639 research outputs found
Inflation and dark matter in two Higgs doublet models
We consider the Higgs inflation in the extension of the Standard Model with
two Higgs doublets coupled to gravity non-minimally. In the presence of an
approximate global U(1) symmetry in the Higgs sector, both radial and angular
modes of neutral Higgs bosons drive inflation where large non-Gaussianity is
possible from appropriate initial conditions on the angular mode. We also
discuss the case with single-field inflation for which the U(1) symmetry is
broken to a Z_2 subgroup. We show that inflationary constraints, perturbativity
and stability conditions restrict the parameter space of the Higgs quartic
couplings at low energy in both multi- and single-field cases. Focusing on the
inert doublet models where Z_2 symmetry remains unbroken at low energy, we show
that the extra neutral Higgs boson can be a dark matter candidate consistent
with the inflationary constraints. The doublet dark matter is always heavy in
multi-field inflation while it can be light due to the suppression of the
co-annihilation in single-field inflation. The implication of the extra quartic
couplings on the vacuum stability bound is also discussed in the light of the
recent LHC limits on the Higgs mass.Comment: (v1) 28 pages, 8 figures; (v2) 29 pages, a new subsection 3.3 added,
references added and typos corrected, to appear in Journal of High Energy
Physic
A SM-like Higgs near 125 GeV in low energy SUSY: a comparative study for MSSM and NMSSM
Motivated by the recent LHC hints of a Higgs boson around 125 GeV, we assume
a SM-like Higgs with the mass 123-127 GeV and study its implication in low
energy SUSY by comparing the MSSM and NMSSM. We consider various experimental
constraints at 2-sigma level (including the muon g-2 and the dark matter relic
density) and perform a comprehensive scan over the parameter space of each
model. Then in the parameter space which is allowed by current experimental
constraints and also predicts a SM-like Higgs in 123-127 GeV, we examine the
properties of the sensitive parameters (like the top squark mass and the
trilinear coupling A_t) and calculate the rates of the di-photon signal and the
VV^* (V=W,Z) signals at the LHC. Our typical findings are: (i) In the MSSM the
top squark and A_t must be large and thus incur some fine-tuning, which can be
much ameliorated in the NMSSM; (ii) In the MSSM a light stau is needed to
enhance the di-photon rate of the SM-like Higgs to exceed its SM prediction,
while in the NMSSM the di-photon rate can be readily enhanced in several ways;
(iii) In the MSSM the signal rates of pp -> h -> VV^* at the LHC are never
enhanced compared with their SM predictions, while in the NMSSM they may get
enhanced significantly; (iv) A large part of the parameter space so far
survived will be soon covered by the expected XENON100(2012) sensitivity
(especially for the NMSSM).Comment: Version in JHEP (refs added
Decoupling property of the supersymmetric Higgs sector with four doublets
In supersymmetric standard models with multi Higgs doublet fields,
selfcoupling constants in the Higgs potential come only from the D-terms at the
tree level. We investigate the decoupling property of additional two heavier
Higgs doublet fields in the supersymmetric standard model with four Higgs
doublets. In particular, we study how they can modify the predictions on the
quantities well predicted in the minimal supersymmetric standard model (MSSM),
when the extra doublet fields are rather heavy to be measured at collider
experiments. The B-term mixing between these extra heavy Higgs bosons and the
relatively light MSSM-like Higgs bosons can significantly change the
predictions in the MSSM such as on the masses of MSSM-like Higgs bosons as well
as the mixing angle for the two light CP-even scalar states. We first give
formulae for deviations in the observables of the MSSM in the decoupling region
for the extra two doublet fields. We then examine possible deviations in the
Higgs sector numerically, and discuss their phenomenological implications.Comment: 26 pages, 24 figures, text sligtly modified,version to appear in
Journal of High Energy Physic
Higgs decay to dark matter in low energy SUSY: is it detectable at the LHC ?
