230 research outputs found
R-parity violating resonant stop production at the Large Hadron Collider
We have investigated the resonant production of a stop at the Large Hadron
Collider, driven by baryon number violating interactions in supersymmetry. We
work in the framework of minimal supergravity models with the lightest
neutralino being the lightest supersymmetric particle which decays within the
detector. We look at various dilepton and trilepton final states, with or
without b-tags. A detailed background simulation is performed, and all possible
decay modes of the lighter stop are taken into account. We find that higher
stop masses are sometimes easier to probe, through the decay of the stop into
the third or fourth neutralino and their subsequent cascades. We also comment
on the detectability of such signals during the 7 TeV run, where, as expected,
only relatively light stops can be probed. Our conclusion is that the resonant
process may be probed, at both 10 and 14 TeV, with the R-parity violating
coupling {\lambda}"_{312} as low as 0.05, for a stop mass of about 1 TeV. The
possibility of distinguishing between resonant stop production and
pair-production is also discussed.Comment: 20 pages, 4 figures, 6 tables; Version accepted by JHE
SUSY parameter determination at the LHC using cross sections and kinematic edges
We study the determination of supersymmetric parameters at the LHC from a
global fit including cross sections and edges of kinematic distributions. For
illustration, we focus on a minimal supergravity scenario and discuss how well
it can be constrained at the LHC operating at 7 and 14 TeV collision energy,
respectively. We find that the inclusion of cross sections greatly improves the
accuracy of the SUSY parameter determination, and allows to reliably extract
model parameters even in the initial phase of LHC data taking with 7 TeV
collision energy and 1/fb integrated luminosity. Moreover, cross section
information may be essential to study more general scenarios, such as those
with non-universal gaugino masses, and distinguish them from minimal,
universal, models.Comment: 22 pages, 8 figure
Hints of R-parity violation in B decays into
In this article we show that the recently observed enhanced semi-leptonic and
leptonic decay rates of the B meson into \tau \nu modes can be explained within
the frame work of R-parity violating (RPV) MSSM. In particular, RPV
contributions involving the exchange of right-handed down-type squarks give a
universal contribution to the B+ --> \tau \nu, B --> D \tau \nu and the B -->
D* \tau \nu decays. We find that the masses and couplings that explain the
enhanced B decay rates are phenomelogically viable and the squarks can possibly
be observed at the LHC.Comment: 8 pages and 3 figures; Updated section 2 and 3, but results are
unmodifie
A Rationale for Long-lived Quarks and Leptons at the LHC: Low Energy Flavour Theory
In the framework of gauged flavour symmetries, new fermions in parity
symmetric representations of the standard model are generically needed for the
compensation of mixed anomalies. The key point is that their masses are also
protected by flavour symmetries and some of them are expected to lie way below
the flavour symmetry breaking scale(s), which has to occur many orders of
magnitude above the electroweak scale to be compatible with the available data
from flavour changing neutral currents and CP violation experiments. We argue
that, actually, some of these fermions would plausibly get masses within the
LHC range. If they are taken to be heavy quarks and leptons, in
(bi)-fundamental representations of the standard model symmetries, their
mixings with the light ones are strongly constrained to be very small by
electroweak precision data. The alternative chosen here is to exactly forbid
such mixings by breaking of flavour symmetries into an exact discrete symmetry,
the so-called proton-hexality, primarily suggested to avoid proton decay. As a
consequence of the large value needed for the flavour breaking scale, those
heavy particles are long-lived and rather appropriate for the current and
future searches at the LHC for quasi-stable hadrons and leptons. In fact, the
LHC experiments have already started to look for them.Comment: 10 pages, 1 figur
Composite Leptoquarks at the LHC
If electroweak symmetry breaking arises via strongly-coupled physics, the
observed suppression of flavour-changing processes suggests that fermion masses
should arise via mixing of elementary fermions with composite fermions of the
strong sector. The strong sector then carries colour charge, and may contain
composite leptoquark states, arising either as TeV scale resonances, or even as
light, pseudo-Nambu-Goldstone bosons. The latter, since they are coupled to
