55 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
Resonance at 125 GeV: Higgs or Dilaton/Radion?
We consider the possibility that the new particle that has been observed at
125 GeV is not the Standard Model (SM) Higgs, but instead the dilaton
associated with an approximate conformal symmetry that has been spontaneously
broken. We focus on dilatons that arise from theories of technicolor, or from
theories of the Higgs as a pseudo-Nambu-Goldstone boson (pNGB), that involve
strong conformal dynamics in the ultraviolet. In the pNGB case, we are
considering a framework where the Higgs particle is significantly heavier than
the dilaton and has therefore not yet been observed. In each of the technicolor
and pNGB scenarios, we study both the case when the SM fermions and gauge
bosons are elementary, and the case when they are composites of the strongly
interacting sector. Our analysis incorporates conformal symmetry violating
effects, which are necessarily present since the dilaton is not massless, and
is directly applicable to a broad class of models that stabilize the weak scale
and involve strong conformal dynamics. Since the AdS/CFT correspondence relates
the radion in Randall-Sundrum (RS) models to the dilaton, our results also
apply to RS models with the SM fields localized on the infrared brane, or in
the bulk. We identify the parameters that can be used to distinguish the
dilatons associated with the several different classes of theories being
considered from each other, and from the SM Higgs. We perform a fit to all the
available data from several experiments and highlight the key observations to
extract these parameters. We find that at present, both the technicolor and
pNGB dilaton scenarios provide a good fit to the data, comparable to the SM
Higgs. We indicate the future observations that will help to corroborate or
falsify each scenario.Comment: 41 pages, 4 figures. Analysis updated using current theoretical
limits on dimensions of CFT operators. References added. Version to appear on
JHE
Cosmological Signatures of a Mirror Twin Higgs
We explore the cosmological signatures associated with the twin baryons,
electrons, photons and neutrinos in the Mirror Twin Higgs framework. We
consider a scenario in which the twin baryons constitute a subcomponent of dark
matter, and the contribution of the twin photon and neutrinos to dark radiation
is suppressed due to late asymmetric reheating, but remains large enough to be
detected in future cosmic microwave background (CMB) experiments. We show that
this framework can lead to distinctive signals in large scale structure and in
the cosmic microwave background. Baryon acoustic oscillations in the mirror
sector prior to recombination lead to a suppression of structure on large
scales, and leave a residual oscillatory pattern in the matter power spectrum.
This pattern depends sensitively on the relative abundances and ionization
energies of both twin hydrogen and helium, and is therefore characteristic of
this class of models. Although both mirror photons and neutrinos constitute
dark radiation in the early universe, their effects on the CMB are distinct.
This is because prior to recombination the twin neutrinos free stream, while
the twin photons are prevented from free streaming by scattering off twin
electrons. In the Mirror Twin Higgs framework the relative contributions of
these two species to the energy density in dark radiation is predicted, leading
to testable effects in the CMB. These highly distinctive cosmological
signatures may allow this class of models to be discovered, and distinguished
from more general dark sectors.Comment: 30 pages, 6 figures; added new discussions and figures; references
added; matches published versio
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