2,305 research outputs found
Explaining the t tbar forward-backward asymmetry without dijet or flavor anomalies
We consider new physics explanations of the anomaly in the top quark
forward-backward asymmetry measured at the Tevatron, in the context of flavor
conserving models. The recently measured LHC dijet distributions strongly
constrain many otherwise viable models. A new scalar particle in the
antitriplet representation of flavor and color can fit the t tbar asymmetry and
cross section data at the Tevatron and avoid both low- and high-energy bounds
from flavor physics and the LHC. An s-channel resonance in uc to uc scattering
at the LHC is predicted to be not far from the current sensitivity. This model
also predicts rich top quark physics for the early LHC from decays of the new
scalar particles. Single production gives t tbar j signatures with high
transverse momentum jet, pair production leads to t tbar j j and 4 jet final
states.Comment: 7 pages, 6 figures; v2: notation clarified, references adde
Beautiful Mirrors at the LHC
We explore the "Beautiful Mirrors" model, which aims to explain the measured
value of , discrepant at the level. This scenario
introduces vector-like quarks which mix with the bottom, subtly affecting its
coupling to the . The spectrum of the new particles consists of two
bottom-like quarks and a charge -4/3 quark, all of which have electroweak
interactions with the third generation. We explore the phenomenology and
discovery reach for these new particles at the LHC, exploring single mirror
quark production modes whose rates are proportional to the same mixing
parameters which resolve the anomaly. We find that for mirror quark
masses is required to
reasonably establish the scenario and extract the relevant mixing parameters.Comment: version to be published in JHE
Probing the Tevatron t tbar asymmetry at LHC
We use an effective operator framework to study the contributions to the
Tevatron t tbar asymmetry from arbitrary vector bosons and scalars, and compare
with their effect on the t tbar tail at LHC. Our study shows, for example, that
models reproducing the t tbar asymmetry by exchange of Z' and W' bosons or
colour-triplet scalars lead to a large enhancement in the t tbar tail at LHC.
This fact can be used to exclude these models as the sole explanation for the
asymmetry, using the data already collected by CMS and ATLAS. Our analysis is
model independent in the sense that we scan over all possible extra particles
contributing to the asymmetry, and allow for general couplings. We also explore
a class of Standard Model extensions which can accommodate the Tevatron
asymmetry without contributing to the total t tbar cross section at first
order, so that the enhancement of the tail at Tevatron and LHC is moderate.Comment: LaTeX 21 pages. Added several references and comments, and an
appendix to study the validity of the effective operator approximation and
efficiency issue
LHC diphoton Higgs signal and top quark forward-backward asymmetry in quasi-inert Higgs doublet model
In the quasi-inert Higgs doublet model, we study the LHC diphoton rate for a
standard model-like Higgs boson and the top quark forward-backward asymmetry at
Tevatron. Taking into account the constraints from the vacuum stability,
unitarity, electroweak precision tests, flavor physics and the related
experimental data of top quark, we find that compared with the standard model
prediction, the diphoton rate of Higgs boson at LHC can be enhanced due to the
light charged Higgs contributions, while the measurement of the top quark
forward-backward asymmetry at Tevatron can be explained to within due
to the non-standard model neutral Higgs bosons contributions. Finally, the
correlations between the two observables are discussed.Comment: 14 pages, 5 figues. Version to appear in JHEP, some references adde
Simple models for the top asymmetry: constraints and predictions
We perform a comprehensive study of the allowed range for the Tevatron t tbar
forward-backward asymmetries in six representative new physics models: a
flavour-changing Z' boson, a scalar isodoublet, a W' boson, a heavy axigluon, a
colour-triplet and a colour-sextet scalar. We devote special attention to the
constraints from the t tbar tail at LHC on the parameter space, which will be
dramatic if the measurements agree with the SM prediction, specially for Z' and
W' bosons. We also study the predictions for the charge asymmetries at LHC and
compare several proposed definitions.Comment: LaTeX 27 pages. Version to appear in JHE
