25 research outputs found
Anomaly Holography
We consider, in the effective field theory context, anomalies of gauge field
theories on a slice of a five-dimensional, Anti-de Sitter geometry and their
four-dimensional, holographic duals. A consistent effective field theory
description can always be found, notwithstanding the presence of the anomalies
and without modifying the degrees of freedom of the theory. If anomalies do not
vanish, the d=4 theory contains additional pseudoscalar states, which are
either present in the low-energy theory as physical, light states, or are eaten
by (would-be massless) gauge bosons. We show that the pseudoscalars ensure that
global anomalies of the four-dimensional dual satisfy the 't Hooft matching
condition and comment on the relevance for warped models of electroweak
symmetry breaking.Comment: 26 pages, references adde
Improved Higgs Naturalness with Supersymmetry
We present a supersymmetric model of electroweak symmetry-breaking exhibiting
improved naturalness, wherein the stop mass can be pushed beyond the reach of
the Large Hadron Collider without unnatural fine tuning. This implies that
supersymmetry may still solve the hierarchy problem, even if it eludes
detection at the LHC.Comment: 4 pp., to appear in Proceedings of SUSY06, the 14th International
Conference on Supersymmetry and the Unification of Fundamental Interactions,
UC Irvine, California, 12-17 June 200
Linear flavour violation and anomalies in B physics
We propose renormalizable models of new physics that can explain various
anomalies observed in decays of B-mesons to electron and muon pairs. The new
physics states couple to linear combinations of Standard Model fermions,
yielding a pattern of flavour violation that gives a consistent fit to the
gamut of flavour data. Accidental symmetries prevent contributions to baryon-
and lepton-number-violating processes, as well as enforcing a loop suppression
of new physics contributions to flavour violating processes. Data require that
the new flavour-breaking couplings are largely aligned with the Yukawa
couplings of the SM and so we also explore patterns of flavour symmetry
breaking giving rise to this structure.Comment: v2: 28 pages, 10 figures. Added two appendices to make the SU(2)
structure of the model clearer, and to discuss Z/photon penguin
contributions. Updated a bound on Bs mixing, and added references.
Conclusions unchanged. Version to appear in JHE
Polynomials, Riemann surfaces, and reconstructing missing-energy events
We consider the problem of reconstructing energies, momenta, and masses in
collider events with missing energy, along with the complications introduced by
combinatorial ambiguities and measurement errors. Typically, one reconstructs
more than one value and we show how the wrong values may be correlated with the
right ones. The problem has a natural formulation in terms of the theory of
Riemann surfaces. We discuss examples including top quark decays in the
Standard Model (relevant for top quark mass measurements and tests of spin
correlation), cascade decays in models of new physics containing dark matter
candidates, decays of third-generation leptoquarks in composite models of
electroweak symmetry breaking, and Higgs boson decay into two tau leptons.Comment: 28 pages, 6 figures; version accepted for publication, with
discussion of Higgs to tau tau deca
Gaugino mass in AdS space
We study supersymmetric QED in AdS4 with massless matter. At 1-loop the
ultra-violet regulator of the theory generates a contribution to the gaugino
mass that is naively inconsistent with unbroken supersymmetry. We show that
this effect, known in flat space as anomaly mediated supersymmetry breaking, is
required to cancel an infra-red contribution arising from the boundary
conditions in AdS space, which necessarily break chiral symmetry. We also
discuss an analogous UV/IR cancellation that is independent of supersymmetry.Comment: 20 pages, 1 figur
Veneziano-Yankielowicz Superpotential Terms in N=1 SUSY Gauge Theories
The Veneziano-Yankielowicz glueball superpotential for an arbitrary N=1 SUSY
pure gauge theory with classical gauge group is derived using an approach
following recent work of Dijkgraaf, Vafa and others. These non-perturbative
terms, which had hitherto been included by hand in the above approach, are thus
seen to arise naturally, and the approach is rendered self-contained. By
minimising the glueball superpotential for theories with fundamental matter
added, the expected vacuum structure with gaugino condensation and chiral
