3,421 research outputs found

### Mooses, Topology and Higgs

New theories of electroweak symmetry breaking have recently been constructed
that stabilize the weak scale and do not rely upon supersymmetry. In these
theories the Higgs boson is a weakly coupled pseudo-Goldstone boson. In this
note we study the class of theories that can be described by theory spaces and
show that the fundamental group of theory space describes all the relevant
classical physics in the low energy theory. The relationship between the low
energy physics and the topological properties of theory space allow a
systematic method for constructing theory spaces that give any desired low
energy particle content and potential. This provides us with tools for
analyzing and constructing new theories of electroweak symmetry breaking.Comment: 16 pages, 11 figure

### Higher dimensional supersymmetry in 4D superspace

We present an explicit formulation of supersymmetric Yang-Mills theories from
\D= 5 to 10 dimensions in the familiar \N=1,\D=4 superspace. This provides
the rules for globally supersymmetric model building with extra dimensions and
in particular allows us to simply write down $\N=1$ SUSY preserving
interactions between bulk fields and fields localized on branes. We present a
few applications of the formalism by way of illustration, including
supersymmetric ``shining'' of bulk fields, orbifolds and localization of chiral
fermions, anomaly inflow and super-Chern-Simons theories.Comment: Typos corrected. Added reference to early work by Marcus, Sagnotti
and Siegel and a term to the non-Abelian Lagrangian for D>5 formally needed
for gauge invariance. The results however remain unchange

### Infinitely Large New Dimensions

We construct intersecting brane configurations in Anti-de-Sitter space
localizing gravity to the intersection region, with any number $n$ of extra
dimensions. This allows us to construct two kinds of theories with infinitely
large new dimensions, TeV scale quantum gravity and sub-millimeter deviations
from Newton's Law. The effective 4D Planck scale $M_{Pl}$ is determined in
terms of the fundamental Planck scale $M_*$ and the $AdS$ radius of curvature
$L$ via the familiar relation $M_{Pl}^2 \sim M_{*}^{2+n} L^n$; $L$ acts as an
effective radius of compactification for gravity on the intersection. Taking
$M_* \sim$ TeV and $L \sim$ sub-mm reproduces the phenomenology of theories
with large extra dimensions. Alternately, taking $M_* \sim L^{-1} \sim M_{Pl}$,
and placing our 3-brane a distance $\sim 100 M_{Pl}^{-1}$ away from the
intersection gives us a theory with an exponential determination of the
Weak/Planck hierarchy.Comment: 4 pages, revtex, no figure

### Phenomenology of Electroweak Symmetry Breaking from Theory Space

Recently, a new class of realistic models for electroweak symmetry breaking
have been constructed, without supersymmetry. These theories have naturally
light Higgs bosons and perturbative new physics at the TeV scale. We describe
these models in detail, and show that electroweak symmetry breaking can be
triggered by a large top quark Yukawa coupling. A rich spectrum of particles is
predicted, with a pair of light Higgs doublets accompanied by new light weak
triplet and singlet scalars. The lightest of these new scalars is charged under
a geometric discrete symmetry and is therefore stable, providing a new
candidate for WIMP dark matter. At TeV energies, a plethora of new heavy
scalars, gauge bosons and fermions are revealed, with distinctive quantum
numbers and decay modes.Comment: 22 pages, latex, 6 figures. Numerical results corrected,
clarifications added, conclusions unchange

### The Momentum Amplituhedron

In this paper we define a new object, the momentum amplituhedron, which is the long sought-after positive geometry for tree-level scattering amplitudes in N = 4 super Yang-Mills theory in spinor helicity space. Inspired by the construction of the ordinary amplituhedron, we introduce bosonized spinor helicity variables to represent our external kinematical data, and restrict them to a particular positive region. The momentum amplituhedron M n,k is then the image of the positive Grassmannian via a map determined by such kinematics. The scattering amplitudes are extracted from the canonical form with logarithmic singularities on the boundaries of this geometry.Peer reviewedFinal Published versio

