871 research outputs found
LHC Discovery Potential for Non-Standard Higgs Bosons in the 3b Channel
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.Comment: 14 pages, 3 figures, 4 tables, references added, published versio
Spin- and energy relaxation of hot electrons at GaAs surfaces
The mechanisms for spin relaxation in semiconductors are reviewed, and the
mechanism prevalent in p-doped semiconductors, namely spin relaxation due to
the electron-hole exchange interaction, is presented in some depth. It is shown
that the solution of Boltzmann-type kinetic equations allows one to obtain
quantitative results for spin relaxation in semiconductors that go beyond the
original Bir-Aronov-Pikus relaxation-rate approximation. Experimental results
using surface sensitive two-photon photoemission techniques show that the spin
relaxation-time of electrons in p-doped GaAs at a semiconductor/metal surface
is several times longer than the corresponding bulk spin relaxation-times. A
theoretical explanation of these results in terms of the reduced density of
holes in the band-bending region at the surface is presented.Comment: 33 pages, 12 figures; earlier submission replaced by corrected and
expanded version; eps figures now included in the tex
Hadronic production of bottom-squark pairs with electroweak contributions
We present the complete computation of the tree-level and the next-to-leading
order electroweak contributions to bottom-squark pair production at the LHC.
The computation is performed within the minimal supersymmetric extension of the
Standard Model. We discuss the numerical impact of these contributions in
several supersymmetric scenarios.Comment: 33 pages, v2: preprint numbers correcte
Relic densities including Sommerfeld enhancements in the MSSM
We have developed a general formalism to compute Sommerfeld enhancement (SE)
factors for a multi-state system of fermions, in all possible spin
configurations and with generic long-range interactions. We show how to include
such SE effects in an accurate calculation of the thermal relic density for
WIMP dark matter candidates. We apply the method to the MSSM and perform a
numerical study of the relic abundance of neutralinos with arbitrary
composition and including the SE due to the exchange of the W and Z bosons,
photons and Higgses. We find that the relic density can be suppressed by a
factor of a few in a seizable region of the parameter space, mostly for
Wino-like neutralino with mass of a few TeV, and up to an order of magnitude
close to a resonance.Comment: 23 pages, 7 figures; table 1 corrected and rearranged, numerical
results practically unchanged, matches published versio
Gauge-independent renormalization in the 2HDM
We present a consistent renormalization scheme for the CP-conserving
Two-Higgs-Doublet Model based on renormalization of the mixing
angles and the soft--symmetry-breaking scale in the Higgs sector.
This scheme requires to treat tadpoles fully consistently in all steps of the
calculation in order to provide gauge-independent -matrix elements. We show
how bare physical parameters have to be defined and verify the gauge
independence of physical quantities by explicit calculations in a general
-gauge. The procedure is straightforward and applicable to other
models with extended Higgs sectors. In contrast to the proposed scheme, the
renormalization of the mixing angles combined with popular
on-shell renormalization schemes gives rise to gauge-dependent results already
at the one-loop level. We present explicit results for electroweak NLO
corrections to selected processes in the appropriately renormalized
Two-Higgs-Doublet Model and in particular discuss their scale dependence.Comment: 52 pages, PDFLaTeX, PDF figures, JHEP version with Eq. (5.23)
correcte
Theoretical Constraints on the Higgs Effective Couplings
We derive constraints on the sign of couplings in an effective Higgs
Lagrangian using prime principles such as the naturalness principle, global
symmetries, and unitarity. Specifically, we study four dimension-six operators,
O_H, O_y, O_g, and O_gamma, which contribute to the production and decay of the
Higgs boson at the Large Hadron Collider (LHC), among other things. Assuming
the Higgs is a fundamental scalar, we find: 1) the coefficient of O_H is
positive except when there are triplet scalars, resulting in a reduction in the
Higgs on-shell coupling from their standard model (SM) expectations if no other
operators contribute, 2) the linear combination of O_H and O_y controlling the
overall Higgs coupling to fermion is always reduced, 3) the sign of O_g induced
by a new colored fermion is such that it interferes destructively with the SM
top contribution in the gluon fusion production of the Higgs, if the new
fermion cancels the top quadratic divergence in the Higgs mass, and 4) the
