[Show abstract][Hide abstract] ABSTRACT: We discuss the possibility that flavor hierarchies arise from the electroweak
scale in a two Higgs doublet model, in which the two Higgs doublets jointly act
as the flavon. Quark masses and mixing angles are explained by effective Yukawa
couplings, generated by higher dimensional operators involving quarks and Higgs
doublets. Modified Higgs couplings yield important effects on the production
cross sections and decay rates of the light Standard Model like Higgs. In
addition, flavor changing neutral currents arise at tree-level and lead to
strong constraints from meson-antimeson mixing. Remarkably, flavor constraints
turn out to prefer a region in parameter space that is in excellent agreement
with the one preferred by recent Higgs precision measurements at the Large
Hadron Collider (LHC). Direct searches for extra scalars at the LHC lead to
further constraints. Precise predictions for the production and decay modes of
the additional Higgs bosons are derived, and we present benchmark scenarios for
searches at the LHC Run II. Flavor breaking at the electroweak scale as well as
strong coupling effects demand a UV completion at the scale of a few TeV,
possibly within the reach of the LHC.
[Show abstract][Hide abstract] ABSTRACT: Precision measurements of the Higgs boson properties at the LHC provide relevant constraints on possible weak-scale extensions of the Standard Model (SM). In the context of the Minimal Supersymmetric Standard Model (MSSM) these constraints seem to suggest that all the additional, non-SM-like Higgs bosons should be heavy, with masses larger than about 400 GeV. This article shows that such results do not hold when the theory approaches the conditions for "alignment independent of decoupling", where the lightest CP-even Higgs boson has SM-like tree-level couplings to fermions and gauge bosons, independently of the non-standard Higgs boson masses. The combination of current bounds from direct Higgs boson searches at the LHC, along with the alignment conditions, have a significant impact on the allowed MSSM parameter space yielding light additional Higgs bosons. In particular, after ensuring the correct mass for the lightest CP-even Higgs boson, we find that precision measurements and direct searches are complementary, and may soon be able to probe the region of non-SM-like Higgs boson with masses below the top quark pair mass threshold of 350 GeV and low to moderate values of tanβ.
Physical Review D 10/2014; 91(3). DOI:10.1103/PhysRevD.91.035003 · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Warped extra-dimension models in which the Higgs boson is allowed to propagate in the bulk of a compact AdS5 space are conjectured to be dual to models featuring a partially composite Higgs boson. They offer a framework with which to investigate the implications of changing the scaling dimension of the Higgs operator, which can be used to reduce the constraints from electroweak precision data. In the context of such models, we calculate the cross section for Higgs production in gluon fusion and the H → γγ decay rate and show that they are finite (at one-loop order) as a consequence of gauge invariance. The extended scalar sector comprising the Kaluza-Klein excitations of the Standard Model scalars is constructed in detail. The largest effects are due to virtual KK fermions, whose contributions to the cross section and decay rate introduce a quadratic sensitivity to the maximum allowed value y
∗ of the random complex entries of the 5D anarchic Yukawa matrices. We find an enhancement of the gluon-fusion cross section and a reduction of the H →γγ rate as well as of the tree-level Higgs couplings to fermions and electroweak gauge bosons. We perform a detailed study of the correlated signal strengths for different production mechanisms and decay channels as functions of y
∗, the mass scale of Kaluza-Klein resonances and the scaling dimension of the composite Higgs operator.
Journal of High Energy Physics 08/2014; 2015(1). DOI:10.1007/JHEP01(2015)060 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We study classically scale invariant models in which the Standard Model Higgs
mass term is replaced in the Lagrangian by a Higgs portal coupling to a complex
scalar field of a dark sector. We focus on models that are weakly coupled with
the quartic scalar couplings nearly vanishing at the Planck scale. The dark
sector contains fermions and scalars charged under dark SU(2) x U(1) gauge
interactions. Radiative breaking of the dark gauge group triggers electroweak
symmetry breaking through the Higgs portal coupling. Requiring both a Higgs
boson mass of 125.5 GeV and stability of the Higgs potential up to the Planck
scale implies that the radiative breaking of the dark gauge group occurs at the
TeV scale. We present a particular model which features a long-range abelian
dark force. The dominant dark matter component is neutral dark fermions, with
the correct thermal relic abundance, and in reach of future direct detection
experiments. The model also has lighter stable dark fermions charged under the
dark force, with observable effects on galactic-scale structure. Collider
signatures include a dark sector scalar boson with mass < 250 GeV that decays
through mixing with the Higgs boson, and can be detected at the LHC. The Higgs
boson, as well as the new scalar, may have significant invisible decays into
dark sector particles.
