10,851 research outputs found
Up Sector of Minimal Flavor Violation: Top Quark Properties and Direct D meson CP violation
Minimal Flavor Violation in the up-type quark sector leads to particularly
interesting phenomenology due to the interplay of flavor physics in the charm
sector and collider physics from flavor changing processes in the top sector.
We study the most general operators that can affect top quark properties and
meson decays in this scenario, concentrating on two CP violating operators
for detailed studies. The consequences of these effective operators on charm
and top flavor changing processes are generically small, but can be enhanced if
there exists a light flavor mediator that is a Standard Model gauge singlet
scalar and transforms under the flavor symmetry group. This flavor mediator can
satisfy the current experimental bounds with a mass as low as tens of GeV and
explain observed -meson direct CP violation. Additionally, the model
predicts a non-trivial branching fraction for a top quark decay that would
mimic a dijet resonance.Comment: 27 pages, 7 figure
Revisiting slepton pair production at the Large Hadron Collider
Motivated by the shift in experimental attention towards electroweak
supersymmetric particle production at the CERN LHC, we update in this paper our
precision predictions at next-to-leading order of perturbative QCD matched to
resummation at the next-to-leading logarithmic accuracy for direct slepton pair
production in proton-proton collisions. Simplified models, now commonly adopted
by the experimental collaborations for selectrons and smuons as well as mixing
staus, are used as benchmarks for total cross sections at achieved and future
center-of-mass energies. They are presented together with the corresponding
scale and parton density uncertainties in graphical and tabular form for future
reference. Using modern Monte Carlo techniques, we also reanalyze recent ATLAS
and CMS slepton searches in light of our precision cross sections and for
various assumptions on the decomposition of the sleptons and their neutralino
decay products.Comment: 32 pages, 10 figures, 4 tables; version accepted by JHE
CP Violation
Several pieces of direct and indirect evidence now suggest that the
Kobayashi-Maskawa mechanism plays a distinguished role for CP violation at the
electroweak scale. This talk provides a general overview of CP violation in its
various contexts, emphasizing CP violation in flavour-violating interactions,
such as due to the Kobayashi-Maskawa mechanism. I then review a few recent
theoretical developments relevant to the interpretation of CP violation.Comment: 27 pages, LaTeX; plenary talk presented at the International
Europhysics Conference on High Energy Physics, Budapest, July 2001;
manuscript has some overlap with hep-lat/020101
Rare Decays as a Probe for New Physics
We discuss the indirect search for new degrees of freedom beyond the standard
model, within flavour physics. In particular, we analyse the minimal flavour
violation hypothesis and its phenomenological implications, especially the
large-tan beta scenario in supersymmetric models, and also compare it with the
constrained minimal flavour violation scenario. Moreover, we briefly discuss
some recent progress in inclusive b to s transitions and present a status
report of the so-called K-pi puzzle.Comment: 8 pages, 6 figures, based on an invited review talk given at Beauty
2006, the 11th International Conference on B physics at Hadron Colliders,
September 2006, Oxford (England
New Physics Models of Direct CP Violation in Charm Decays
In view of the recent LHCb measurement of Delta A_CP, the difference between
the time-integrated CP asymmetries in D --> K+K- and D --> pi+pi- decays, we
perform a comparative study of the possible impact of New Physics degrees of
freedom on the direct CP asymmetries in singly Cabibbo suppressed D meson
decays. We systematically discuss scenarios with a minimal set of new degrees
of freedom that have renormalizable couplings to the SM particles and that are
heavy enough such that their effects on the D meson decays can be described by
local operators. We take into account both constraints from low energy flavor
observables, in particular D0-D0bar mixing, and from direct searches. While
models that explain the large measured value for Delta A_CP with chirally
enhanced chromomagnetic penguins are least constrained, we identify a few
viable models that contribute to the D meson decays at tree level or through
loop induced QCD penguins. We emphasize that such models motivate direct
searches at the LHC.Comment: 24 pages, 13 figures. v2: typos corrected, reference added, published
versio
Higgs Boson Production via Gluon Fusion in the Standard Model with four Generations
Higgs bosons can be produced copiously at the LHC via gluon fusion induced by
top and bottom quark loops, and can be enhanced strongly if extra heavy quarks
exist. We present results for Higgs +zero-, one- and two-jet production at the
LHC, in both the Standard Model and the 4th generation model, by evaluating the
corresponding heavy quark triangle, box and pentagon Feynman diagrams. We
compare the results by using the effective Higgs-gluon interactions in the
limit of heavy quarks with the cross sections including the full mass
dependences. NLO effects with full mass dependence are included in the
inclusive Higgs boson production rate. Our results improve the theoretical
basis for fourth generation effects on the Higgs boson search at the LHC.Comment: Published version in PR
Long-lived staus from strong production in a simplified model approach
We study the phenomenology of a supersymmetric scenario where the
next-to-lightest superparticle is the lighter stau and long-lived due to a very
weakly coupled lightest superparticle, such as the gravitino. We investigate
the LHC sensitivity and its dependence on the superparticle spectrum with an
emphasis on strong production and decay. We do not assume any high-scale model
for SUSY breaking but work along the lines of simplified models. Devising cuts
that yield a large detection efficiency in the whole parameter space, we
determine the LHC's discovery and exclusion potential. This allows us to derive
robust limits on m_stau, m_gluino, a common m_squark, and m_stop1. We briefly
discuss the prospects for observing stopped staus.Comment: 25 pages + references, 27 eps figures; v3: Matches journal version,
typo in table 1 correcte
Neutral Higgs production at proton colliders in the CP-conserving NMSSM
We discuss neutral Higgs boson production through gluon fusion and
bottom-quark annihilation in the CP-conserving -invariant
Next-to-Minimal Supersymmetric Standard Model (NMSSM) at proton colliders. For
gluon fusion we adapt known asymptotic expansions in supersymmetric particles
for the inclusion of next-to-leading order contributions of squarks and gluinos
from the Minimal Supersymmetric Standard Model (MSSM) and include electro-weak
corrections involving light quarks. Together with the resummation of higher
order sbottom contributions in the bottom-quark Yukawa coupling for both
production processes we thus present accurate cross section predictions
implemented in a new release of the code SusHi. We elaborate on the new
features of an additional SU singlet in the production of CP-even and
-odd Higgs bosons with respect to the MSSM and include a short discussion of
theory uncertainties.Comment: 33 pages, 8 figures; minor corrections, updated references, matches
published versio
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