45 research outputs found
Two Simple W' Models for the Early LHC
W' gauge bosons are good candidates for early LHC discovery. We define two
reference models, one containing a W'_R and one containing a W'_L, which may
serve as ``simplified models'' for presenting experimental results of W'
searches at the LHC. We present the Tevatron bounds on each model and compute
the constraints from precision electroweak observables. We find that indirect
low-energy constraints on the W'_L are quite strong. However, for a W'_R
coupling to right-handed fermions there exists a sizeable region in parameter
space beyond the bounds from the Tevatron and low-energy precision measurements
where even 50 inverse picobarns of integrated LHC luminosity are sufficient to
discover the W'_R. The most promising final states are two leptons and two
jets, or one lepton recoiling against a ``neutrino jet''. A neutrino jet is a
collimated object consisting of a hard lepton and two jets arising from the
decay of a highly boosted massive neutrino.Comment: 20 pages, 8 figures. v2: references adde
5D UED: Flat and Flavorless
5D UED is not automatically minimally flavor violating. This is due to flavor
asymmetric counter-terms required on the branes. Additionally, there are likely
to be higher dimensional operators which directly contribute to flavor
observables. We document a mostly unsuccessful attempt at utilizing
localization in a flat extra dimension to resolve these flavor constraints
while maintaining KK-parity as a good quantum number. It is unsuccessful
insofar as we seem to be forced to add brane operators in such a way as to
precisely mimic the effects of a double throat warped extra dimension. In the
course of our efforts, we encounter and present solutions to a problem common
to many extra dimensional models in which fields are "doubly localized:"
ultra-light modes. Under scrutiny, this issue seems tied to an intrinsic
tension between maintaining Kaluza-Klein parity and resolving mass hierarchies
via localization.Comment: 27 pages, 6 figure
Composite Higgs Search at the LHC
The Higgs boson production cross-sections and decay rates depend, within the
Standard Model (SM), on a single unknown parameter, the Higgs mass. In
composite Higgs models where the Higgs boson emerges as a pseudo-Goldstone
boson from a strongly-interacting sector, additional parameters control the
Higgs properties which then deviate from the SM ones. These deviations modify
the LEP and Tevatron exclusion bounds and significantly affect the searches for
the Higgs boson at the LHC. In some cases, all the Higgs couplings are reduced,
which results in deterioration of the Higgs searches but the deviations of the
Higgs couplings can also allow for an enhancement of the gluon-fusion
production channel, leading to higher statistical significances. The search in
the H to gamma gamma channel can also be substantially improved due to an
enhancement of the branching fraction for the decay of the Higgs boson into a
pair of photons.Comment: 32 pages, 16 figure
Sparticle mass spectra from SU(5) SUSY GUT models with Yukawa coupling unification
Supersymmetric grand unified models based on the gauge group SU(5) often
require in addition to gauge coupling unification, the unification of b-quark
and -lepton Yukawa couplings. We examine SU(5) SUSY GUT parameter space
under the condition of Yukawa coupling unification using 2-loop MSSM
RGEs including full 1-loop threshold effects. The Yukawa-unified solutions
break down into two classes. Solutions with low tan\beta ~3-11 are
characterized by gluino mass ~1-4 TeV and squark mass ~1-5 TeV. Many of these
solutions would be beyond LHC reach, although they contain a light Higgs scalar
with mass <123 GeV and so may be excluded should the LHC Higgs hint persist.
The second class of solutions occurs at large tan\beta ~35-60, and are a subset
of unified solutions. Constraining only unification to ~5%
favors a rather light gluino with mass ~0.5-2 TeV, which should ultimately be
accessible to LHC searches. While our unified solutions can be
consistent with a picture of neutralino-only cold dark matter, invoking
additional moduli or Peccei-Quinn superfields can allow for all of our
Yukawa-unified solutions to be consistent with the measured dark matter
abundance.Comment: 19 pages, 5 figures, 1 table, PDFLate
General Gauge and Anomaly Mediated Supersymmetry Breaking in Grand Unified Theories with Vector-Like Particles
In Grand Unified Theories (GUTs) from orbifold and various string
constructions the generic vector-like particles do not need to form complete
SU(5) or SO(10) representations. To realize them concretely, we present
orbifold SU(5) models, orbifold SO(10) models where the gauge symmetry can be
broken down to flipped SU(5) X U(1)_X or Pati-Salam SU(4)_C X SU(2)_L X SU(2)_R
gauge symmetries, and F-theory SU(5) models. Interestingly, these vector-like
particles can be at the TeV-scale so that the lightest CP-even Higgs boson mass
can be lifted, or play the messenger fields in the Gauge Mediated Supersymmetry
Breaking (GMSB). Considering GMSB, ultraviolet insensitive Anomaly Mediated
Supersymmetry Breaking (AMSB), and the deflected AMSB, we study the general
gaugino mass relations and their indices, which are valid from the GUT scale to
the electroweak scale at one loop, in the SU(5) models, the flipped SU(5) X
U(1)_X models, and the Pati-Salam SU(4)_C X SU(2)_L X SU(2)_R models. In the
deflected AMSB, we also define the new indices for the gaugino mass relations,
and calculate them as well. Using these gaugino mass relations and their
indices, we may probe the messenger fields at intermediate scale in the GMSB
