Little Higgs Phenomenology

Recently a new class of models has emerged that addresses the naturalness problem of a light Higgs boson. In these ''little Higgs'' models, the Standard Model Higgs boson is a pseudo-Nambu-Goldstone boson of an approximate global symmetry. The Higgs boson acquires mass radiatively only through ''collective breaking'' of the global symmetry, so that more than one interaction is required to give the Higgs a mass. This protects the Higgs mass from receiving quadratically divergent radiative corrections at one-loop. These models contain new vector bosons, fermions and scalars at the TeV scale that cancel the quadratic divergences in the Higgs mass due to the Standard Model gauge, top quark, and Higgs boson loops. In this talk I review the phenomenology of the little Higgs models, focusing on collider signatures and electroweak precision constraints.Comment: 3 pages, 2 figures, talk given at EPS 2003, Aachen, Germany, July 200

Dark matter annihilation through a lepton-specific Higgs boson

It was recently argued by Hooper and Goodenough [arXiv:1010.2752] that the excess gamma ray emission from within 1-2 degrees of the galactic center can be well-described by annihilation of ~8 GeV dark matter particles into tau pairs. I show that such a dark matter signal can be obtained naturally in the lepton-specific two-Higgs-doublet model extended by a stable singlet scalar dark matter candidate. The favored parameter region prefers a light Higgs state (below 200 GeV) with enhanced couplings to leptons and sizable invisible branching fraction. Part of the favored region leads to invisible decays of both of the CP-even neutral Higgs states.Comment: 15 pages, no figures. V2: references added, fine-tuning discussion improved, submitted to PRD. V3: added Sec. 6 on direct detection prospects and associated refs, version accepted by PR

TASI 2013 lectures on Higgs physics within and beyond the Standard Model

These lectures start with a detailed pedagogical introduction to electroweak symmetry breaking in the Standard Model, including gauge boson and fermion mass generation and the resulting predictions for Higgs boson interactions. I then survey Higgs boson decays and production mechanisms at hadron and e+e- colliders. I finish with two case studies of Higgs physics beyond the Standard Model: two-Higgs-doublet models, which I use to illustrate the concept of minimal flavor violation, and models with isospin-triplet scalar(s), which I use to illustrate the concept of custodial symmetry.Comment: 48 pages, 25 figures, comments welcome. v2: fixed nonstandard convention for SU(2) generators T+/T- (changes in Eqs. 46, 47, 51, 163, 164, and 165

Active lamp pulse driver circuit

A flashlamp drive circuit is described which uses an unsaturated transistor as a current mode switch to periodically subject a partially ionized gaseous laser excitation flashlamp to a stable, rectangular pulse of current from an incomplete discharge of an energy storage capacitor. A monostable multivibrator sets the pulse interval, initiating the pulse in response to a flash command by providing a reference voltage to a non-inverting terminal of a base drive amplifier; a tap on an emitter resistor provides a feedback signal sensitive to the current amplitude to an inverting terminal of amplifier, thereby controlling the pulse amplitude. The circuit drives the flashlamp to provide a squarewave current flashlamp discharge

Magnetic properties of the Anderson model: a local moment approach

We develop a local moment approach to static properties of the symmetric Anderson model in the presence of a magnetic field, focussing in particular on the strong coupling Kondo regime. The approach is innately simple and physically transparent; but is found to give good agreement, for essentially all field strengths, with exact results for the Wilson ratio, impurity magnetization, spin susceptibility and related properties.Comment: 7 pages, 3 postscript figues. Latex 2e using the epl.cls Europhysics Letters macro packag

Self-consistent theory of many-body localisation in a quantum spin chain with long-range interactions

Many-body localisation is studied in a disordered quantum spin-1/2 chain with long-ranged power-law interactions, and distinct power-law exponents for interactions between longitudinal and transverse spin components. Using a self-consistent mean-field theory centring on the local propagator in Fock space and its associated self-energy, a localisation phase diagram is obtained as a function of the power-law exponents and the disorder strength of the random fields acting on longitudinal spin-components. Analytical results are corroborated using the well-studied and complementary numerical diagnostics of level statistics, entanglement entropy, and participation entropy, obtained via exact diagonalisation. We find that increasing the range of interactions between transverse spin components hinders localisation and enhances the critical disorder strength. In marked contrast, increasing the interaction range between longitudinal spin components is found to enhance localisation and lower the critical disorder.Comment: 30 pages, 4 figure