1,388 research outputs found
vs. Breaking in Weak Hyperon Decays
We consider the predictions of chiral perturbation theory for
breaking in weak semileptonic and -wave nonleptonic hyperon decays. By
defining an expansion sensitive only to breaking, we show that the
leading corrections give rise to moderate corrections to relations
(\lsim 20\%), even though the {\it chiral} symmetry
appears to be rather badly broken. This explains why fits to weak
hyperon decays work well even though chiral-symmetry breaking corrections are
large. Applying these -breaking corrections to the analysis of the EMC
data, we find that the predicted value of \bra p\mybar s\gamma_\mu\gamma_5
s\ket p is reduced by , suggesting that the ``EMC effect'' may be
less striking than commonly thought.Comment: 15 pages, LBL-33993/CfPA-TH-93-09. (Eliminated multiple fonts in
title; some versions of TeX apparently cannot handle this. No change in
text.
Soft Supersymmetry Breaking in Deformed Moduli Spaces, Conformal Theories, and N = 2 Yang-Mills Theory
We give a self-contained discussion of recent progress in computing the
non-perturbative effects of small non-holomorphic soft supersymmetry breaking,
including a simple new derivation of these results based on an anomaly-free
gauged U(1)_R background. We apply these results to N = 1 theories with
deformed moduli spaces and conformal fixed points. In an SU(2) theory with a
deformed moduli space, we completely determine the vacuum expectation values
and induced soft masses. We then consider the most general soft breaking of
supersymmetry in N = 2 SU(2) super-Yang-Mills theory. An N = 2 superfield
spurion analysis is used to give an elementary derivation of the relation
between the modulus and the prepotential in the effective theory. This analysis
also allows us to determine the non-perturbative effects of all soft terms
except a non-holomorphic scalar mass, away from the monopole points. We then
use an N = 1 spurion analysis to determine the effects of the most general soft
breaking, and also analyze the monopole points. We show that naive dimensional
analysis works perfectly. Also, a soft mass for the scalar in this theory
forces the theory into a free Coulomb phase.Comment: 37 pages, LaTeX2e, 4 eps figure
Radion Mediated Supersymmetry Breaking
We point out that in supersymmetric theories with extra dimensions, radius
stabilization can give rise to a VEV for the component of the radius
modulus. This gives an important contribution to supersymmetry breaking of
fields that propagate in the bulk. A particularly attractive class of models is
obtained if the standard-model gauge fields propagate in the bulk, while the
quark and lepton fields are localized on a brane. This leads to gaugino
mediated supersymmetry breaking without the need for singlets in the hidden
sector. We analyze a simple explicit model in which this idea is realized
Renormalization of Entanglement Entropy and the Gravitational Effective Action
The entanglement entropy associated with a spatial boundary in quantum field
theory is UV divergent, with the leading term proportional to the area of the
boundary. For a class of quantum states defined by a path integral, the
Callan-Wilczek formula gives a geometrical definition of the entanglement
entropy. We show that, for this class of quantum states, the entanglement
entropy is rendered UV-finite by precisely the counterterms required to cancel
the UV divergences in the gravitational effective action. In particular, the
leading contribution to the entanglement entropy is given by the renormalized
Bekenstein-Hawking formula, in accordance with a proposal of Susskind and
Uglum. We show that the subleading UV-divergent terms in the entanglement
entropy depend nontrivially on the quantum state. We compute new subleading
terms in the entanglement entropy and find agreement with the Wald entropy
formula for black hole spacetimes with bifurcate Killing horizons. We speculate
that the entanglement entropy of an arbitrary spatial boundary may be a
well-defined observable in quantum gravity.Comment: 26 pages, 2 figures. v2: minor corrections and clarification
Superconformal Technicolor
In supersymmetric theories with a strong conformal sector, soft supersymmetry
breaking at the TeV scale naturally gives rise to confinement and chiral
symmetry breaking at the same scale. We investigate models where such a sector
dynamically breaks electroweak symmetry. We consider two scenarios, one where
the strong dynamics induces vacuum expectation values for elementary Higgs
fields, and another where the strong dynamics is solely responsible for
electroweak symmetry breaking. In both cases there is no fine tuning required
to explain the absence of a Higgs boson below the LEP bound, solving the
supersymmetry naturalness problem. A good precision electroweak fit can be
obtained, and quark and lepton masses are generated without flavor-changing
neutral currents. Electroweak symmetry breaking may be dominated either by the
elementary Higgs bosons or by the strong dynamics. In addition to standard
superymmetry collider signals, these models predict production of multiple
heavy standard model particles (t, W, Z, and b) from decays of resonances in
the strong sector.Comment: 4 pages; v2: minor changes, references adde
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