correlation between naturalness and the sign of O_gamma is similar to that of
O_g, when there is a new set of heavy electroweak gauge bosons. Next
considering a composite scalar for the Higgs, we find the reduction in the
on-shell Higgs couplings persists. If further assuming a collective breaking
mechanism as in little Higgs theories, the coefficient of O_H remains positive
even in the presence of triplet scalars. In the end, we conclude that the gluon
fusion production of the Higgs boson is reduced from the SM rate in all
composite Higgs models. Our study suggests a wealth of information could be
revealed by precise measurements of the Higgs couplings, providing strong
motivations for both improving on measurements at the LHC and building a
precision machine such as the linear collider.Comment: 37 pages, one figure; v2: improved discussion on dispersion relation
and other minor modifications; version accepted for publication
The HERMIT in the Tree
This paper describes our experience using the HERMIT tool- kit to apply well-known transformations to the internal core language of the Glasgow Haskell Compiler. HERMIT provides several mechanisms to support writing general-purpose transformations: a domain-specific language for strategic programming specialized to GHC's core language, a library of primitive rewrites, and a shell-style{based scripting language for interactive and batch usage. There are many program transformation techniques that have been described in the literature but have not been mechanized and made available inside GHC - either because they are too specialized to include in a general-purpose compiler, or because the developers' interest is in theory rather than implementation. The mechanization process can often reveal pragmatic obstacles that are glossed over in pen-and-paper proofs; understanding and removing these obstacles is our concern. Using HERMIT, we implement eleven examples of three program transformations, report on our experience, and describe improvements made in the process
Higgs Low-Energy Theorem (and its corrections) in Composite Models
The Higgs low-energy theorem gives a simple and elegant way to estimate the
couplings of the Higgs boson to massless gluons and photons induced by loops of
heavy particles. We extend this theorem to take into account possible nonlinear
Higgs interactions resulting from a strong dynamics at the origin of the
breaking of the electroweak symmetry. We show that, while it approximates with
an accuracy of order a few percents single Higgs production, it receives
corrections of order 50% for double Higgs production. A full one-loop
computation of the gg->hh cross section is explicitly performed in MCHM5, the
minimal composite Higgs model based on the SO(5)/SO(4) coset with the Standard
Model fermions embedded into the fundamental representation of SO(5). In
particular we take into account the contributions of all fermionic resonances,
which give sizeable (negative) corrections to the result obtained considering
only the Higgs nonlinearities. Constraints from electroweak precision and
flavor data on the top partners are analyzed in detail, as well as direct
searches at the LHC for these new fermions called to play a crucial role in the
electroweak symmetry breaking dynamics.Comment: 30 pages + appendices and references, 12 figures. v2: discussion of
flavor constraints improved; references added; electroweak fit updated,
results unchanged. Matches published versio
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
Broadening INPP5E phenotypic spectrum: detection of rare variants in syndromic and non-syndromic IRD
Pathogenic variants in INPP5E cause Joubert syndrome (JBTS), a ciliopathy with retinal involvement. However, despite sporadic cases in large cohort sequencing studies, a clear association with non-syndromic inherited retinal degenerations (IRDs) has not been made. We validate this association by reporting 16 non-syndromic IRD patients from ten families with bi-allelic mutations in INPP5E. Additional two patients showed early onset IRD with limited JBTS features. Detailed phenotypic description for all probands is presented. We report 14 rare INPP5E variants, 12 of which have not been reported in previous studies. We present tertiary protein modeling and analyze all INPP5E variants for deleteriousness and phenotypic correlation. We observe that the combined impact of INPP5E variants in JBTS and non-syndromic IRD patients does not reveal a clear genotype–phenotype correlation, suggesting the involvement of genetic modifiers. Our study cements the wide phenotypic spectrum of INPP5E disease, adding proof that sequence defects in this gene can lead to early-onset non-syndromic IRD
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