Momentum Space Regularizations and the Indeterminacy in the Schwinger Model

We revisited the problem of the presence of finite indeterminacies that appear in the calculations of a Quantum Field Theory. We investigate the occurrence of undetermined mathematical quantities in the evaluation of the Schwinger model in several regularization scenarios. We show that the undetermined character of the divergent part of the vacuum polarization tensor of the model, introduced as an {\it ansatz} in previous works, can be obtained mathematically if one introduces a set of two parameters in the evaluation of these quantities. The formal mathematical properties of this tensor and their violations are discussed. The analysis is carried out in both analytical and sharp cutoff regularization procedures. We also show how the Pauli Villars regularization scheme eliminates the indeterminacy, giving a gauge invariant result in the vector Schwinger model.Comment: 10 pages, no figure

pMSSM Benchmark Models for Snowmass 2013

We present several benchmark points in the phenomenological Minimal Supersymmetric Standard Model (pMSSM). We select these models as experimentally well-motivated examples of the MSSM which predict the observed Higgs mass and dark matter relic density while evading the current LHC searches. We also use benchmarks to generate spokes in parameter space by scaling the mass parameters in a manner which keeps the Higgs mass and relic density approximately constant.Comment: 10 pages, 6 figure

Making the small oblique parameters large

We compute the oblique parameters, including the three new parameters $V$, $W$ and $X$ introduced recently by the Montreal group, for the case of one scalar multiplet of arbitrary weak isospin $J$ and weak hypercharge $Y$. We show that, when the masses of the heaviest and lightest components of the multiplet remain constant, but $J$ increases, the oblique parameter $U$ and the three new oblique parameters increase like $J^3$, while $T$ only increases like $J$. For large multiplets with masses not much higher than $m_Z$, the oblique parameters $U$ and $V$ may become much larger than $T$ and $S$.Comment: 9 pages, standard LATEX, 3 figures available from the authors, report CMU-HEP93-17 and DOE-ER/40682-4

Entanglement renormalization and gauge symmetry

A lattice gauge theory is described by a redundantly large vector space that is subject to local constraints, and can be regarded as the low energy limit of an extended lattice model with a local symmetry. We propose a numerical coarse-graining scheme to produce low energy, effective descriptions of lattice models with a local symmetry, such that the local symmetry is exactly preserved during coarse-graining. Our approach results in a variational ansatz for the ground state(s) and low energy excitations of such models and, by extension, of lattice gauge theories. This ansatz incorporates the local symmetry in its structure, and exploits it to obtain a significant reduction of computational costs. We test the approach in the context of the toric code with a magnetic field, equivalent to Z2 lattice gauge theory, for lattices with up to 16 x 16 sites (16^2 x 2 = 512 spins) on a torus. We reproduce the well-known ground state phase diagram of the model, consisting of a deconfined and spin polarized phases separated by a continuous quantum phase transition, and obtain accurate estimates of energy gaps, ground state fidelities, Wilson loops, and several other quantities.Comment: reviewed version as published in PRB; this version includes a new section about the accuracy of the results several corrections and added citation

Hadronic production of light color-triplet Higgs bosons: an alternative signature for GUT

The conventional signature for grand unified theories (GUT) is the proton decay. Recently, some models in extra dimensions or with specific discrete symmetries, which aim at solving the doublet-triplet problem, allow the color-triplet in the TeV mass region by suppressing the Yukawa couplings of the triplets to matter fermions. We study the hadronic production and detection of these TeV colored Higgs bosons as an alternative signature for GUT, which would behave like massive stable charged particles in particle detectors producing a striking signature of a charged track in the central tracking system and being ionized in the outer muon chamber. We found that the LHC is sensitive to a colored Higgs boson up to about 1.5 TeV. If the color-triplets are stable in cosmological time scale, they may constitute an interesting fraction of the dark matter.Comment: We added the description of a model by Goldberger et al.-- a 5D SU(5) SUSY model in a slice of AdS space with special boundary conditions to suppress proton decay. The color-triplet also has a TeV mas

