189 research outputs found
Hard Scattering and Gauge/String Duality
We consider high-energy fixed-angle scattering of glueballs in confining
gauge theories that have supergravity duals. Although the effective description
is in terms of the scattering of strings, we find that the amplitudes are hard
(power law). This is a consequence of the warped geometry of the dual theory,
which has the effect that in an inertial frame the string process is never in
the soft regime. At small angle we find hard and Regge behaviors in different
kinematic regions.Comment: 4 page
Stealth Supersymmetry
We present a broad class of supersymmetric models that preserve R-parity but
lack missing energy signatures. These models have new light particles with
weak-scale supersymmetric masses that feel SUSY breaking only through couplings
to the MSSM. This small SUSY breaking leads to nearly degenerate fermion/boson
pairs, with small mass splittings and hence small phase space for decays
carrying away invisible energy. The simplest scenario has low-scale SUSY
breaking, with missing energy only from soft gravitinos. This scenario is
natural, lacks artificial tunings to produce a squeezed spectrum, and is
consistent with gauge coupling unification. The resulting collider signals will
be jet-rich events containing false resonances that could resemble signatures
of R-parity violation. We discuss several concrete examples of the general
idea, and emphasize gamma + jet + jet resonances, displaced vertices, and very
large numbers of b-jets as three possible discovery modes.Comment: 12 pages, 4 figure
Composite Supersymmetries in low-dimensional systems
Starting from a N=1 scalar supermultiplet in 2+1 dimensions, we demonstrate
explicitly the appearance of induced N=1 vector and scalar supermultiplets of
composite operators made out of the fundamental supersymmetric constituents. We
discuss an extension to a N=2 superalgebra with central extension, due to the
existence of topological currents in 2+1 dimensions. As a specific model we
consider a supersymmetric -model as the constituent theory, and
discuss the relevance of these results for an effective description of the
infrared dynamics of planar high-temperature superconducting condensed matter
models with quasiparticle excitations near nodal points of their Fermi surface.Comment: 20 pages Latex, no figure
Stringy Instantons and Cascading Quivers
D-brane instantons can perturb the quantum field theories on space-time
filling D-branes by interesting operators. In some cases, these D-brane
instantons are novel "stringy" effects (not interpretable directly as instanton
effects in the low-energy quantum field theory), while in others the D-brane
instantons can be directly interpreted as field theory effects. In this note,
we describe a situation where both perspectives are available, by studying
stringy instantons in quivers which arise at simple Calabi-Yau singularities.
We show that a stringy instanton which wraps an unoccupied node of the quiver,
and gives rise to a non-perturbative mass in the space-time field theory, can
be reinterpreted as a conventional gauge theory effect by going up in an
appropriate renormalization group cascade. Interestingly, in the cascade, the
contribution of the stringy instanton does not come from gauge theory
instantons but from strong coupling dynamics.Comment: 17 pages, 6 figures, harvma
Non-Perturbative Planar Equivalence and the Absence of Closed String Tachyons
We consider 'orbifold' and 'orientifold' field theories from the dual closed
string theory side. We argue that a necessary condition for planar equivalence
to hold is the absence of a closed string tachyonic mode in the dual
non-supersymmetric string. We analyze several gauge theories on R3xS1. In the
specific case of U(N) theories with symmetric/anti-symmetric fermions
('orientifold field theories') the relevant closed string theory is
tachyon-free at large compactification radius (due to winding modes), but it
develops a tachyonic mode below a critical radius. Our finding is with
agreement with field theory expectations of a phase transition from a C-parity
violating phase to a C-parity preserving phase as the compactification radius
increases. In the case of U(N)xU(N) theories with bi-fundamental matter
('orbifold field theories') a tachyon is always present in the string spectrum,
at any compactification radius. We conclude that on R4 planar equivalence holds
for 'orientfiold field theories', but fails for 'orbifold field theories'
daughters of N=4 SYM and suggest the same for daughters of N=1 SYM. We also
discuss examples of SO/Sp gauge theories with symmetric/anti-symmetric
fermions. In this case planar equivalence holds at any compactification radius
-in agreement with the absence of tachyons in the string dual.Comment: 14 pages, Latex. 3 eps figures. v2: ref. added. v3: clarifying
sentences added in the abstract and at the end of section 4. version accepted
to JHE
Supersymmetric Three-Form Flux Perturbations on
We consider warped type IIB supergravity solutions with three-form flux and
supersymmetry, which arise as the supergravity duals of confining
gauge theories. We first work in a perturbation expansion around , as in the work of Polchinski and Strassler, and from the