Journal of High Energy Physics 08/2014; 2015(1). DOI:10.1007/JHEP01(2015)032 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We consider composite Higgs models where the Higgs is a pseudo-Nambu
Goldstone boson arising from the spontaneous breaking of an approximate global
symmetry by some underlying strong dynamics. We focus on the SO(5) -> SO(4)
symmetry breaking pattern, assuming the partial compositeness paradigm. We
study the consequences on Higgs physics of the fermionic representations
produced by the strong dynamics, that mix with the Standard Model (SM) degrees
of freedom. We consider models based on the lowest-dimensional representations
of SO(5) that allow for the custodial protection of the Z -> b b coupling, i.e.
the 5, 10 and 14. We find a generic suppression of the gluon fusion process,
while the Higgs branching fractions can be enhanced or suppressed compared to
the SM. Interestingly, a precise measurement of the Higgs boson couplings can
distinguish between different realizations in the fermionic sector, thus
providing crucial information about the nature of the UV dynamics.
Journal of High Energy Physics 02/2014; 2014(6). DOI:10.1007/JHEP06(2014)159 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In models with an extended Higgs sector there exists an alignment limit, in
which the lightest CP-even Higgs boson mimics the Standard Model Higgs. The
alignment limit is commonly associated with the decoupling limit, where all
non-standard scalars are significantly heavier than the $Z$ boson. However,
alignment can occur irrespective of the mass scale of the rest of the Higgs
sector. In this work we discuss the general conditions that lead to "alignment
without decoupling", therefore allowing for the existence of additional
non-standard Higgs bosons at the weak scale. The values of $\tan\beta$ for
which this happens are derived in terms of the effective Higgs quartic
couplings in general two-Higgs-doublet models as well as in supersymmetric
theories, including the MSSM and the NMSSM. Moreover, we study the information
encoded in the variations of the SM Higgs-fermion couplings to explore regions
in the $m_A - \tan\beta$ parameter space.
Journal of High Energy Physics 10/2013; 2014(4). DOI:10.1007/JHEP04(2014)015 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We study extensions of the standard model by one generation of vector-like
leptons with non-standard hypercharges, which allow for a sizable modification
of the h -> gamma gamma decay rate for new lepton masses in the 300 GeV - 1 TeV
range. We analyze vaccum stability implications for different hypercharges.
Effects in h -> Z gamma are typically much smaller than in h -> gamma gamma,
but distinct among the considered hypercharge assignments. Non-standard
hypercharges constrain or entirely forbid possible mixing operators with
standard model leptons. As a consequence, the leading contributions to the
experimentally strongly constrained electric dipole moments of standard model
fermions are only generated at the two loop level by the new CP violating
sources of the considered setups. We derive the bounds from dipole moments,
electro-weak precision observables and lepton flavor violating processes, and
discuss their implications. Finally, we examine the production and decay
channels of the vector-like leptons at the LHC, and find that signatures with
multiple light leptons or taus are already probing interesting regions of
parameter space.
