L gauge symmetry is broken by the
Coleman-Weinberg mechanism naturally at the TeV scale. Introducing a new Z_2
parity in the model, we investigate phenomenology of a right-handed neutrino
dark matter whose stability is ensured by the parity. We find that the relic
abundance of the dark matter particle can be consistent with the observations
through annihilation processes enhanced by resonances of either the SM Higgs
boson, the B-L Higgs boson or the B-L gauge boson (Z' boson). Therefore, the
dark matter mass is close to half of one of these boson masses. Due to the
classically conformal invariance and the B-L gauge symmetry breaking via the
Coleman-Weinberg mechanism, Higgs boson masses, Z' boson mass and the dark
matter mass are all related, and we identify the mass region to be consistent
with experimental results. We also calculate the spin-independent cross section
of the dark matter particle off with nucleon and discuss implications for
future direct dark matter search experiments.Comment: 13 pages, 4 figure
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