15,027 research outputs found
Exploring a Dark Sector Through the Higgs Portal at a Lepton Collider
We investigate the prospects for detecting a hidden sector at an
collider. The hidden sector is assumed to be composed of invisible particles
that carry no charges under the Standard Model gauge interactions, and whose
primary interactions with ordinary matter are through the Higgs portal. We
consider both the cases when the decays of an on-shell Higgs into a pair of
hidden sector particles are kinematically allowed, and the case when such
decays are kinematically forbidden. We find that at collider energies below a
TeV, the most sensitive channel involves production of an on-shell or off-shell
Higgs in association with a Z boson, and the subsequent decay of the Higgs into
invisible hidden sector states. Focusing on this channel, we find that with
order a thousand inverse fb of data at 250 GeV, the decay branching fraction of
an on-shell Higgs to invisible hidden sector states can be constrained to lie
below half a percent. The corresponding limits on Higgs portal dark matter will
be stronger than the bounds from current and upcoming direct detection
experiments in much of parameter space. With the same amount of data at 500
GeV, assuming order one couplings, decays of an off-shell Higgs to hidden
sector states with a total mass up to about 200 GeV can also be probed. Both
the on-shell and off-shell cases represent a significant improvement in
sensitivity when compared to the Large Hadron Collider (LHC).Comment: 7 pages, 6 figures, minor revisions, with added references, new
version to appear in Physics Letters
Delayed Onset and Fast Rise of Prompt Optical-UV Emission from Gamma-Ray Bursts in Molecular Clouds
Observations imply that long \gamma-ray bursts (GRBs) are originated from
explosions of massive stars, therefore they may occur in the molecular clouds
where their progenitors were born. We show here that the prompt optical-UV
emission from GRBs may be delayed due to the dust extinction, which can well
explain the observed optical delayed onset and fast rise in GRB 080319B. The
density and the size of the molecular cloud around GRB 080319B are roughly
constrained to be \sim10^3cm^{-3} and \sim 8pc, respectively. We also
investigate the other GRBs with prompt optical-UV data, and find similar values
of the densities and sizes of the local molecular clouds. The future
observations of prompt optical-UV emission from GRBs in subsecond timescale,
e.g., by UFFO-Pathfinder and SVOM-GWAC, will provide more evidence and probes
of the local GRB environments.Comment: 15 pages, 5 figures, RAA 13 (2013) 57-70, typo correctio
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