Due to the limited statistics so far accumulated in the Higgs boson search at
the LHC, the Higgs boson property has not yet been tightly constrained and it
is still allowed for the Higgs boson to decay invisibly to dark matter with a
sizable branching ratio. In this work, we examine the Higgs decay to neutralino
dark matter in low energy SUSY by considering three different models: the
minimal supersymmetric standard model (MSSM), the next-to-minimal
supersymmetric standard models (NMSSM) and the nearly minimal supersymmetric
standard model (nMSSM). Under current experimental constraints at 2-sigma level
(including the muon g-2 and the dark matter relic density), we scan over the
parameter space of each model. Then in the allowed parameter space we calculate
the branching ratio of the SM-like Higgs decay to neutralino dark matter and
examine its observability at the LHC by considering three production channels:
the weak boson fusion VV->h, the associated production with a Z-boson pp->hZ+X
or a pair of top quarks pp->htt_bar+X. We find that in the MSSM such a decay is
far below the detectable level; while in both the NMSSM and nMSSM the decay
branching ratio can be large enough to be observable at the LHC.Comment: Version in JHE
Effective Lagrangian approach to neutrinoless double beta decay and neutrino masses
Neutrinoless double beta () decay can in general produce
electrons of either chirality, in contrast with the minimal Standard Model (SM)
extension with only the addition of the Weinberg operator, which predicts two
left-handed electrons in the final state. We classify the lepton number
violating (LNV) effective operators with two leptons of either chirality but no
quarks, ordered according to the magnitude of their contribution to \znbb
decay. We point out that, for each of the three chirality assignments, and , there is only one LNV operator of the corresponding type
to lowest order, and these have dimensions 5, 7 and 9, respectively. Neutrino
masses are always induced by these extra operators but can be delayed to one or
two loops, depending on the number of RH leptons entering in the operator.
Then, the comparison of the decay rate and neutrino masses
should indicate the effective scenario at work, which confronted with the LHC
searches should also eventually decide on the specific model elected by nature.
We also list the SM additions generating these operators upon integration of
the heavy modes, and discuss simple realistic examples of renormalizable
theories for each case.Comment: Accepted for publication. Few misprints corrected and new references
adde
Radiative contribution to neutrino masses and mixing in SSM
In an extension of the minimal supersymmetric standard model (popularly known
as the SSM), three right handed neutrino superfields are introduced to
solve the -problem and to accommodate the non-vanishing neutrino masses
and mixing. Neutrino masses at the tree level are generated through parity
violation and seesaw mechanism. We have analyzed the full effect of one-loop
contributions to the neutrino mass matrix. We show that the current three
flavour global neutrino data can be accommodated in the SSM, for both
the tree level and one-loop corrected analyses. We find that it is relatively
easier to accommodate the normal hierarchical mass pattern compared to the
inverted hierarchical or quasi-degenerate case, when one-loop corrections are
included.Comment: 51 pages, 14 figures (58 .eps files), expanded introduction, other
minor changes, references adde
Hefty MSSM-like light Higgs in extended gauge models
It is well known that in the MSSM the lightest neutral Higgs h^0 must be, at
the tree level, lighter than the Z boson and that the loop corrections shift
this stringent upper bound up to about 130 GeV. Extending the MSSM gauge group
in a suitable way, the new Higgs sector dynamics can push the tree-level mass
of h^0 well above the tree-level MSSM limit if it couples to the new gauge
sector. This effect is further pronounced at the loop level and h^0 masses in
the 140 GeV ballpark can be reached easily. We exemplify this for a sample
setting with a low-scale U(1)_R x U(1)_B-L gauge symmetry in which neutrino
masses can be implemented via the inverse seesaw mechanism.Comment: 14 pages, 3 figures; references added, typos corrected; published
versio
Strong interface-induced spin-orbit coupling in graphene on WS2
Interfacial interactions allow the electronic properties of graphene to be
modified, as recently demonstrated by the appearance of satellite Dirac cones
in the band structure of graphene on hexagonal boron nitride (hBN) substrates.
Ongoing research strives to explore interfacial interactions in a broader class
of materials in order to engineer targeted electronic properties. Here we show
that at an interface with a tungsten disulfide (WS2) substrate, the strength of
the spin-orbit interaction (SOI) in graphene is very strongly enhanced. The
induced SOI leads to a pronounced low-temperature weak anti-localization (WAL)
effect, from which we determine the spin-relaxation time. We find that
spin-relaxation time in graphene is two-to-three orders of magnitude smaller on
WS2 than on SiO2 or hBN, and that it is comparable to the intervalley
scattering time. To interpret our findings we have performed first-principle
electronic structure calculations, which both confirm that carriers in
graphene-on-WS2 experience a strong SOI and allow us to extract a
spin-dependent low-energy effective Hamiltonian. Our analysis further shows
that the use of WS2 substrates opens a possible new route to access topological
states of matter in graphene-based systems.Comment: Originally submitted version in compliance with editorial guidelines.
Final version with expanded discussion of the relation between theory and
experiments to be published in Nature Communication
Reaction rates and transport in neutron stars
Understanding signals from neutron stars requires knowledge about the
transport inside the star. We review the transport properties and the
underlying reaction rates of dense hadronic and quark matter in the crust and
the core of neutron stars and point out open problems and future directions.Comment: 74 pages; commissioned for the book "Physics and Astrophysics of
Neutron Stars", NewCompStar COST Action MP1304; version 3: minor changes,
references updated, overview graphic added in the introduction, improvements
in Sec IV.A.
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