and deflected AMSB, determine the supersymmetry breaking mediation mechanisms,
and distinguish the four-dimensional GUTs, orbifold GUTs, and F-theory GUTs.Comment: RevTex4, 45 pages, 15 tables, version to appear in JHE
Yukawa-unified natural supersymmetry
Previous work on t-b-\tau Yukawa-unified supersymmetry, as expected from SUSY
GUT theories based on the gauge group SO(10), tended to have exceedingly large
electroweak fine-tuning (EWFT). Here, we examine supersymmetric models where we
simultaneously require low EWFT ("natural SUSY") and a high degree of Yukawa
coupling unification, along with a light Higgs scalar with m_h\sim125 GeV. As
Yukawa unification requires large tan\beta\sim50, while EWFT requires rather
light third generation squarks and low \mu\sim100-250 GeV, B-physics
constraints from BR(B\to X_s\gamma) and BR(B_s\to \mu+\mu-) can be severe. We
are able to find models with EWFT \Delta\lesssim 50-100 (better than 1-2% EWFT)
and with Yukawa unification as low as R_yuk\sim1.3 (30% unification) if
B-physics constraints are imposed. This may be improved to R_yuk\sim1.2 if
additional small flavor violating terms conspire to improve accord with
B-constraints. We present several Yukawa-unified natural SUSY (YUNS) benchmark
points. LHC searches will be able to access gluinos in the lower 1-2 TeV
portion of their predicted mass range although much of YUNS parameter space may
lie beyond LHC14 reach. If heavy Higgs bosons can be accessed at a high rate,
then the rare H, A\to \mu+\mu- decay might allow a determination of
tan\beta\sim50 as predicted by YUNS models. Finally, the predicted light
higgsinos should be accessible to a linear e+e- collider with \sqrt{s}\sim0.5
TeV.Comment: 18 pages, 7 figures, pdflatex; 3 references adde
An Alternative Yukawa Unified SUSY Scenario
Supersymmetric SO(10) Grand Unified Theories with Yukawa unification
represent an appealing possibility for physics beyond the Standard Model.
However Yukawa unification is made difficult by large threshold corrections to
the bottom mass. Generally one is led to consider models where the sfermion
masses are large in order to suppress these corrections. Here we present
another possibility, in which the top and bottom GUT scale Yukawa couplings are
equal to a component of the charged lepton Yukawa matrix at the GUT scale in a
basis where this matrix is not diagonal. Physically, this weak eigenstate
Yukawa unification scenario corresponds to the case where the charged leptons
that are in the 16 of SO(10) containing the top and bottom quarks mix with
their counterparts in another SO(10) multiplet. Diagonalizing the resulting
Yukawa matrix introduces mixings in the neutrino sector. Specifically we find
that for a large region of parameter space with relatively light sparticles,
and which has not been ruled out by current LHC or other data, the mixing
induced in the neutrino sector is such that , in
agreement with data. The phenomenological implications are analyzed in some
detail.Comment: 32 pages, 22 Figure
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
New Constraints (and Motivations) for Abelian Gauge Bosons in the MeV-TeV Mass Range
We survey the phenomenological constraints on abelian gauge bosons having
masses in the MeV to multi-GeV mass range (using precision electroweak
measurements, neutrino-electron and neutrino-nucleon scattering, electron and
muon anomalous magnetic moments, upsilon decay, beam dump experiments, atomic
parity violation, low-energy neutron scattering and primordial
nucleosynthesis). We compute their implications for the three parameters that
in general describe the low-energy properties of such bosons: their mass and
their two possible types of dimensionless couplings (direct couplings to
ordinary fermions and kinetic mixing with Standard Model hypercharge). We argue
that gauge bosons with very small couplings to ordinary fermions in this mass
range are natural in string compactifications and are likely to be generic in
theories for which the gravity scale is systematically smaller than the Planck
mass - such as in extra-dimensional models - because of the necessity to
suppress proton decay. Furthermore, because its couplings are weak, in the
low-energy theory relevant to experiments at and below TeV scales the charge
gauged by the new boson can appear to be broken, both by classical effects and
by anomalies. In particular, if the new gauge charge appears to be anomalous,
anomaly cancellation does not also require the introduction of new light
fermions in the low-energy theory. Furthermore, the charge can appear to be
conserved in the low-energy theory, despite the corresponding gauge boson
having a mass. Our results reduce to those of other authors in the special
cases where there is no kinetic mixing or there is no direct coupling to
ordinary fermions, such as for recently proposed dark-matter scenarios.Comment: 49 pages + appendix, 21 figures. This is the final version which
appears in JHE
Sizeable \theta_13 from the Charged Lepton Sector in SU(5), (Tri-)Bimaximal Neutrino Mixing and Dirac CP Violation
The recent results from T2K and MINOS experiments point towards a relatively
large value of the reactor angle \theta_13 in the lepton sector. In this paper
we show how a large \theta_13 can arise from the charged lepton sector alone in
the context of an SU(5) GUT. In such a scenario (tri-)bimaximal mixing in the
neutrino sector is still a viable possibility. We also analyse the general
implications of the considered scenario for the searches of CP violation in
neutrino oscillations.Comment: 19 pages, 3 figures; version to be published in JHE