Search results for "Symmetry Breaking"
showing 10 items of 319 documents
One-loop calculation of the oblique S parameter in higgsless electroweak models
2012
We present a one-loop calculation of the oblique S parameter within Higgsless models of electroweak symmetry breaking and analyze the phenomenological implications of the available electroweak precision data. We use the most general effective Lagrangian with at most two derivatives, implementing the chiral symmetry breaking SU(2)_L x SU(2)_R -> SU(2)_{L+R} with Goldstones, gauge bosons and one multiplet of vector and axial-vector massive resonance states. Using the dispersive representation of Peskin and Takeuchi and imposing the short-distance constraints dictated by the operator product expansion, we obtain S at the NLO in terms of a few resonance parameters. In asymptotically-free gauge …
Left-right symmetry breaking in NJL approach
1995
We study left-right symmetric models which contain only fermion and gauge boson fields and no elementary scalars. The Higgs bosons are generated dynamically through a set of gauge- and parity-invariant 4-fermion operators. It is shown that in a model with a composite bi-doublet and two triplet scalars there is no parity breaking at low energies, whereas in the model with two doublets instead of two triplets parity is broken automatically regardless of the choice of the parameters of the model. For phenomenologically allowed values of the right-handed scale a tumbling symmetry breaking mechanism is realized in which parity breaking at a high scale $\mu_R$ propagates down and eventually cause…
Supersymmetry with spontaneous R-parity breaking in Z0 decays: the case of an additional Z
1991
Single production of SUSY particles in the decays of the Z0 may proceed with large rates in models with spontaneously broken R-parity. We focus on the case where there is a lepton number symmetry as part of the gauge group. In the simplest of such models there is a single additional neutral gauge boson and the strength of Rp-violating interactions is related with that of the new gauge force. We study the phenomenological implications of the model for Z0 decays, including the study of the rates for single chargino production in Z0 decays, i.e. Z0→ξ±τ±, as well as for the so-called Zen events, and find that they may be measurable at LEP. The first process, characteristics of spontaneously bro…
Fading of symmetry nonrestoration at finite temperature
1998
The fate of symmetries at high temperature determines the dynamics of the very early universe. It is conceivable that temperature effects favor symmetry breaking instead of restoration. Concerning global symmetries, the non-linear sigma model is analyzed in detail. For spontaneously broken gauge symmetries, we propose the gauge boson magnetic mass as a ``flag'' for symmetry (non)-restoration. We consider several cases: the standard model with one and two Higgs doublets in the perturbative regime, and the case of a strongly interacting Higgs sector. The latter is done in a model independent way with the tools provided by chiral Lagrangians. Our results clearly point towards restoration, a pa…
Search for diphoton events with large missing transverse momentum in 1 fb−1 of 7 TeV proton–proton collision data with the ATLAS detector
2012
A search for diphoton events with large missing transverse momentum has been performed using 1.07 fb(-1) of proton-proton collision data at root s = 7 TeV recorded with the ATLAS detector. No excess of events was observed above the Standard Model prediction and 95% Confidence Level (CL) upper limits are set on the production cross section for new physics. The limits depend on each model parameter space and vary as follows: sigma < (22-129) fb in the context of a generalised model of gauge-mediated supersymmetry breaking (GGM) with a bino-like lightest neutralino, sigma < (27-91) fb in the context of a minimal model of gauge-mediated supersymmetry breaking (SPS8), and sigma < (15-27) fb in t…
WEAK INTERACTIONS, SYMMETRIES
1981
Abstract The Standard ideas about the breaking of symmetries, through the mechanism of generation mixing, are discussed. New results and proposals looking for discrete space-time symmetry violation as well as flavour-number violation are reported. The use of weak-interaction processes as a tool for both the study of the structure of the currents and for nuclear-structure problems is emphasized.
Isospin-invariant Skyrme energy-density-functional approach with axial symmetry
2014
We develop the isospin-invariant Skyrme-EDF method by considering local densities in all possible isospin channels and proton-neutron (p-n) mixing terms as mandated by the isospin symmetry. The EDF employed has the most general form that depends quadratically on the isoscalar and isovector densities. We test and benchmark the resulting p-n EDF approach, and study the general properties of the new scheme by means of the cranking in the isospin space. We extend the existing axial DFT solver HFBTHO to the case of isospin-invariant EDF approach with all possible p-n mixing terms. Explicit expressions have been derived for all the densities and potentials that appear in the isospin representatio…
Soft leptogenesis in the inverse seesaw model
2006
We consider leptogenesis induced by soft supersymmetry breaking terms ("soft leptogenesis"), in the context of the inverse seesaw mechanism. In this model there are lepton number (L) conserving and L-violating soft supersymmetry-breaking B-terms involving the singlet sneutrinos which, together with the -- generically small-- L-violating parameter responsible of the neutrino mass, give a small mass splitting between the four singlet sneutrino states of a single generation. In combination with the trilinear soft supersymmetry breaking terms they also provide new CP violating phases needed to generate a lepton asymmetry in the singlet sneutrino decays. We obtain that in this scenario the lepto…
extended MSSM
2012
We investigate the perturbative regime of the Minimal Supersymmetric Con- formal Technicolor and show that it allows for a stable vacuum correctly breaking the electroweak symmetry. We nd that the particle spectrum is richer than the MSSM one since it features several new particles stemming out from the new N = 4 sector of the theory. The parameter space of the new theory is reduced imposing naturalness of the cou- plings and soft supersymmetry breaking masses, perturbativity of the model at the EW scale as well as phenomenological constraints. By studying the RGEs at two loops we nd that the Yukawa couplings of the heavy fermionic states
Search for supersymmetry in di-photon final states at s=1.96 TeV
2008
We report results of a search for supersymmetry (SUSY) with gauge-mediated symmetry breaking in di-photon events collected by the DO experiment at the Fermilab Tevatron Collider in 2002-2006. In 1.1 fb(-1) of data, we find no significant excess beyond the background expected from the standard model and set the most stringent lower limits to date for a standard benchmark model on the lightest neutralino and chargino masses of 125 GeV and 229 GeV, respectively, at 95% confidence.