1,200 research outputs found
Gravitino Dark Matter with Weak-Scale Right-Handed Sneutrino
We consider cosmological implications of supersymmetric models with
right-handed (s)neutrinos where the neutrino masses are purely Dirac-type. We
pay particular attention to the case where gravitino is the lightest
superparticle while one of the right-handed sneutrinos is next-to-the-lightest
superparticle. We study constraints from big-bang nuleosynthesis and show that
the constraints could be relaxed compared to the case without right-handed
sneutrinos. As a result, the gravitino-dark-matter scenario becomes viable with
relatively large value of the gravitino mass. We also discuss constraints from
the structure formation; in our model, the free-streaming length of the
gravitino dark matter may be as long as O(1 Mpc), which is comparable to the
present observational upper bound on the scale of free-streaming.Comment: 18 pages, 6 figure
Search for the Top Partner at the LHC using Multi-b-Jet Channels
Vector-like quarks are introduced in various new physics models beyond the
standard model (SM) at the TeV scale. We especially consider the case that the
quark is singlet (triplet) under the SU(2) (SU(3)) gauge group and
couples only to the third generation quarks of the SM. The vector-like quark of
this kind is often called a top partner. The top partoner decays into
and . In the ATLAS and CMS collaborations, the top partner has
been searched in the final states of and , while the search based on
the decay mode has not been started yet. However, the decay into
is important since it is significantly enhanced if some strong dynamics
exists in the TeV scale. In the presence of a light higgs boson, the decay mode
followed by produces three bottom quarks. We study
the sensitivity for the top partner using multi-b-jet events at the 8 TeV run
of the LHC experiment. The multi-b-jet eventss turn out to play a complementary
role to the existing and searches by the ATLAS and CMS
collaborations.Comment: 26 pages, 9 figures, 10 Table
Explosive Dark Matter Annihilation
If the Dark Matter (DM) in the Universe has interactions with the
standard-model particle, the pair annihilation may give the imprints in the
cosmic ray. In this paper we study the pair annihilation processes of the DM,
which is neutral, however has the electroweak (EW) gauge non-singlet. In this
estimation the non-relativistic (NR) effective theory in the EW sector is a
suitable technique. We find that if the DM mass is larger than about 1 TeV, the
attractive Yukawa potentials induced by the EW gauge bosons have significant
effects on the DM annihilation processes, and the cross sections may be
enhanced by several orders of magnitude, due to the zero energy resonance under
the potentials. Especially, the annihilation to two 's might have a
comparable cross section to other tree-level processes, while the cross section
under the conventional calculation is suppressed by a loop factor. We also
discuss future sensitivities to the ray from the galactic center by
the GLAST satellite detector and the Air Cerenkov Telescope (ACT) arrays.Comment: 5 pages, 6 Postscript figures, revte
Holographic Chern-Simons Defects
We study SU(N) Yang-Mills-Chern-Simons theory in the presence of defects that
shift the Chern-Simons level from a holographic point of view by embedding the
system in string theory. The model is a D3-D7 system in Type IIB string theory,
whose gravity dual is given by the AdS soliton background with probe D7-branes
attaching to the AdS boundary along the defects. We holographically renormalize
the free energy of the defect system with sources, from which we obtain the
correlation functions for certain operators naturally associated to these
defects. We find interesting phase transitions when the separation of the
defects as well as the temperature are varied. We also discuss some
implications for the Fractional Quantum Hall Effect and for two-dimensional
QCD.Comment: 56 pages, 19 figures, v2: sign convention for CS level in terms of
number of D7 branes switched, UV behavior of one and two point functions
added in sec. 5.4.1 and 5.4.3, references added, typos correcte
Heavy Fermion Bound States for Diphoton Excess at 750GeV Collider and Cosmological Constraints
A colored heavy particle with sufficiently small width may form
non-relativistic bound states when they are produced at the large hadron
collider\,(LHC), and they can annihilate into a diphoton final state. The
invariant mass of the diphoton would be around twice of the colored particle
mass. In this paper, we study if such bound state can be responsible for the
750 GeV diphoton excess reported by ATLAS and CMS. We found that the best-fit
signal cross section is obtained for the SU(2) singlet colored fermion
with . Having such an exotic hypercharge, the particle is expected to
decay through some higher dimensional operators, consistent with the small
width assumption. The decay of may involve a stable particle , if
both and are odd under some conserved symmetry. In that case,
the particle suffers from the constraints of jets + missing searches
by ATLAS and CMS at 8 TeV and 13 TeV. We found that such a scenario still
survives if the mass difference between and is above 30 GeV
for GeV. Even assuming pair annihilation of is small, the
relic density of is small enough if the mass difference between and
is smaller than 40 GeV
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