Journal of High Energy Physics 08/2013; 2014(1). DOI:10.1007/JHEP01(2014)060 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The ATLAS and CMS experiments have recently announced the discovery of a
Higgs-like resonance with mass close to 125 GeV. Overall, the data is
consistent with a Standard Model (SM)-like Higgs boson. Such a particle
may arise in the minimal super-symmetric extension of the SM with
average stop masses of the order of the TeV scale and a sizable stop
mixing parameter. In this article we discuss properties of the SM-like
Higgs production and decay rates induced by the possible presence of
light staus and light stops. Light staus can affect the decay rate of
the Higgs into di-photons and, in the case of sizable left-right mixing,
induce an enhancement in this production channel up to ~ 50% of the
Standard Model rate. Light stops may induce sizable modifications of the
Higgs gluon fusion production rate and correlated modifications to the
Higgs diphoton decay. Departures from SM values of the bottom-quark and
tau-lepton couplings to the Higgs can be obtained due to Higgs mixing
effects triggered by light third generation scalar superpartners. We
describe the phenomenological implications of light staus on searches
for light stops and non-standard Higgs bosons. Finally, we discuss the
current status of the search for light staus produced in association
with sneutrinos, in final states containing a W gauge boson and a pair
of τ s.
Journal of High Energy Physics 08/2013; 2013(8):087-. DOI:10.1007/JHEP08(2013)087 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Part 2 of "Project X: Accelerator Reference Design, Physics Opportunities,
Broader Impacts". In this Part, we outline the particle-physics program that
can be achieved with Project X, a staged superconducting linac for
intensity-frontier particle physics. Topics include neutrino physics, kaon
physics, muon physics, electric dipole moments, neutron-antineutron
oscillations, new light particles, hadron structure, hadron spectroscopy, and
lattice-QCD calculations. Part 1 is available as arXiv:1306.5022
[physics.acc-ph] and Part 3 is available as arXiv:1306.5024 [physics.acc-ph].
[Show abstract][Hide abstract] ABSTRACT: Current Higgs data at the Large Hadron Collider is compatible with a SM
signal at the 2$\sigma$ level, but the central value of the signal strength in
the diphoton channel is enhanced with respect to the SM expectation. If the
enhancement resides in the diphoton partial decay width, the data could be
accommodated in the Minimally Supersymmetric Standard Model (MSSM) with highly
mixed light staus. We revisit the issue of vacuum instability induced by large
mixing in the stau sector, including effects of a radiatively-corrected tau
Yukawa coupling. Further, we emphasize the importance of taking into account
the $\tan\beta$ dependence in the stability bound. While the metastability of
the Universe constrains the possible enhancement in the Higgs to diphoton decay
width in the light stau scenario, an increase of the order of 50% can be
achieved in the region of large $\tan\beta$. Larger enhancements may be
obtained, but would require values of $\tan\beta$ associated with
non-perturbative values of the tau Yukawa coupling at scales below the GUT
scale, thereby implying the presence of new physics beyond the MSSM.
Journal of High Energy Physics 11/2012; 2013(2). DOI:10.1007/JHEP02(2013)114 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We study the minimal supersymmetric standard model (MSSM) with minimal flavor
violation (MFV), imposing constraints from flavor physics observables and MSSM
Higgs searches, in light of the recent discovery of a 125 GeV Higgs boson by
ATLAS and CMS. We analyze the electroweak vacuum stability conditions to
further restrict the MSSM parameter space. In addition, a connection to
ultraviolet physics is shown via an implementation of renormalization group
running, which determines the TeV-scale spectrum from a small set of minimal
supergravity parameters. Finally, we investigate the impact from dark matter
direct detection searches. Our work highlights the complementarity of collider,
flavor and dark matter probes in exploring the MSSM, and shows that even in a
MFV framework, flavor observables constrain the MSSM parameter space well
beyond the current reach of direct SUSY particle searches.
Journal of High Energy Physics 11/2012; 2013(1). DOI:10.1007/JHEP01(2013)160 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Electroweak baryogenesis is an attractive scenario for the generation of the
baryon asymmetry of the universe as its realization depends on the presence at
the weak scale of new particles which may be searched for at high energy
colliders. In the MSSM it may only be realized in the presence of light stops,
and with moderate or small mixing between the left- and right-handed
components. Consistency with the observed Higgs mass around 125 GeV demands the
heavier stop mass to be much larger than the weak scale. Moreover the lighter
stop leads to an increase of the gluon-gluon fusion Higgs production cross
section which seems to be in contradiction with indications from current LHC
data. We show that this tension may be considerably relaxed in the presence of
a light neutralino with a mass lower than about 60 GeV, satisfying all present
experimental constraints. In such a case the Higgs may have a significant
invisible decay width and the stop decays through a three or four body decay
channel, including a bottom quark and the lightest neutralino in the final
state. All these properties make this scenario testable at a high luminosity
LHC.
