2,177 research outputs found
Right-Handed Neutrinos as the Origin of the Electroweak Scale
The insular nature of the Standard Model may be explained if the Higgs mass
parameter is only sensitive to quantum corrections from physical states.
Starting from a scale-free electroweak sector at tree-level, we postulate that
quantum effects of heavy right-handed neutrinos induce a mass term for a scalar
weak doublet that contains the dark matter particle. In turn, below the scale
of heavy neutrinos, the dark matter sector sets the scale of the Higgs
potential. We show that this framework can lead to a Higgs mass that respects
physical naturalness, while also providing a viable scalar dark matter
candidate, realistic light neutrino masses, and the baryon asymmetry of the
Universe via leptogenesis. The proposed scenario can remain perturbative and
stable up to the Planck scale, thereby accommodating simple extensions to
include a high scale (2\times 10^{16} GeV) inflationary sector, implied by
recent measurements. In that case, our model typically predicts that the dark
matter scalar is close to 1 TeV in mass and could be accessible in near future
direct detection experiments.Comment: Revtex4, 10 pages, 6 figures. An appendix on a classically scale
invariant scenario for right-handed neutrino masses, as well as new
references added. Version accepted for publication in PR
Dark Matter from Hidden Forces
We examine the possibility that dark matter may be the manifestation of dark
forces of a hidden sector, i.e. "Dark Force = Dark Matter." As an illustrative
and minimal example we consider the hidden SU(2)_h x U(1)_h gauge group. The
hidden dynamics is indirectly coupled to the Standard Model (SM) through
kinetic mixing of U(1)_h with the U(1)_Y of hypercharge. We assume a hidden
symmetry breaking pattern analogous to that of the SM electroweak symmetry,
augmented with an extra scalar that allows both the "hidden Z boson" Z_h and
the "hidden photon" \gamma_h to be massive. The "hidden W" bosons W_h are dark
matter in this scenario. This setup can readily accommodate a potential direct
detection signal for dark matter at ~10 GeV from CDMSII-Si data. For some
choices of parameters, the model can lead to signals both in "dark matter beam"
experiments, from Z_h\to W_h W_h, as well as in experiments that look for
visible signals of dark photons, mediated by \gamma_h. Other possible
phenomenological consequences are also briefly discussed.Comment: 11 pages, 4 figures; References and additional comments added.
Results unchange
Threshold Resummed and Approximate NNLO results for W+W- Pair Production at the LHC
The next-to-leading order (NLO) QCD radiative corrections to W+W- production
at hadron colliders are well understood. We combine NLO perturbative QCD
calculations with soft-gluon resummation of threshold logarithms to find a
next-to-next-to leading logarithmic (NNLL) prediction for the total cross
section and the invariant mass distribution at the LHC. We also obtain
approximate next-to-next-to-leading order (NNLO) results for the total W+W-
cross section at the LHC which includes all contributions from the scale
dependent leading singular terms. Our result for the approximate NNLO total
cross section is the most precise theoretical prediction available.
Uncertainties due to scale variation are shown to be small when the threshold
logarithms are included. NNLL threshold resummation increases the W+W-
invariant mass distribution by ~ 3-4% in the peak region for both \sqrt{S}=8
and 14 TeV. The NNLL threshold resummed and approximate NNLO cross sections
increase the NLO cross section by 0.5-3% for \sqrt{S}=7, 8, 13, and 14 TeV.Comment: 29 pages, 7 figures, 3 tables. Discussion added to introduction,
references updated, and typos correcte
Non-resonant Collider Signatures of a Singlet-Driven Electroweak Phase Transition
We analyze the collider signatures of the real singlet extension of the
Standard Model in regions consistent with a strong first-order electroweak
phase transition and a singlet-like scalar heavier than the Standard Model-like
Higgs. A definitive correlation exists between the strength of the phase
transition and the trilinear coupling of the Higgs to two singlet-like scalars,
and hence between the phase transition and non-resonant scalar pair production
involving the singlet at colliders. We study the prospects for observing these
processes at the LHC and a future 100 TeV collider, focusing particularly
on double singlet production. We also discuss correlations between the strength
of the electroweak phase transition and other observables at hadron and future
lepton colliders. Searches for non-resonant singlet-like scalar pair production
at 100 TeV would provide a sensitive probe of the electroweak phase transition
in this model, complementing resonant di-Higgs searches and precision
measurements. Our study illustrates a strategy for systematically exploring the
phenomenologically viable parameter space of this model, which we hope will be
useful for future work.Comment: 34 pages + 4 appendices, 13 figures. Comments welcome
Shedding Light on Top Partner at the LHC
We investigate the sensitivity of the 14 TeV LHC to pair-produced top
partners () decaying into the Standard Model top quark () plus either a
gluon () or a photon (). The decays and
can be dominant when the mixing between the top partner
and top quark are negligible. In this case, the conventional decays
, , and are highly
suppressed and can be neglected. We take a model-independent approach using
effective operators for the -- and -- interactions,
considering both spin- and spin- top partners. We
perform a semi-realistic simulation with boosted top quark tagging and an
appropriate implementation of a jet-faking-photon rate. Despite a simple
dimensional analysis indicating that the branching ratios due to the
electric-magnetic coupling being much smaller than the strong force coupling,
our study shows that the LHC sensitivity to is more significant than the sensitivity to
. This is due to much smaller
backgrounds attributed to the isolated high- photon. We find that with
these decay channels and 3 ab of data, the LHC is sensitive to top
partner masses ~TeV for spin- and
spin- top partners, respectively.Comment: 33 pages, 10 figures, 7 table
NLO corrections to double Higgs boson production in the Higgs singlet model
Higgs pair production at the LHC from gluon fusion is small in the Standard Model but can be enhanced in models where a resonant enhancement is allowed. We examine the effect of a resonant contribution from a second scalar arising in a model with a gauge singlet scalar field in addition to the usual SU(2) scalar doublet, with mass up to MHβΌ600ββGeV, and discuss the interference effects in double Higgs production. The interference effects distort the double Higgs invariant mass distributions and, depending on MH, can enhance the total cross section by up to βΌ20% or decrease by βΌ30% for viable mixing parameters. We compute the next-to-leading-order QCD corrections in the large mt limit. The corrections are large and can also significantly distort kinematic distributions near the resonance peak
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