238 research outputs found
Naturally Light Scalars
I argue that in certain chiral gauge theories composite scalars associated
with chiral symmetry breaking can be light (i.e. lighter than naive scaling
from QCD would suggest) without any fine-tuning. These scalars will be even
lighter in chiral gauge theories that produce chiral symmetry breaking without
confinement. I construct a model which demonstrates this last possibility.Comment: 12 pages, LaTe
Glueballs and AdS/CFT
I review the calculation of the glueball spectrum in non-supersymmetric
Yang-Mills theory (in 3 and 4 dimensions) using the conjectured duality between
supergravity and large N gauge theories. The glueball masses are obtained by
solving the supergravity wave equations in a black hole geometry. The masses
obtained this way are in unexpectedly good agreement with the available lattice
data, and are much better than strong-coupling expansion results. I also show
how to use a modified version of the duality to calculate the glueball mass
spectrum with some of the Kaluza-Klein states of the supergravity theory
decoupled from the spectrum.Comment: 10 pages, 1 figure. Invited talk, "The Phenomenology of Large-Nc
QCD", to be published in Proceedings of the Institute of Nuclear Theor
Glueball Mass Spectrum from Supergravity
We review the calculation of the spectrum of glueball masses in
non-supersymmetric Yang-Mills theory using the conjectured duality between
supergravity and large N gauge theories. The glueball masses are obtained by
solving the supergravity wave equations in a black hole geometry. The glueball
masses found this way are in unexpected agreement with the available lattice
data. We also show how to use a modified version of the duality based on
rotating branes to calculate the glueball mass spectrum with some of the
Kaluza-Klein states of the supergravity theory decoupled from the spectrum.Comment: 7 pages, RevTeX. Based on two talks presented at DPF '99, UCLA, Los
Angeles, CA, 5-9 January, 199
Negative contributions to S in an effective field theory
We show that an effective field theory that includes non-standard couplings
between the electroweak gauge bosons and the top and bottom quarks may yield
negative contributions to both the S and T oblique radiative electroweak
parameters. We find that that such an effective field theory provides a better
fit to data than the standard model (the chi-squared per degree of freedom is
half as large). We examine in some detail an illustrative model where the
exchange of heavy scalars produces the correct type of non-standard couplings.Comment: 12 pages, 1 fig., LaTeX, typos corrected, improved referencin
Marginal Breaking of Conformal SUSY QCD
We provide an example of a 4D theory that exhibits the
Contino-Pomarol-Rattazzi mechanism, where breaking conformal symmetry by an
almost marginal operator leads to a light pseudo-Goldstone boson, the dilaton,
and a parametrically suppressed contribution to vacuum energy. We consider SUSY
QCD at the edge of the conformal window and break conformal symmetry by weakly
gauging a subgroup of the flavor symmetry. Using Seiberg duality we show that
for a range of parameters the singlet meson in the dual theory reaches the
unitarity bound, however, this theory does not have a stable vacuum. We
stabilize the vacuum with soft breaking terms, compute the mass of the dilaton,
and determine the range of parameters where the leading contribution to the
dilaton mass is from the almost marginal coupling.Comment: 12 pages, no figure
Little Conformal Symmetry
We explore a new class of natural models which ensure the one-loop
divergences in the Higgs mass are cancelled. The top-partners that cancel the
top loop are new gauge bosons, and the symmetry relation that ensures the
cancellation arises at an infrared fixed point. Such a cancellation mechanism
can, a la Little Higgs models, push the scale of new physics that completely
solves the hierarchy problem up to 5-10 TeV. When embedded in a supersymmetric
model, the stop and gaugino masses provide the cutoffs for the loops, and the
mechanism ensures a cancellation between the stop and gaugino mass dependence
of the Higgs mass parameter.Comment: 15 pages, 3 figure
A Light Stop with a Heavy Gluino: Enlarging the Stop Gap
It is widely thought that increasing bounds on the gluino mass, which feeds
down to the stop mass through renormalization group running, are making a light
stop increasingly unlikely. Here we present a counter-example. We examine the
case of the Minimal Composite Supersymmetric Standard Model which has a light
composite stop. The large anomalous dimension of the stop from strong dynamics
pushes the stop mass toward a quasi-fixed point in the infrared, which is
smaller than standard estimates by a factor of a large logarithm. The gluino
can be about three times heavier than the stop, which is comparable to
hierarchy achieved with supersoft Dirac gluino masses. Thus, in this class of
models, a heavy gluino is not necessarily indicative of a heavy stop.Comment: 6 pages, 1 figur
Light Stops from Seiberg Duality
If low-energy supersymmetry is realized in nature, a seemingly contrived
hierarchy in the squark mass spectrum appears to be required. We show that
composite supersymmetric theories at the bottom of the conformal window can
automatically yield the spectrum that is suggested by experimental data and
naturalness. With a non-tuned choice of parameters, the only superpartners
below one TeV will be the partners of the Higgs, the electroweak gauge bosons,
the left-handed top and bottom, and the right-handed top, which are precisely
the particles needed to make weak scale supersymmetry breaking natural. In the
model considered here, these correspond to composite (or partially composite)
degrees of freedom via Seiberg duality, while the other MSSM fields, with their
heavier superpartners, are elementary. The key observation is that at or near
the edge of the conformal window, soft supersymmetry breaking scalar and
gaugino masses are transmitted only to fundamental particles at leading order.
With the potential that arises from the duality, a Higgs with a 125 GeV mass,
with nearly SM production rates, is naturally accommodated without tuning. The
lightest ordinary superpartner is either the lightest stop or the lightest
neutralino. If it is the stop, it is natural for it to be almost degenerate
with the top, in which case it decays to top by emitting a very soft gravitino,
making it quite difficult to find this mode at the LHC and more challenging to
find SUSY in general, yielding a simple realization of the stealth
supersymmetry idea. We analyze four benchmark spectra in detail.Comment: 27 pages, 2 figure
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