1,215 research outputs found
Baryon masses at second order in large- chiral perturbation theory
We consider flavor breaking in the the octet and decuplet baryon masses at
second order in large- chiral perturbation theory, where is the number
of QCD colors. We assume that , where is the number of light quark
flavors, and are the parameters controlling
flavor breaking in chiral perturbation theory. We consistently include
non-analytic contributions to the baryon masses at orders , , and . The corrections are small for
the relations that follow from symmetry alone, but the corrections to
the large- relations are large and have the wrong sign. Chiral
power-counting and large- consistency allow a 2-loop contribution at order
, and a non-trivial explicit calculation is required to show
that this contribution vanishes. At second order in the expansion, there are
eight relations that are non-trivial consequences of the expansion, all
of which are well satisfied within the experimental errors. The average
deviation at this order is 7 \MeV for the \De I = 0 mass differences and
0.35 \MeV for the \De I \ne 0 mass differences, consistent with the
expectation that the error is of order .Comment: 19 pages, 2 uuencoded ps figs, uses revte
Mediation of supersymmetry breaking in extra dimensions
We review the mechanisms of supersymmetry breaking mediation that occur in
sequestered models, where the visible and the hidden sectors are separated by
an extra dimension and communicate only via gravitational interactions. By
locality, soft breaking terms are forbidden at the classical level and reliably
computable within an effective field theory approach at the quantum level. We
present a self-contained discussion of these radiative gravitational effects
and the resulting pattern of soft masses, and give an overview of realistic
model building based on this set-up. We consider both flat and warped extra
dimensions, as well as the possibility that there be localized kinetic terms
for the gravitational fields.Comment: LaTex, 15 pages; brief review prepared for MPLA. v2: minor
correction
Spherical Collapse and the Halo Model in Braneworld Gravity
We present a detailed study of the collapse of a spherical perturbation in
DGP braneworld gravity for the purpose of modeling simulation results for the
halo mass function, bias and matter power spectrum. The presence of evolving
modifications to the gravitational force in form of the scalar brane-bending
mode lead to qualitative differences to the collapse in ordinary gravity. In
particular, differences in the energetics of the collapse necessitate a new,
generalized method for defining the virial radius which does not rely on strict
energy conservation. These differences and techniques apply to smooth dark
energy models with w unequal -1 as well. We also discuss the impact of the
exterior of the perturbation on collapse quantities due to the lack of a
Birkhoff theorem in DGP. The resulting predictions for the mass function, halo
bias and power spectrum are in good overall agreement with DGP N-body
simulations on both the self-accelerating and normal branch. In particular, the
impact of the Vainshtein mechanism as measured in the full simulations is
matched well. The model and techniques introduced here can serve as practical
tools for placing consistent constraints on braneworld models using
observations of large scale structure.Comment: 20 pages, 16 figures; v2: minor addition to appendix; matches
published version; v3: typos in Eqs. (20), (23) correcte
Supergravity loop contributions to brane world supersymmetry breaking
We compute the supergravity loop contributions to the visible sector scalar
masses in the simplest 5D `brane-world' model. Supersymmetry is assumed to be
broken away from the visible brane and the contributions are UV finite due to
5D locality. We perform the calculation with N = 1 supergraphs, using a
formulation of 5D supergravity in terms of N = 1 superfields. We compute
contributions to the 4D effective action that determine the visible scalar
masses, and we find that the mass-squared terms are negative.Comment: 12 pages, LaTeX 2
Visible Effects of the Hidden Sector
The renormalization of operators responsible for soft supersymmetry breaking
is usually calculated by starting at some high scale and including only visible
sector interactions in the evolution equations, while ignoring hidden sector
interactions. Here we explain why this is correct only for the most trivial
structures in the hidden sector, and discuss possible implications. This
investigation was prompted by the idea of conformal sequestering. In that
framework hidden sector renormalizations by nearly conformal dynamics are
critical. In the original models of conformal sequestering it was necessary to
impose hidden sector flavor symmetries to achieve the sequestered form. We
present models which can evade this requirement and lead to no-scale or anomaly
mediated boundary conditions; but the necessary structures do not seem generic.
More generally, the ratios of scalar masses to gaugino masses, the -term,
the -term, -terms, and the gravitino mass can be significantly
affected.Comment: 23 pages, no figure
The Unhiggs
We examine a scenario where the Higgs is part of an approximate conformal
field theory, and has a scaling dimension greater than one. Such an unparticle
Higgs (or Unhiggs) can still break electroweak symmetry and unitarize WW
scattering, but its gauge couplings are suppressed. An Unhiggs model has a
reduced sensitivity of the weak scale to the cutoff, and can thus provide a
solution to the little hierarchy problem.Comment: 21 pages, 9 figures; v2: further discussion, references added,
version published in JHE
Effective Action and Holography in 5D Gauge Theories
We apply the holographic method to 5D gauge theories on the warped interval.
Our treatment includes the scalars associated with the fifth gauge field
component, which appear as 4D Goldstone bosons in the holographic effective
action. Applications are considered to two classes of models in which these
scalars play an important role. In the Composite-Higgs (and/or Gauge-Higgs
Unification) scenario, the scalars are interpreted as the Higgs field and we
use the holographic recipe to compute its one-loop potential. In AdS/QCD
models, the scalars are identified with the mesons and we compute
holographically the Chiral Perturbation Theory Lagrangian up to p^4 order. We
also discuss, using the holographic perspective, the effect of including a
Chern-Simons term in the 5D gauge Lagrangian. We show that it makes a
Wess-Zumino-Witten term to appear in the holographic effective action. This is
immediately applied to AdS/QCD, where a Chern-Simons term is needed in order to
mimic the Adler-Bardeen chiral anomaly.Comment: 37 pages; v2, minor changes, one reference added; v3, minor
corrections, version published in JHE
Supersymmetry and Electroweak Breaking in the Interval
Hypermultiplets are considered in the five-dimensional interval where all
fields are continuous and the boundary conditions are dynamically obtained from
the action principle. The orbifold boundary conditions are obtained as
particular cases. We can interpret the Scherk-Schwarz supersymmetry breaking as
a misalignment of boundary conditions while a new source of supersymmetry
breaking corresponding to a mismatch of different boundary parameters is
identified. The latter can be viewed as coming from boundary supersymmetry
breaking masses for hyperscalars and the nature of the corresponding
supersymmetry breaking parameter is analyzed. For some regions of the parameter
space where supersymmetry is broken (either by Scherk-Schwarz boundary
conditions or by boundary hyperscalar masses) electroweak symmetry breaking can
be triggered at the tree level.Comment: 28 pages, 5 figure
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