colour, get a mass of the order of several hundred GeV, beyond the reach of
current searches at the Tevatron. The same generic mechanism that suppresses
flavour-changing processes suppresses leptoquark-mediated rare processes,
making it conceivable that the many stringent constraints may be evaded. The
leptoquarks couple predominantly to third-generation quarks and leptons, and
the prospects for discovery at LHC appear to be good. As an illustration, a
model based on the Pati-Salam symmetry is described, and its embedding in
models with a larger symmetry incorporating unification of gauge couplings,
which provide additional motivation for leptoquark states at or below the TeV
scale, is discussed.Comment: 10 pp, version to appear in JHE
A new CP violating observable for the LHC
We study a new type of CP violating observable that arises in three body
decays that are dominated by an intermediate resonance. If two interfering
diagrams exist with different orderings of final state particles, the required
CP-even phase arises due to the different virtualities of the resonance in each
of the two diagrams. This method can be an important tool for accessing new CP
phases at the LHC and future colliders.Comment: 22 pages, v2: discussion of charged particle decays and a few
references added v3: typos corrected, matches published versio
Goldstini Can Give the Higgs a Boost
Supersymmetric collider phenomenology depends crucially on whether the
lightest observable-sector supersymmetric particle (LOSP) decays, and if so,
what the LOSP decay products are. For instance, in SUSY models where the
gravitino is lighter than the LOSP, the LOSP decays to its superpartner and a
longitudinal gravitino via supercurrent couplings. In this paper, we show that
LOSP decays can be substantially modified when there are multiple sectors that
break supersymmetry, where in addition to the gravitino there are light uneaten
goldstini. As a particularly striking example, a bino-like LOSP can have a near
100% branching fraction to a higgs boson and an uneaten goldstino, even if the
LOSP has negligible higgsino fraction. This occurs because the uneaten
goldstino is unconstrained by the supercurrent, allowing additional operators
to mediate LOSP decay. These operators can be enhanced in the presence of an R
symmetry, leading to copious boosted higgs production in SUSY cascade decays.Comment: 30 pages, 12 figures; v2: title change, clarifications added, version
to appear in JHE
Dynamical R-parity Breaking at the LHC
In a class of extensions of the minimal supersymmetric standard model with
(B-L)/left-right symmetry that explains the neutrino masses, breaking R-parity
symmetry is an essential and dynamical requirement for successful gauge
symmetry breaking. Two consequences of these models are: (i) a new kind of
R-parity breaking interaction that protects proton stability but adds new
contributions to neutrinoless double beta decay and (ii) an upper bound on the
extra gauge and parity symmetry breaking scale which is within the large hadron
collider (LHC) energy range. We point out that an important prediction of such
theories is a potentially large mixing between the right-handed charged lepton
() and the superpartner of the right-handed gauge boson (), which leads to a brand new class of R-parity violating interactions of
type and \widetilde{d^c}^\dagger\u^c
e^c. We analyze the relevant constraints on the sparticle mass spectrum and
the LHC signatures for the case with smuon/stau NLSP and gravitino LSP. We note
the "smoking gun" signals for such models to be lepton flavor/number violating
processes: (or ) and
(or ) without
significant missing energy. The predicted multi-lepton final states and the
flavor structure make the model be distinguishable even in the early running of
the LHC.Comment: 30 pages, 13 figures, 6 tables, reference adde
Limit Cycles in Four Dimensions
We present an example of a limit cycle, i.e., a recurrent flow-line of the
beta-function vector field, in a unitary four-dimensional gauge theory. We thus
prove that beta functions of four-dimensional gauge theories do not produce
gradient flows. The limit cycle is established in perturbation theory with a
three-loop calculation which we describe in detail.Comment: 12 pages, 1 figure. Significant revision of the interpretation of our
result. Improved description of three-loop calculatio
The Full Two-Loop R-parity Violating Renormalization Group Equations for All Minimal Supersymmetric Standard Model Couplings
We present the full two-loop -functions for the minimal supersymmetric
standard model couplings, extended to include R-parity violating couplings
through explicit R-parity violation
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