95,447 research outputs found
A Machine Checked Model of Idempotent MGU Axioms For Lists of Equational Constraints
We present formalized proofs verifying that the first-order unification
algorithm defined over lists of satisfiable constraints generates a most
general unifier (MGU), which also happens to be idempotent. All of our proofs
have been formalized in the Coq theorem prover. Our proofs show that finite
maps produced by the unification algorithm provide a model of the axioms
characterizing idempotent MGUs of lists of constraints. The axioms that serve
as the basis for our verification are derived from a standard set by extending
them to lists of constraints. For us, constraints are equalities between terms
in the language of simple types. Substitutions are formally modeled as finite
maps using the Coq library Coq.FSets.FMapInterface. Coq's method of functional
induction is the main proof technique used in proving many of the axioms.Comment: In Proceedings UNIF 2010, arXiv:1012.455
Neutralino Dark Matter, b-tau Yukawa Unification and Non-Universal Sfermion Masses
We study the implications of minimal non-Universal Boundary Conditions in the
sfermion Soft SUSY Breaking (SSB) masses of mSUGRA. We impose asymptotic b-tau
Yukawa coupling Unification and we resort to a parameterization of the
deviation from Universality in the SSB motivated by the multiplet structure of
SU(5) GUT. A set of cosmo-phenomenological constraints, including the recent
results from WMAP, determines the allowed parameter space of the models under
consideration. We highlight a new coannihilation corridor where
neutralino-sbottom and neutralino-tau sneutrino-stau coannihilations
significantly contribute to the reduction of the neutralino relic density.Comment: 38 pages, 27 Figures, Latex; Version accepted for publication in PR
The pMSSM Interpretation of LHC Results Using Rernormalization Group Invariants
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.Comment: 38 pages, 10 figure
CAutoCSD-evolutionary search and optimisation enabled computer automated control system design
This paper attempts to set a unified scene for various linear time-invariant (LTI) control system design schemes, by transforming the existing concept of 'Computer-Aided Control System Design' (CACSD) to the novel 'Computer-Automated Control System Design' (CAutoCSD). The first step towards this goal is to accommodate, under practical constraints, various design objectives that are desirable in both time and frequency-domains. Such performance-prioritised unification is aimed to relieve practising engineers from having to select a particular control scheme and from sacrificing certain performance goals resulting from pre-committing to the adopted scheme. With the recent progress in evolutionary computing based extra-numeric, multi-criterion search and optimisation techniques, such unification of LTI control schemes becomes feasible, analytically and practically, and the resultant designs can be creative. The techniques developed are applied to, and illustrated by, three design problems. The unified approach automatically provides an integrator for zero-steady state error in velocity control of a DC motor, meets multiple objectives in designing an LTI controller for a non-minimum phase plant and offers a high-performing LTI controller network for a nonlinear chemical process
Leptophobic U(1)'s and the R_b - R_c Crisis
In this paper, we investigate the possibility of explaining both the R_b
excess and the R_c deficit reported by the LEP experiments through Z-Z' mixing
effects. We have constructed a set of models consistent with a restrictive set
of principles: unification of the Standard Model (SM) gauge couplings, vector-
like additional matter, and couplings which are both generation-independent and
leptophobic. These models are anomaly-free, perturbative up to the GUT scale,
and contain realistic mass spectra. Out of this class of models, we find three
explicit realizations which fit the LEP data to a far better extent than the
unmodified SM or MSSM and satisfy all other phenomenological constraints which
we have investigated. One realization, the \eta-model coming from E_6, is
particularly attractive, arising naturally from geometrical compactifications
of heterotic string theory. This conclusion depends crucially on the inclusion
of a U(1) kinetic mixing term, whose value is correctly predicted by
renormalization group running in the E_6 model given one discrete choice of
spectra.Comment: LaTeX, 26 pages, 5 embedded EPSF figures. Version to be published in
Phys. Rev.
Indirect signals from light neutralinos in supersymmetric models without gaugino mass unification
We examine indirect signals produced by neutralino self-annihilations, in the
galactic halo or inside celestial bodies, in the frame of an effective MSSM
model without gaugino-mass unification at a grand unification scale. We compare
our theoretical predictions with current experimental data of gamma-rays and
antiprotons in space and of upgoing muons at neutrino telescopes. Results are
presented for a wide range of the neutralino mass, though our discussions are
focused on light neutralinos. We find that only the antiproton signal is
potentially able to set constraints on very low-mass neutralinos, below 20 GeV.
The gamma-ray signal, both from the galactic center and from high galactic
latitudes, requires significantly steep profiles or substantial clumpiness in
order to reach detectable levels. The up-going muon signal is largely below
experimental sensitivities for the neutrino flux coming from the Sun; for the
flux from the Earth an improvement of about one order of magnitude in
experimental sensitivities (with a low energy threshold) can make accessible
neutralino masses close to O, Si and Mg nuclei masses, for which resonant
capture is operative.Comment: 17 pages, 1 tables and 5 figures, typeset with ReVTeX4. The paper may
also be found at http://www.to.infn.it/~fornengo/papers/indirect04.ps.gz or
through http://www.astroparticle.to.infn.it/. Limit from BR(Bs--> mu+ mu-)
adde
Naturalness and the Status of Supersymmetry
For decades, the unnaturalness of the weak scale has been the dominant
problem motivating new particle physics, and weak-scale supersymmetry has been
the dominant proposed solution. This paradigm is now being challenged by a
wealth of experimental data. In this review, we begin by recalling the
theoretical motivations for weak-scale supersymmetry, including the gauge
hierarchy problem, grand unification, and WIMP dark matter, and their
implications for superpartner masses. These are set against the leading
constraints on supersymmetry from collider searches, the Higgs boson mass, and
low-energy constraints on flavor and CP violation. We then critically examine
attempts to quantify naturalness in supersymmetry, stressing the many
subjective choices that impact the results both quantitatively and
qualitatively. Finally, we survey various proposals for natural supersymmetric
models, including effective supersymmetry, focus point supersymmetry,
compressed supersymmetry, and R-parity-violating supersymmetry, and summarize
their key features, current status, and implications for future experiments.Comment: 38 pages, to appear in Annual Review of Nuclear and Particle Science;
v2: fixed typos, updated Higgs results, added references and a parable,
published versio
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