574 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
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
Anomaly Mediated Supersymmetry Breaking in Four Dimensions, Naturally
We present a simple four-dimensional model in which anomaly mediated
supersymmetry breaking naturally dominates. The central ingredient is that the
hidden sector is near a strongly-coupled infrared fixed-point for several
decades of energy below the Planck scale. Strong renormalization effects then
sequester the hidden sector from the visible sector. Supersymmetry is broken
dynamically and requires no small input parameters. The model provides a
natural and economical explanation of the hierarchy between the
supersymmetry-breaking scale and the Planck scale, while allowing anomaly
mediation to address the phenomenological challenges posed by weak scale
supersymmetry. In particular, flavor-changing neutral currents are naturally
near their experimental limits.Comment: 14 pages, Late
Renormalizations in softly broken N=1 theories: Slavnov-Taylor identities
Slavnov-Taylor identities have been applied to perform explicitly the
renormalization procedure for the softly broken N=1 SYM. The result is in
accordance with the previous results obtained at the level of supergraph
technique.Comment: Latex, 17 pages, one statement about soft gauge beta function has
been change
"Gaugomaly" Mediated SUSY Breaking and Conformal Sequestering
Anomaly-mediated supersymmetry breaking in the context of 4D conformally
sequestered models is combined with Poppitz-Trivedi D-type gauge-mediation. The
implementation of the two mediation mechanisms naturally leads to visible soft
masses at the same scale so that they can cooperatively solve the mu and flavor
problems of weak scale supersymmetry, as well as the tachyonic slepton problem
of pure anomaly-mediation. The tools are developed in a modular fashion for
more readily fitting into the general program of optimizing supersymmetric
dynamics in hunting for the most attractive weak scale phenomenologies combined
with Planck-scale plausibility.Comment: 14 pages, Late
Baryons with Many Colors and Flavors
Using recently-developed diagrammatic techniques, I derive some general
results concerning baryons in the expansion, where is the number of
QCD colors. I show that the spin-flavor relations which hold for baryons in the
large- limit, as well as the form of the corrections to these relations at
higher orders in , hold even if , where is the
number of light quark flavors. I also show that the amplitude for a baryon to
emit mesons is , and that meson loops attached to
baryon lines are unsupressed in the large- limit, independent of . For
, there are ambiguities in the extrapolation away from because
the baryon flavor multiplets for a given spin grow with . I argue that the
expansion is valid for baryons with spin and {\it arbitrary}
flavor quantum numbers, including e.g. baryons with isospin and/or strangeness
. This allows the formulation of a large- expansion in which it is not
necessary to identify the physical baryons with particular large- states.
symmetry can be made manifest to all orders in , yet group
theory factors must be evaluated explicitly only for . To
illustrate this expansion, I consider the non-singlet axial currents, baryon
mass splittings, and matrix elements of \mybar ss and \mybar s \gam_\mu
\gam_5 s in the nucleon.Comment: 19 pages, plain TeX, 4 uuencoded postscrip figures, LBL-35539,
NSF-ITP-94-4
Composite Quarks and Leptons from Dynamical Supersymmetry Breaking without Messengers
We present new theories of dynamical SUSY breaking in which the strong
interactions that break SUSY also give rise to composite quarks and leptons
with naturally small Yukawa couplings. In these models, SUSY breaking is
communicated directly to the composite fields without ``messenger''
interactions. The compositeness scale can be anywhere between 10 TeV and the
Planck scale. These models can naturally solve the supersymmetric flavor
problem, and generically predict sfermion mass unification independent from
gauge unification.Comment: 27 pages, LaTeX; Clarified flavor symmetry of strong interactions;
corrected overestimate of FCNC's; conclusions strengthene
Consistency of the Baryon-Multimeson Amplitudes for Large-N_c QCD
We study the pion-baryon scattering process in a QCD
theory with a large number (N_c) of colors. It is known that this scattering
amplitudes decreases with N_c like N_c^{1-n/2}, and that its individual tree
diagrams grow like N_c^{n/2}. The only way these two can be consistent is for
n-1 powers of N_c to be cancelled when the Feynman diagrams are summed. We
prove this to be true in tree order for any n.Comment: latex file with two postscript figure
Radius Stabilization and Anomaly-Mediated Supersymmetry Breaking
We analyze in detail a specific 5-dimensional realization of a
"brane-universe" scenario where the visible and hidden sectors are localized on
spatially separated 3-branes coupled only by supergravity, with supersymmetry
breaking originating in the hidden sector. Although general power counting
allows order 1/M_{Planck}^2 contact terms between the two sectors in the
4-dimensional theory from exchange of supergravity Kaluza-Klein modes, we show
that they are not present by carefully matching to the 5-dimensional theory. We
also find that the radius modulus corresponding to the size of the compactified
dimension must be stabilized by additional dynamics in order to avoid run-away
behavior after supersymmetry breaking and to understand the communication of
supersymmetry breaking. We stabilize the radius by adding two pure Yang--Mills
sectors, one in the bulk and the other localized on a brane. Gaugino
condensation in the 4-dimensional effective theory generates a superpotential
that can naturally fix the radius at a sufficiently large value that
supersymmetry breaking is communicated dominantly by the recently-discovered
mechanism of anomaly mediation. The mass of the radius modulus is large
compared to m_{3/2}. The stabilization mechanism requires only parameters of
order one at the fundamental scale, with no fine-tuning except for the
cosmological constant.Comment: 20 pages, LaTeX2
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