1,821 research outputs found

### Little Higgs Review

Recently there has been renewed interest in the possibility that the Higgs
particle of the Standard Model is a pseudo-Nambu-Goldstone boson. This
development was spurred by the observation that if certain global symmetries
are broken only by the interplay between two or more coupling constants, then
the Higgs mass-squared is free from quadratic divergences at one loop. This
"collective symmetry" breaking is the essential ingredient in little Higgs
theories, which are weakly coupled extensions of the Standard Model with little
or no fine tuning, describing physics up to an energy scale ~10 TeV. Here we
give a pedagogical introduction to little Higgs theories. We review their
structure and phenomenology, focusing mainly on the SU(3) theory, the Minimal
Moose, and the Littlest Higgs as concrete examples.Comment: To appear in Annual Review of Nuclear and Particle Science; contains
TASI'05 Little Higgs lecture notes, 44 page

### Four-nucleon contact interactions from holographic QCD

We calculate the low energy constants of four-nucleon interactions in an
effective chiral Lagrangian in holographic QCD. We start with a D4-D8 model to
obtain meson-nucleon interactions and then integrate out massive mesons to
obtain the four-nucleon interactions in 4D. We end up with two low energy
constants at the leading order and seven of them at the next leading order,
which is consistent with the effective chiral Lagrangian. The values of the low
energy constants are evaluated with the first five Kaluza-Klein resonances.Comment: 28 page

### One Loop Renormalization of the Littlest Higgs Model

In Little Higgs models a collective symmetry prevents the Higgs from
acquiring a quadratically divergent mass at one loop. This collective symmetry
is broken by weakly gauged interactions. Terms, like Yukawa couplings, that
display collective symmetry in the bare Lagrangian are generically renormalized
into a sum of terms that do not respect the collective symmetry except possibly
at one renormalization point where the couplings are related so that the
symmetry is restored. We study here the one loop renormalization of a
prototypical example, the Littlest Higgs Model. Some features of the
renormalization of this model are novel, unfamiliar form similar chiral
Lagrangian studies.Comment: 23 pages, 17 eps figure

### Axion-Higgs Unification

In theories with no fundamental scalars, one gauge group can become strong at
a large scale Lambda and spontaneously break a global symmetry, producing the
Higgs and the axion as composite pseudo-Nambu-Goldstone bosons. We show how
KSVZ and DFSZ axion models can be naturally realised. The assumption Lambda
around 10^{11} GeV is phenomenologically favoured because: a) The axion solves
the QCD theta problem and provides the observed DM abundance; b) The observed
Higgs mass is generated via RGE effects from a small Higgs quartic coupling at
the compositeness scale, provided that the Higgs mass term is fine-tuned to be
of electroweak size; c) Lepton, quark as well as neutrino masses can be
obtained from four-fermion operators at the compositeness scale. d) The extra
fermions can unify the gauge couplings.Comment: 19 pages. Refs. added and eq. 3.6 fixe

### Tests of the Gravitational Inverse-Square Law

We review recent experimental tests of the gravitational inverse-square law
and the wide variety of theoretical considerations that suggest the law may
break down in experimentally accessible regions.Comment: 81 pages, 10 figures, submitted by permission of the Annual Review of
Nuclear and Particle Science. Final version of this material is scheduled to
appear in the Annual Review of Nuclear and Particle Science Vol. 53, to be
published in December 2003 by Annual Reviews, http://AnnualReviews.or

### Bounding wide composite vector resonances at the LHC

In composite Higgs models (CHMs), electroweak precision data generically push
colourless composite vector resonances to a regime where they dominantly decay
into pairs of light top partners. This greatly attenuates their traces in
canonical collider searches, tailored for narrow resonances promptly decaying
into Standard Model final states. By reinterpreting the CMS same-sign dilepton
(SS2$\ell$) analysis at the Large Hadron Collider (LHC), originally designed to
search for top partners with electric charge $5/3$, we demonstrate its
significant coverage over this kinematical regime. We also show the reach of
the 13 TeV run of the LHC, with various integrated luminosity options, for a
possible upgrade of the SS2$\ell$ search. The top sector of CHMs is found to be
more fine-tuned in the presence of colourless composite resonances in the few
TeV range.Comment: 9 pages, 5 figures. Minor corrections for publication in JHE

### Discovering the composite Higgs through the decay of a heavy fermion

A possible composite nature of the Higgs could be revealed at the early stage
of the LHC, by analyzing the channels where the Higgs is produced from the
decay of a heavy fermion. The Higgs production from a singly-produced heavy
bottom, in particular, proves to be a promising channel. For a value \lambda=3
of the Higgs coupling to a heavy bottom, for example, we find that, considering
a 125 GeV Higgs which decays into a pair of b-quarks, a discovery is possible
at the 8 TeV LHC with 30 fb^{-1} if the heavy bottom is lighter than roughly
530 GeV (while an observation is possible for heavy bottom masses up to 650
GeV). Such a relatively light heavy bottom is realistic in composite Higgs
models of the type considered and, up to now, experimentally allowed. At
\sqrt{s}=14 TeV the LHC sensitivity on the channel increases significantly.
With \lambda=3 a discovery can occur, with 100 fb^{-1}, for heavy bottom masses
up to 1040 GeV. In the case the heavy bottom was as light as 500 GeV, the 14
TeV LHC would be sensitive to the measure of the \lambda\ coupling in basically
the full range \lambda>1 predicted by the theory.Comment: 25 pp. v2: Minor changes. v3: Version accepted for publication in
JHEP. v4: typos fixe

### Spin 3/2 Baryons and Form Factors in AdS/QCD

We study the 5D Rarita-Schwinger fields to describe spin 3/2 baryons in
AdS/QCD. We calculate the spectrum of spin 3/2 baryons (Delta resonances) and
their form factors, together with meson-baryon couplings from AdS/QCD. The
transition form-factors between Delta and nucleon are evaluated. Both pion and
rho meson couplings have the same origin in the bulk and hence unified. The
numerical values for the meson-baryon transition couplings are consistent with
the values obtained from other methods. We also predict the numerical values of
some new couplings associated with Delta resonances.Comment: 29 pages, 6 figure

### Model-Independent Bounds on a Light Higgs

We present up-to-date constraints on a generic Higgs parameter space. An
accurate assessment of these exclusions must take into account statistical, and
potentially signal, fluctuations in the data currently taken at the LHC. For
this, we have constructed a straightforward statistical method for making full
use of the data that is publicly available. We show that, using the expected
and observed exclusions which are quoted for each search channel, we can fully
reconstruct likelihood profiles under very reasonable and simple assumptions.
Even working with this somewhat limited information, we show that our method is
sufficiently accurate to warrant its study and advocate its use over more naive
prescriptions. Using this method, we can begin to narrow in on the remaining
viable parameter space for a Higgs-like scalar state, and to ascertain the
nature of any hints of new physics---Higgs or otherwise---appearing in the
data.Comment: 32 pages, 10 figures; v3: correction made to basis of four-derivative
operators in the effective Lagrangian, references adde

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