1,235 research outputs found
Interplay of Scalar and Fermionic Components in a Multi-component Dark Matter Scenario
We explore the multi-component dark matter (DM) scenario considered in a
simple extension of the standard model with an inert scalar doublet and a
singlet fermionic field providing the two DM candidates. The DM states are made
stable under the unbroken discrete symmetry. An additional
gauge singlet scalar field is introduced to facilitate the interaction of the
dark fermion with the visible sector. Presence of a charged fermionic field
having the same charge as that of the inert scalar field allows exploring
the dark matter mass regions otherwise disallowed, like in the standard Inert
Doublet Model (IDM) scenarios. With these arrangements, it is shown that the
light DM scenario and the desert region in the intermediate mass range of DM in
the standard IDM case can be made compatible with the relic density bounds and
direct detection limits. Further, detailed parameter space study is carried out
keeping the coexistence of both the scalar and fermionic components in focus,
showing that sizable parameter space regions are available for the entire mass
range of GeV.Comment: 19 pages, 19 figures, appendix added, some minor corrections to main
tex
Two Higgs bosons near 125 GeV in the NMSSM: beyond the narrow width approximation
In the next-to-minimal supersymmetric (NMS) Standard Model (SM), it is
possible for either one of the additional singlet-like scalar and pseudoscalar
Higgs bosons to be almost degenerate in mass with the ~125 GeV SM-like Higgs
state. In the real NMSSM (rNMSSM), when the mass difference between two scalar
states is comparable to their individual total decay widths, the quantum
mechanical interference, due to the relevant diagonal as well as off-diagonal
terms in the propagator matrix, between them can become sizable. This
possibility invalidates usage of the narrow width approximation (NWA) to
compute the cross section for the production of a di-photon pair with a given
invariant mass via resonant Higgs boson(s) in the gluon fusion process at the
Large Hadron Collider (LHC). When, motivated by the baryon asymmetry of the
universe, CP-violating (CPV) phases are explicitly invoked in the Higgs sector
of the NMSSM, all the interaction eigenstates mix to give five CP-indefinite
physical Higgs bosons. In this scenario, the interference effects due the
off-diagonal terms in the Higgs mass matrix that mix the pseudoscalar-like
state with the SM-like one can also become significant, when these two are
sufficiently mass-degenerate. We perform a detailed analysis, in both the real
and complex NMSSM, of these interference effects, when the full propagator
matrix is taken into account, in the production of a photon pair with an
invariant mass near 125 GeV through gluon fusion. We find that these effects
can account for up to ~40% of the total cross section for certain model
parameter configurations. We also investigate how such mutually interfering
states contributing to the ~125 GeV signal observed at the LHC can be
distinguished from a single resonance.Comment: 26 pages, 9 figures. Typos corrected, some figures and text improved.
Version published in EPJ
Quantum interference among heavy NMSSM Higgs bosons
In the Next-to-Minimal Supersymmetric Standard Model (NMSSM), it is possible
to have strong mass degeneracies between the new singlet-like scalar and the
heavy doublet-like scalar, as well as between the singlet-like and doublet-like
pseudoscalar Higgs states. When the difference in the masses of such states is
comparable with the sum of their widths, the quantum mechanical interference
between their propagators can become significant. We study these effects by
taking into account the full Higgs boson propagator matrix in the calculation
of the production process of pairs in gluon fusion at the Large
Hadron Collider (LHC). We find that, while these interference effects are
sizeable, they are not resolvable in terms of the distributions of differential
cross sections, owing to the poor detector resolution of the
invariant mass. They are, however, identifiable via the inclusive cross
sections, which are subject to significant variations with respect to the
standard approaches, wherein the propagating Higgs bosons are treated
independently from one another. We quantify these effects for several
representative benchmark points, extracted from a large set of points, obtained
by numerical scanning of the NMSSM parameter space, that satisfy the most
important experimental constraints currently available.Comment: 18 pages, 5 figures, 2 tables. Revised benchmark points and figures,
overall results and conclusions unchanged. Version to appear in PR
Direct searches of Type III seesaw triplet fermions at high energy collider
The signatures of heavy fermionic triplets () arising in scenarios
like Type III seesaw model are probed through their direct production and
subsequent decay at high energy electron-positron collider. Unlike the case of
LHC, the production process has strong dependence on the mixing parameter
(), making the leptonic collider unique to probe such mixing. We
have established that with suitably chosen kinematic cuts, a 1 TeV
collider could probe the presence of of mass in the range of 500 GeV
having with a few inverse femto barn luminosity through single
production. The cross section is found to be not sufficient to probe the case
of triplet-muon mixing through single triplet production. On the other hand,
the pair production considered at 2 TeV centre of mass energy is capable of
probing both the mixing scenarios efficiently. Studying the mass reach,
presence of charged fermionic triplets upto a mass of about 980 GeV could be
established at level through single production at a 1 TeV
collider with moderate luminosity of 100 fb, assuming . The
pair production case requires larger luminosity, as the cross section is
smaller in this case. With an integrated luminosity of 300 fb, the mass
reach in this case is close to 1 TeV with triplet-muon mixing, while it is
slightly lower at about 950 GeV in the case of .Comment: 26 pages, 5 Figure
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