Journal of High Energy Physics 07/2012; 2013(2). DOI:10.1007/JHEP02(2013)001 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Motivated by recent results from Higgs searches at the Large Hadron Collider,
we consider possibilities to enhance the diphoton decay width of the Higgs
boson over the Standard Model expectation, without modifying either its
production rate or the partial widths in the WW and ZZ channels. Studying
effects of new charged scalars, fermions and vector bosons, we find that
significant variations in the diphoton width may be possible if the new
particles have light masses of the order of a few hundred GeV and sizeable
couplings to the Higgs boson. Such couplings could arise naturally if there is
large mass mixing between two charged particles that is induced by the Higgs
vacuum expectation value. In addition, there is generically also a shift in the
Z + Gamma partial width, which in the case of new vector bosons tends to be of
similar magnitude as the shift in the diphoton partial width, but smaller in
other cases. Therefore simultaneous measurements in these two channels could
reveal properties of new charged particles at the electroweak scale.
Journal of High Energy Physics 06/2012; 2012(8). DOI:10.1007/JHEP08(2012)060 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The LHC has started to constrain supersymmetry-breaking parameters by setting
bounds on possible colored particles at the weak scale. Moreover, constraints
from Higgs physics, flavor physics, the anomalous magnetic moment of the muon,
as well as from searches at LEP and the Tevatron have set additional bounds on
these parameters. Renormalization Group Invariants (RGIs) provide a very useful
way of representing the allowed parameter space by making direct connection
with the values of these parameters at the messenger scale. Using a general
approach, based on the pMSSM parametrization of the soft supersymmetry-breaking
parameters, we analyze the current experimental constraints to determine the
probability distributions for the RGIs. As examples of their application, we
use these distributions to analyze the question of Gaugino Mass Unification and
to probabilistically determine the parameters of General and Minimal Gauge
Mediation with arbitrary Higgs mass parameters at the Messenger Scale.
[Show abstract][Hide abstract] ABSTRACT: Recently, an excess of events consistent with a Higgs boson with mass of about 125 GeV was reported by the CMS and ATLAS experiments. This Higgs boson mass is consistent with the values that may be obtained in minimal supersymmetric extensions of the Standard Model (SM), with both stop masses less than a TeV and large mixing. The apparently enhanced photon production rate associated with this potential Higgs signal may be the result of light staus with large mixing. Large stau mixing and large coupling of the staus to the SM-like Higgs boson may be obtained for large values of tan β and moderate to large values of the Higgsino mass parameter, μ. We study the phenomenological properties of this scenario, including precision electroweak data, the muon anomalous magnetic moment, Dark Matter, and the evolution of the soft supersymmetry-breaking parameters to high energies. We also analyze the possible collider signatures of light third generation sleptons and demonstrate that it is possible to find evidence of their production at the 8 TeV and the 14 TeV LHC. The most promising channel is stau and tau sneutrino associated production, with the sneutrino decaying into a W boson plus a light stau.
Journal of High Energy Physics 05/2012; 2012(7). DOI:10.1007/JHEP07(2012)175 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Measurements of the Higgs-boson production cross section at the LHC are an
important tool for studying electroweak symmetry breaking at the quantum level,
since the main production mechanism gg-->h is loop-suppressed in the Standard
Model (SM). Higgs production in extra-dimensional extensions of the SM is
sensitive to the Kaluza-Klein (KK) excitations of the quarks, which can be
exchanged as virtual particles in the loop. In the context of the minimal
Randall-Sundrum (RS) model with bulk fields and a brane-localized Higgs sector,
we derive closed analytical expressions for the gluon-gluon fusion process,
finding that the effect of the infinite tower of virtual KK states can be
described in terms of a simple function of the fundamental (5D) Yukawa
matrices. Given a specific RS model, this will allow one to easily constrain
the parameter space, once a Higgs signal has been established. We explain that
discrepancies between existing calculations of Higgs production in RS models
are related to the non-commutativity of two limits: taking the number of KK
states to infinity and removing the regulator on the Higgs-boson profile, which
is required in an intermediate step to make the relevant overlap integrals well
defined. Even though the one-loop gg-->h amplitude is finite in RS scenarios
with a brane-localized Higgs sector, it is important to introduce a consistent
ultraviolet regulator in order to obtain the correct result.