symmetry breaking is obtained. Various possible extensions are also discussed.Comment: 9 page
Electroweak Baryogenesis in Non-minimal Composite Higgs Models
We address electroweak baryogenesis in the context of composite Higgs models,
pointing out that modifications to the Higgs and top quark sectors can play an
important role in generating the baryon asymmetry. Our main observation is that
composite Higgs models that include a light, gauge singlet scalar in the
spectrum [as in the model based on the symmetry breaking pattern SO(6)/SO(5)],
provide all necessary ingredients for viable baryogenesis. In particular, the
singlet leads to a strongly first-order electroweak phase transition and
introduces new sources of CP violation in dimension-five operators involving
the top quark. We discuss the amount of baryon asymmetry produced and the
experimental constraints on the model.Comment: 15 pages, 7 figure
Beyond the Minimal Composite Higgs Model
The Higgs spectrum of the minimal composite Higgs model, based on the
SO(5)/SO(4) coset, consists of a unique Higgs doublet whose phenomenology does
not differ greatly from the Standard Model (SM). Nevertheless, extensions
beyond this minimal coset structure exhibit a richer Higgs spectrum and
therefore very different Higgs physics. We explore one of these extensions, the
SO(6)/SO(5) model, whose Higgs spectrum contains a CP-odd singlet scalar, eta,
in addition to the Higgs doublet. Due to the pseudo-Nambu-Goldstone nature of
these Higgs bosons, their physical properties can be derived from symmetry
considerations alone. We find that the mass of eta can be naturally light,
opening up the possibility that the SM Higgs decays predominantly to the
singlet, and therefore lowering the LEP bound on its mass to 86 GeV. We also
show that eta can have interesting consequences in flavour-violating processes,
as well as induce spontaneous CP-violation in the Higgs sector. The model can
also have anomalies, giving rise to interactions between the SM gauge bosons
and eta which, if measured at the LHC, would give quantitative information
about the structure of the high energy theory.Comment: 13p
Partially Supersymmetric Composite Higgs Models
We study the idea of the Higgs as a pseudo-Goldstone boson within the
framework of partial supersymmetry in Randall-Sundrum scenarios and their CFT
duals. The Higgs and third generation of the MSSM are composites arising from a
strongly coupled supersymmetric CFT with global symmetry SO(5) spontaneously
broken to SO(4), whilst the light generations and gauge fields are elementary
degrees of freedom whose couplings to the strong sector explicitly break the
global symmetry as well as supersymmetry. The presence of supersymmetry in the
strong sector may allow the compositeness scale to be raised to ~10 TeV without
fine tuning, consistent with the bounds from precision electro-weak
measurements and flavour physics. The supersymmetric flavour problem is also
solved. At low energies, this scenario reduces to the "More Minimal
Supersymmetric Standard Model" where only stops, Higgsinos and gauginos are
light and within reach of the LHC.Comment: 28 pages. v2 minor changes and Refs. adde
Flavourful Production at Hadron Colliders
We ask what new states may lie at or below the TeV scale, with sizable
flavour-dependent couplings to light quarks, putting them within reach of
hadron colliders via resonant production, or in association with Standard Model
states. In particular, we focus on the compatibility of such states with
stringent flavour-changing neutral current and electric-dipole moment
constraints. We argue that the broadest and most theoretically plausible
flavour structure of the new couplings is that they are hierarchical, as are
Standard Model Yukawa couplings, although the hierarchical pattern may well be
different. We point out that, without the need for any more elaborate or
restrictive structure, new scalars with "diquark" couplings to standard quarks
are particularly immune to existing constraints, and that such scalars may
arise within a variety of theoretical paradigms. In particular, there can be
substantial couplings to a pair of light quarks or to one light and one heavy
quark. For example, the latter possibility may provide a flavour-safe
interpretation of the asymmetry in top quark production observed at the
Tevatron. We thereby motivate searches for diquark scalars at the Tevatron and
LHC, and argue that their discovery represents one of our best chances for new
insight into the Flavour Puzzle of the Standard Model.Comment: 18 pp., 8 figures, references adde