12,182 research outputs found
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
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