Journal of High Energy Physics 03/2012; 2012(8). DOI:10.1007/JHEP08(2012)156 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In a variety of well motivated models, such as two Higgs Doublet Models
(2HDMs) and the Minimal Supersymmetric Standard Model (MSSM), there are neutral
Higgs bosons that have significantly enhanced couplings to b-quarks and tau
leptons in comparison to those of the SM Higgs. These so called non-standard
Higgs bosons could be copiously produced at the LHC in association with b
quarks, and subsequently decay into b-quark pairs. However, this production
channel suffers from large irreducible QCD backgrounds. We propose a new search
strategy for non-standard neutral Higgs bosons at the 7 TeV LHC in the 3b's
final state topology. We perform a simulation of the signal and backgrounds,
using state of the art tools and methods for different sets of selection cuts,
and conclude that neutral Higgs bosons with couplings to b-quarks of about 0.3
or larger, and masses up to 400 GeV, could be seen with a luminosity of 30
fb^{-1}. In the case of the MSSM we also discuss the complementarity between
the 3b channel and the inclusive tau pair channel in exploring the
supersymmetric parameter space.
Journal of High Energy Physics 03/2012; 2012(7). DOI:10.1007/JHEP07(2012)091 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We consider the possibility of a Standard Model (SM)-like Higgs in the context of the Minimal Supersymmetric Standard Model (MSSM), with a mass of about 125 GeV and with a production times decay rate into two photons which is similar or somewhat larger than the SM one. The relatively large value of the SM-like Higgs mass demands stops in the several hundred GeV mass range with somewhat large mixing, or a large hierarchy between the two stop masses in the case that one of the two stops is light. We find that, in general, if the heaviest stop mass is smaller than a few TeV, the rate of gluon fusion production of Higgs bosons decaying into two photons tends to be somewhat suppressed with respect to the SM one in this region of parameters. However, we show that an enhancement of the photon decay rate may be obtained for light third generation sleptons with large mixing, which can be naturally obtained for large values of tan β and sizable values of the Higgsino mass parameter.
Journal of High Energy Physics 03/2012; 2012(3). DOI:10.1007/JHEP03(2012)014 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We consider the Higgs sector in extensions of the minimal supersymmetric standard model by higher-dimension operators in the superpotential and the Kähler potential, in the context of Higgs searches at the LHC 7 TeV run. Such an effective field theory approach, also referred to as BMSSM, allows for a model-independent description that may correspond to the combined effects of additional supersymmetric sectors, such as heavy singlets, triplets or gauge bosons, in which the supersymmetry-breaking mass splittings can be treated as a perturbation. We consider the current LHC dataset, based on about 1–2 fb-1 of data to set exclusion limits on a large class of BMSSM models. We also present projections for integrated luminosities of 5 and 15 fb-1, assuming that the ATLAS and CMS collaborations will combine their results in each channel. Our study shows that the majority of the parameter space will be probed at the 2σ level with 15 fb-1 of data. A nonobservation of a Higgs boson with about 10 fb-1 of data will point towards a Higgs SUSY spectrum with intermediate tanβ (≈a few to10) and a light SM-like Higgs with somewhat enhanced couplings to bottom and tau pairs. We define a number of BMSSM benchmark scenarios and analyze the possible exclusion/discovery channels and the projected required luminosity to probe them. We also discuss the results of the effective field theory framework for two specific models, one with a singlet superfield and one with SU(2)L triplets.