### Decoupling Solution to SUSY Flavor Problem via Extra Dimensions

We discuss the decoupling solution to SUSY flavor problem in the fat brane
scenario. We present a simple model to yield the decoupling sfermion spectrum
in a five dimensional theory. Sfermion masses are generated by the overlap
between the wave functions of the matter fields and the chiral superfields on
the SUSY breaking brane. Two explicit examples of the spectrum are given.Comment: 8 pages, LaTe

### Causality, Analyticity and an IR Obstruction to UV Completion

We argue that certain apparently consistent low-energy effective field
theories described by local, Lorentz-invariant Lagrangians, secretly exhibit
macroscopic non-locality and cannot be embedded in any UV theory whose S-matrix
satisfies canonical analyticity constraints. The obstruction involves the signs
of a set of leading irrelevant operators, which must be strictly positive to
ensure UV analyticity. An IR manifestation of this restriction is that the
"wrong" signs lead to superluminal fluctuations around non-trivial backgrounds,
making it impossible to define local, causal evolution, and implying a
surprising IR breakdown of the effective theory. Such effective theories can
not arise in quantum field theories or weakly coupled string theories, whose
S-matrices satisfy the usual analyticity properties. This conclusion applies to
the DGP brane-world model modifying gravity in the IR, giving a simple
explanation for the difficulty of embedding this model into controlled stringy
backgrounds, and to models of electroweak symmetry breaking that predict
negative anomalous quartic couplings for the W and Z. Conversely, any
experimental support for the DGP model, or measured negative signs for
anomalous quartic gauge boson couplings at future accelerators, would
constitute direct evidence for the existence of superluminality and macroscopic
non-locality unlike anything previously seen in physics, and almost
incidentally falsify both local quantum field theory and perturbative string
theory.Comment: 34 pages, 10 figures; v2: analyticity arguments improved, discussion
on non-commutative theories and minor clarifications adde

### Experimental results on searches beyond the Standard Model

Recent results for direct searches for physics beyond the Standard Model are
reviewed. The results include Tevatron II data up to 1.2 fb-1 and HERA results
up to 350 pb-1. Searches for Supersymmetry, for compositeness and for large
extra dimensions are presented. The excess of events with an isolated lepton
and high missing transverse momentum at HERA is discussed.Comment: 10 pages, 15 figures, Plenary talk at the ICHEP06 conference, Moscow,
July 26-August 2, 200

### Experimental hints of Gravity in Large Extra Dimensions?

Recent conjectures suggest the universe may have large extra dimensions,
through which gravity propagates. This implies gross departures from Newton's
law of gravity at small length scales. Here I consider some implications for
particle dynamics on scales comparable to the compactification radius, R_c
\ltorder 1 mm. During planet formation, coalescence of micron sized dust
grains to planetesimals is a rate critical step. Blum et al (2000) found dust
grain aggregates form low fractal dimension structures in microgravity,
consistent with high angular momentum coalescence. I consider the effects of
non-Newtonian gravity on dust aggregation on scales less than $R_c$ and show
they naturally coalesce into low dimensional structures with high specific
angular momentum. We infer $R_c \approx 80$ microns.Comment: 5 pages, revtex, Int. Jour. Mod. Phys. D (Special issue of GRF essays
2001), single spaced versio

### Testing gravity in Large Extra Dimensions using Bose-Einstein Condensates

Recent conjectures that there are mesoscopically ``large'' extra dimensions,
through which gravity propagates have interesting implications for much of
physics. The scenario implies gross departures from Newton's law of gravity at
small length scales. Testing departures from Coulomb's law on sub-millimetre
scales is hard. It is now possible to routinely create Bose-Einstein
condensates with de Broglie wavelengths of order a $\mu m$ and total size of
order $10 \mu m$. BEC condensates move coherently under gravitational
acceleration, and I propose that the transverse fringe shift due to the
acceleration of pair of interfering BECs passing a dense linear mass may be
measurable, and provide direct evidence for anomalous gravitational
acceleration. Ideally such experiments are best carried out in free fall to
maximise the time spent by a BEC in the non-Newtonian regime.Comment: 2 pages, double column, revtex, no figures Int J. Mod Phys D.
(Special issue of GRF essays 2002). Int. J. Mod. Phys. D. in pres

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