834 research outputs found
Central Charge Bounds in 4D Conformal Field Theory
We derive model-independent lower bounds on the stress tensor central charge
C_T in terms of the operator content of a 4-dimensional Conformal Field Theory.
More precisely, C_T is bounded from below by a universal function of the
dimensions of the lowest and second-lowest scalars present in the CFT. The
method uses the crossing symmetry constraint of the 4-point function, analyzed
by means of the conformal block decomposition.Comment: 16 pages, 6 figure
Supersymmetry-Breaking Loops from Analytic Continuation into Superspace
We extend to all orders in perturbation theory a method to calculate
supersymmetry-breaking effects by analytic continuation of the renormalization
group into superspace. A central observation is that the renormalized gauge
coupling can be extended to a real vector superfield, thereby including soft
breaking effects in the gauge sector. We explain the relation between this
vector superfield coupling and the "holomorphic" gauge coupling, which is a
chiral superfield running only at 1 loop. We consider these issues for a number
of regulators, including dimensional reduction. With this method, the
renormalization group equations for soft supersymmetry breaking terms are
directly related to supersymmetric beta functions and anomalous dimensions to
all orders in perturbation theory. However, the real power of the formalism
lies in computing finite soft breaking effects corresponding to high-loop
component calculations. We prove that the gaugino mass in gauge-mediated
supersymmetry breaking is ``screened'' from strong interactions in the
messenger sector. We present the complete next-to-leading calculation of
gaugino masses (2 loops) and sfermion masses (3 loops) in minimal gauge
mediation, and several other calculations of phenomenological relevance.Comment: 50 pages, 1 ps and 1 eps figure, LaTe
Classical and Quantum Consistency of the DGP Model
We study the Dvali-Gabadadze-Porrati model by the method of the boundary
effective action. The truncation of this action to the bending mode \pi
consistently describes physics in a wide range of regimes both at the classical
and at the quantum level. The Vainshtein effect, which restores agreement with
precise tests of general relativity, follows straightforwardly. We give a
simple and general proof of stability, i.e. absence of ghosts in the
fluctuations, valid for most of the relevant cases, like for instance the
spherical source in asymptotically flat space. However we confirm that around
certain interesting self-accelerating cosmological solutions there is a ghost.
We consider the issue of quantum corrections. Around flat space \pi becomes
strongly coupled below a macroscopic length of 1000 km, thus impairing the
predictivity of the model. Indeed the tower of higher dimensional operators
which is expected by a generic UV completion of the model limits predictivity
at even larger length scales. We outline a non-generic but consistent choice of
counterterms for which this disaster does not happen and for which the model
remains calculable and successful in all the astrophysical situations of
interest. By this choice, the extrinsic curvature K_{\mu\nu} acts roughly like
a dilaton field controlling the strength of the interaction and the cut-off
scale at each space-time point. At the surface of Earth the cutoff is \sim 1 cm
but it is unlikely that the associated quantum effects be observable in table
top experiments.Comment: 26 pages, 1 eps figur
OPE Convergence in Conformal Field Theory
We clarify questions related to the convergence of the OPE and conformal
block decomposition in unitary Conformal Field Theories (for any number of
spacetime dimensions). In particular, we explain why these expansions are
convergent in a finite region. We also show that the convergence is
exponentially fast, in the sense that the operators of dimension above Delta
contribute to correlation functions at most exp(-a Delta). Here the constant
a>0 depends on the positions of operator insertions and we compute it
explicitly.Comment: 26 pages, 6 figures; v2: a clarifying note and two refs added; v3:
note added concerning an extra constant factor in the main error estimate,
misprint correcte
Top and Bottom: a Brane of Their Own
We consider extra dimensional descriptions of models where there are two
separate strongly interacting sectors contributing to electroweak symmetry
breaking (``topcolor'' type models). In the extra dimensional picture there