Electron's anomalous magnetic moment effects on electron-hydrogen elastic collisions in the presence of a circularly polarized laser field

The effect of the electron's anomalous magnetic moment on the relativistic electronic dressing for the process of electron-hydrogen atom elastic collisions is investigated. We consider a laser field with circular polarization and various electric field strengths. The Dirac-Volkov states taking into account this anomaly are used to describe the process in the first order of perturbation theory. The correlation between the terms coming from this anomaly and the electric field strength gives rise to new results, namely the strong dependence of the spinor part of the differential cross section (DCS) with respect to these terms. A detailed study has been devoted to the non relativistic regime as well as the moderate relativistic regime. Some aspects of this dependence as well as the dynamical behavior of the DCS in the relativistic regime have been addressed.Comment: 1 File Revtex + 14 figures ep

Constraints on R-parity violating couplings from LEP/SLD hadronic observables

We analyze the one loop corrections to hadronic Z decays in an R-parity violating extension to the Minimal Supersymmetric Standard Model (MSSM). Performing a global fit to all the hadronic observables at the Z-peak, we obtain stringent constraints on the R-violating couplings constants lambda' and lambda''. As a result of the strong constraints from the b asymmetry parameters A_b and A_FB(b), we find that the couplings lambda'{i31}, lambda'{i32}, and lambda''{321} are ruled out at the 1 sigma level, and that lambda'{i33} and lambda''{33i} are ruled out at the 2 sigma level. We also obtain Bayesian confidence limits for the R-violating couplings.Comment: 30 pages, 19 postscript figures, REVTeX, new section 8 on Bayesian confidence limits adde

Radiation reaction and gravitational waves in the effective field theory approach

We compute the contribution to the Lagrangian from the leading order (2.5 post-Newtonian) radiation reaction and the quadrupolar gravitational waves emitted from a binary system using the effective field theory (EFT) approach of Goldberger and Rothstein. We use an initial value formulation of the underlying (quantum) framework to implement retarded boundary conditions and describe these real-time dissipative processes. We also demonstrate why the usual scattering formalism of quantum field theory inadequately accounts for these. The methods discussed here should be useful for deriving real-time quantities (including radiation reaction forces and gravitational wave emission) and hereditary terms in the post-Newtonian approximation (including memory, tail and other causal, history-dependent integrals) within the EFT approach. We also provide a consistent formulation of the radiation sector in the equivalent effective field theory approach of Kol and Smolkin.Comment: 23 pages, 8 figure

Gravitational Wilson Loop and Large Scale Curvature

In a quantum theory of gravity the gravitational Wilson loop, defined as a suitable quantum average of a parallel transport operator around a large near-planar loop, provides important information about the large-scale curvature properties of the geometry. Here we shows that such properties can be systematically computed in the strong coupling limit of lattice regularized quantum gravity, by performing a local average over rotations, using an assumed near-uniform measure in group space. We then relate the resulting quantum averages to an expected semi-classical form valid for macroscopic observers, which leads to an identification of the gravitational correlation length appearing in the Wilson loop with an observed large-scale curvature. Our results suggest that strongly coupled gravity leads to a positively curved (De Sitter-like) quantum ground state, implying a positive effective cosmological constant at large distances.Comment: 22 pages, 6 figure

NLO Corrections to lepton pair production beyond the Standard Model at hadron colliders

We consider lepton pair production at a hadron collider in a class of effective theories with the relevant operators being four-fermion contact interaction. Despite the nonrenormalizable nature of the interaction, we explicitly demonstrate that calculating QCD corrections is both possible and meaningful. Calculating the corrections for various differential distributions, we show that these can be substantial and significantly different from those within the SM. Furthermore, the corrections have a very distinctive flavour dependence. And finally, the scale dependence of the cross sections are greatly reduced once the NLO corrections are taken into account.Comment: 23 pages, 14 figures, few typos corrected, written in JHEP styl