Search results for "Expectation value"
showing 10 items of 39 documents
Phenomenology of supersymmetry with broken R-parity
1985
Abstract In some phenomenological supersymmetric models R -parity (+1 for particles, −1 for sparticles) is spontaneously broken along with tau-lepton number L τ by a vacuum expectation value υ τ of the tau sneutrino ν τ . To avoid excess stellar energy loss through majorons, there should also be explicit L τ violation through right-handed neutrinos. To have a sufficiently light ν τ , either υ τ is very small which is unnatural and boring, and/or the Higgs mixing parameter ϵ is very small. We find that in the limit ϵ → 0: -both the forward-backward asymmetry in e + e − → τ + τ − and the τ lifetime are unchanged, -Z 0 → ggν⊥ decays are possible where ν τ is an extra neutrino, -squarks and glu…
Tau lepton mixing with charginos and its effects on chargino searches at e+e− colliders
1998
In bilinear R-Parity violating models where a term \epsilon_3L_3H_2 is introduced in the superpotential, the tau lepton can mix with charginos. We show that this mixing is fully compatible with LEP1 precision measurements of the Z\tau\tau and W\tau\nu_\tau couplings even for large values of \epsilon_3 and of the induced vacuum expectation value v_3 of the tau-sneutrino. The single production of charginos at e+e- colliders is possible in this case and we present numerical values of the cross-section at LEP1, LEP2 and an NLC. We find maximum values of 10 pb at LEP1 and 1 fb at NLC, while the corresponding values at LEP2 are too small to observe.
A Unified Approach to High Density: Pion Fluctuations in Skyrmion Matter
2003
As the first in a series of systematic work on dense hadronic matter, we study the properties of the pion in dense medium using Skyrme's effective Lagrangian as a unified theory of the hadronic interactions applicable in the large $N_c$ limit. Dense baryonic matter is described as the ground state of a skyrmion matter which appears in two differentiated phases as a function of matter density: i) at high densities as a stable cubic-centered (CC) half-skyrmion crystal; ii) at low densities as an unstable face-centered cubic (FCC) skyrmion crystal. We substitute the latter by a stable inhomogeneous phase of lumps of dense matter, which represents a naive Maxwell construction of the phase trans…
NON-PERTURBATIVE VACUUM WAVE-FUNCTIONAL AND CLOSED STRING EQUATIONS OF MOTION
1989
The anomalous conformal dependence of the vacuum wave-functional is studied in the non-perturbative regime of the closed bosonic string theory. It is shown that the vanishing of the vacuum expectation value of the stress-energy tensor trace leads to the implementation of a suitable variational condition on the wave-functional, provided that the dilaton condensate be taken as a conformal compensator for the graviton condensate of the embedding space.
Fixed versus random triangulations in 2D Regge calculus
1997
Abstract We study 2D quantum gravity on spherical topologies using the Regge calculus approach with the dl l measure. Instead of a fixed non-regular triangulation which has been used before, we study for each system size four different random triangulations, which are obtained according to the standard Voronoi-Delaunay procedure. We compare both approaches quantitatively and show that the difference in the expectation value of R2 between the fixed and the random triangulation depends on the lattice size and the surface area A. We also try again to measure the string susceptibility exponents through a finite-size scaling Ansatz in the expectation value of an added R2 interaction term in an a…
Structure of chromomagnetic fields in the glasma
2014
The initial stage of a heavy ion collision is dominated by nonperturbatively strong chromoelectric and -magnetic fields. The spatial Wilson loop provides a gauge invariant observable to probe the dynamics of the longitudinal chromomagnetic field. We discuss recent results from a real time lattice calculation of the area-dependence of the expectation value of the spatial Wilson loop. We show that at relatively early times after the collision, a universal scaling as a function of the area emerges at large distances for very different initial conditions, with a nontrivial critical exponent. A similar behavior has earlier been seen in calculations of the gluon transverse momentum spectrum, whic…
A full picture of large lepton number asymmetries of the Universe
2017
A large lepton number asymmetry of (0.1−1) at present Universe might not only be allowed but also necessary for consistency among cosmological data. We show that, if a sizeable lepton number asymmetry were produced before the electroweak phase transition, the requirement for not producing too much baryon number asymmetry through sphalerons processes, forces the high scale lepton number asymmetry to be larger than about 03. Therefore a mild entropy release causing (10-100) suppression of pre-existing particle density should take place, when the background temperature of the Universe is around T = (10−2-102) GeV for a large but experimentally consistent asymmetry to be present today. We also …
Electroweak baryogenesis at high bubble wall velocities
2020
It is widely believed that electroweak baryogenesis should be suppressed in strong phase transitions with fast-moving bubble walls, but this effect has never been quantitatively studied. We rederive fluid equations describing transport of particle asymmetries near the bubble wall without making the small-wall-velocity approximation. We show that the suppression of the baryon asymmetry is a smooth function of the wall speed and that there is no special behavior when crossing the sound speed barrier. Electroweak baryogenesis can thus be efficient also with strong detonations, generically associated with models with observably large gravitational waves. We also make a systematic and critical c…
Non-locality and causal evolution in QFT
2006
Non locality appearing in QFT during the free evolution of localized field states and in the Feynman propagator function is analyzed. It is shown to be connected to the initial non local properties present at the level of quantum states and then it does not imply a violation of Einstein's causality. Then it is investigated a simple QFT system with interaction, consisting of a classical source coupled linearly to a quantum scalar field, that is exactly solved. The expression for the time evolution of the state describing the system is given. The expectation value of any arbitrary ``good'' local observable, expressed as a function of the field operator and its space and time derivatives, is o…
Search for heavy vector-like quarks coupling to light quarks in proton–proton collisions at s=7 TeV with the ATLAS detector
2012
This letter presents a search for singly produced vector-like quarks, Q, coupling to light quarks, q. The search is sensitive to both charged current (CC) and neutral current (NC) processes, p p --> Q q --> W q q' and p p --> Q q --> Z q q' with a leptonic decay of the vector gauge boson. In 1.04/fb of data taken in 2011 by the ATLAS experiment at a center-of-mass energy sqrt(s) = 7 TeV, no evidence of such heavy vector-like quarks is observed above the expected Standard Model background. Limits on the heavy vector-like quark production cross section times branching ratio as a function of mass m_Q are obtained. For a coupling kappa_(qQ) = v/m_Q, where v is the Higgs vacuum expectation value…