would be two separate (anti-de Sitter) bulks meeting on the Planck brane, with
each bulk having its own corresponding IR (TeV) brane. Sources for electroweak
symmetry breaking can then be localized on both of these IR branes, while the
different generations of fermions may be separated from each other. We describe
the modes propagating in such a setup, and consider the cases where the
electroweak symmetry breaking on either of the two IR branes come either from a
higgsless scenario (via boundary conditions) or a (top-)Higgs. We show that the
tension that exists between obtaining a large top quark mass and the correct
value of the Zb\bar{b} couplings in ordinary higgsless models can be largely
relieved in the higgsless--top-Higgs versions of the two IR brane models. This
may also be true in the purely higgsless--higgsless case, however since that
model is necessarily in the strongly coupled regime the tree-level results for
the properties of the third generation may get large corrections. A necessary
consequence of such models is the appearance of additional pseudo-Goldstone
bosons (``top-pions''), which would be strongly coupled to the third
generation.Comment: 34 pages, LaTeX, 6 figures. v2: figure 2 fixed, footnote, comments
and references adde
Partly Supersymmetric Grand Unification
It is shown how grand unification can occur in models which are partly
supersymmetric. The particle states which are composite do not contribute to
the running of gauge couplings above the compositeness scale, while the
elementary states contribute the usual large logarithmns. This introduces a new
differential running contribution to the gauge couplings from partly composite
SU(5) matter multiplets. In particular, for partly supersymmetric models, the
incomplete SU(5) elementary matter multiplets restore gauge coupling
unification even though the usual elementary gaugino and Higgsino contributions
need not be present.Comment: 14 pages, LaTe
High Energy Field Theory in Truncated AdS Backgrounds
In this letter we show that, in five-dimensional anti-deSitter space (AdS)
truncated by boundary branes, effective field theory techniques are reliable at
high energy (much higher than the scale suggested by the Kaluza-Klein mass
gap), provided one computes suitable observables. We argue that in the model of
Randall and Sundrum for generating the weak scale from the AdS warp factor, the
high energy behavior of gauge fields can be calculated in a {\em cutoff
independent manner}, provided one restricts Green's functions to external
points on the Planck brane. Using the AdS/CFT correspondence, we calculate the
one-loop correction to the Planck brane gauge propagator due to charged bulk
fields. These effects give rise to non-universal logarithmic energy dependence
for a range of scales above the Kaluza-Klein gap.Comment: LaTeX, 7 pages; minor typos fixe
Holography for fermions
The holographic interpretation is a useful tool to describe 5D field theories
in a 4D language. In particular it allows one to relate 5D AdS theories with 4D
CFTs. We elaborate on the 5D/4D dictionary for the case of fermions in AdS
with boundaries. This dictionary is quite useful to address phenomenological
issues in a very simple manner, as we show by giving some examples.Comment: 22 pages, 2 figures; v2: minor corrections, references adde
The Three Dimensional Dual of 4D Chirality
Chiral gauge theories can be defined in four-dimensional Anti de Sitter
space, but AdS boundary conditions explicitly break the chiral symmetry in a
specific, well defined manner, which in turns results in an anomalous Ward
identity. When the 4D theory admits a dual description in terms of a 3D CFT,
the 3D dual of the broken chiral symmetry is a certain double-trace deformation
of the CFT, which produces the same anomalous chiral Ward identities that
obtains in the 4D bulk theory.Comment: 10 pages, small misprints corrected, reference [16] updated. Version
to appear in JHE
More Holography from Conformal Field Theory
We extend the work of [4] to support the conjecture that any conformal field
theory with a large N expansion and a large gap in the spectrum of anomalous
dimensions has a local bulk dual. We count to O(1/N^2) the solutions to the
crossing constraints in conformal field theory for a completely general scalar
four-point function and show that, to this order, the counting matches the
number of independent interactions in a general scalar theory on Anti-de Sitter
space. We introduce parity odd conformal blocks for this purpose.Comment: 19 page
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