Top quark forward-backward asymmetry in R-parity violating supersymmetry
The interaction of bottom squark-mediated top quark pair production,
occurring in the R-parity violating minimal supersymmetric standard model
(MSSM), is proposed as an explanation of the anomalously large
forward-backward asymmetry (FBA) observed at the Tevatron. We find that this
model can give a good fit to top quark data, both the inclusive and invariant
mass-dependent asymmetries, while remaining consistent (at the 2-
level) with the total and differential production cross-sections. The scenario
is challenged by strong constraints from atomic parity violation (APV), but we
point out an extra diagram for the effective down quark-Z vertex, involving the
same coupling constant as required for the FBA, which tends to weaken the APV
constraint, and which can nullify it for reasonable values of the top squark
masses and mixing angle. Large contributions to flavor-changing neutral
currents can be avoided if only the third generation of sparticles is light.Comment: 24 pages, 7 figures. v3: included LHC top production cross section
data; model still consistent at 2 sigma leve
Model-Independent Searches for New Quarks at the LHC
New vector-like quarks can have sizable couplings to first generation quarks
without conflicting with current experimental constraints. The coupling with
valence quarks and unique kinematics make single production the optimal
discovery process. We perform a model-independent analysis of the discovery
reach at the Large Hadron Collider for new vector-like quarks considering
single production and subsequent decays via electroweak interactions. An early
LHC run with 7 TeV center of mass energy and 1 fb-1 of integrated luminosity
can probe heavy quark masses up to 1 TeV and can be competitive with the
Tevatron reach of 10 fb-1. The LHC with 14 TeV center of mass energy and 100
fb-1 of integrated luminosity can probe heavy quark masses up to 3.7 TeV for
order one couplings.Comment: 37 pages, 11 figures, 7 table
Light MSSM Higgs boson mass to three-loop accuracy
The light CP even Higgs boson mass, Mh, is calculated to three-loop accuracy
within the Minimal Supersymmetric Standard Model (MSSM). The result is
expressed in terms of DRbar parameters and implemented in the computer program
H3m. The calculation is based on the proper approximations and their
combination in various regions of the parameter space. The three-loop effects
to Mh are typically of the order of a few hundred MeV and opposite in sign to
the two-loop corrections. The remaining theory uncertainty due to higher order
perturbative corrections is estimated to be less than 1 GeV.Comment: 39 pages, 13 figures. v2: minor changes, typos fixe
A gallbladder tumor revealing metastatic clear cell renal carcinoma: report of case and review of literature
Discerning New Physics in Top-Antitop Production using Top Spin Observables at Hadron Colliders
Copious production of top-antitop quark pairs at hadron colliders has enabled
various probes into the properties and interactions of top quarks. Among the
various presently measured observables, the forward-backward asymmetry (FBA) in
t tbar production measured at the Tevatron significantly deviates from the
standard model predictions, and many models of new physics have been invented
to explain the puzzle. We consider the consistency of the simplified
single-resonance models containing a color octet axial-vector ("axigluon"),
color triplet or sextet weak singlet scalars, weak isodoublet scalar,
flavor-changing neutral Z', or charged W' vector boson with existing t tbar
production measurements. Among the considered models only an axigluon can
reproduce all Tevatron observables, without being in severe tension with the
recent LHC results on t tbar production cross section, charge asymmetry and
top-spin correlations. The LHC charge asymmetry measurements exclude the W' and
Z' explanations of the Tevatron FBA anomaly. On the other hand, all scalar
models predict notable deviations in several top spin observables, and the
recent top spin correlation measurement using the "helicity" spin quantization
axis by ATLAS already provides a significant constraint on possible
explanations of the Tevatron FBA anomaly. Future precise measurements of top
spin correlations and especially top polarization could differentiate between
scalar t(u)-channel models, while they are less sensitive to pure axigluon
contributions.Comment: 22 pages, 8 figures, published versio
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