conditions and the Bianchi identities recover their first-order solution
generalized to an arbitrary superpotential. We find the second
order dilaton and axion by the same means. We also find a simple family of
exact solutions, which can be obtained from solutions found by Becker and
Becker, and which includes the recent Klebanov--Strassler solution.Comment: 19 pages. reference added, minor clarifications. v3: reference to
non-Abelian BPS monopole solution corrected (Chamseddine-Volkov
From Free Fields to AdS -- II
We continue with the program of hep-th/0308184 to implement open-closed
string duality on free gauge field theory (in the large limit). In this
paper we consider correlators such as \la \prod_{i=1}^n
\Tr\Phi^{J_i}(x_i)\ra. The Schwinger parametrisation of this -point
function exhibits a partial gluing up into a set of basic skeleton graphs. We
argue that the moduli space of the planar skeleton graphs is exactly the same
as the moduli space of genus zero Riemann surfaces with holes. In other
words, we can explicitly rewrite the -point (planar) free field correlator
as an integral over the moduli space of a sphere with holes. A preliminary
study of the integrand also indicates compatibility with a string theory on
. The details of our argument are quite insensitive to the specific form
of the operators and generalise to diagrams of higher genus as well. We take
this as evidence of the field theory's ability to reorganise itself into a
string theory.Comment: 26 pages, 2 figures; v2. some additional comments, references adde
Deconfinement transition and string tensions in SU(4) Yang-Mills Theory
We present results from numerical lattice calculations of SU(4) Yang-Mills
theory. This work has two goals: to determine the order of the finite
temperature deconfinement transition on an lattice and to study the
string tensions between static charges in the irreducible representations of
SU(4). Motivated by Pisarski and Tytgat's argument that a second-order
SU() deconfinement transition would explain some features of the SU(3)
and QCD transitions, we confirm older results on a coarser, , lattice.
We see a clear two-phase coexistence signal, characteristic of a first-order
transition, at on a lattice, on which we also
compute a latent heat of . Computing
Polyakov loop correlation functions we calculate the string tension at finite
temperature in the confined phase between fundamental charges, ,
between diquark charges, , and between adjoint charges . We
find that , and our result for the adjoint string
tension is consistent with string breaking.Comment: 10 pages with included figures. For version 2: New calculation and
discussion of latent heat added; 2 new figures and 1 new table. Typo in
abstract corrected for v3. To appear in Physical Review
Properties of the deconfining phase transition in SU(N) gauge theories
We extend our earlier investigation of the finite temperature deconfinement
transition in SU(N) gauge theories, with the emphasis on what happens as N->oo.
We calculate the latent heat in the continuum limit, and find the expected
quadratic in N behaviour at large N. We confirm that the phase transition,
which is second order for SU(2) and weakly first order for SU(3), becomes
robustly first order for N>3 and strengthens as N increases. As an aside, we
explain why the SU(2) specific heat shows no sign of any peak as T is varied
across what is supposedly a second order phase transition. We calculate the
effective string tension and electric gluon masses at T=Tc confirming the
discontinuous nature of the transition for N>2. We explicitly show that the
large-N `spatial' string tension does not vary with T for T<Tc and that it is
discontinuous at T=Tc. For T>Tc it increases as T-squared to a good
approximation, and the k-string tension ratios closely satisfy Casimir Scaling.
Within very small errors, we find a single Tc at which all the k-strings
deconfine, i.e. a step-by-step breaking of the relevant centre symmetry does
not occur. We calculate the interface tension but are unable to distinguish
between linear or quadratic in N variations, each of which can lead to a
striking but different N=oo deconfinement scenario. We remark on the location
of the bulk phase transition, which bounds the range of our large-N
calculations on the strong coupling side, and within whose hysteresis some of
our larger-N calculations are performed.Comment: 50 pages, 14 figure
Precision W-boson and top-quark mass determinations at a muon collider
Precise determinations of the masses of the boson and of the top quark
could stringently test the radiative structure of the Standard Model (SM) or
provide evidence for new physics. We analyze the excellent prospects at a muon
collider for measuring and in the and threshold
regions. With an integrated luminosity of 10 (100) fb, the -boson
mass could be measured to a precision of 20 (6) MeV, and the top-quark mass to
a precision of 200 (70) MeV, provided that theoretical and experimental
systematics are understood. A measurement of MeV for fixed
would constrain a 100 GeV SM Higgs mass within about GeV, while
MeV for fixed would constrain to about GeV.Comment: 27 pages, 11 figures, postscript file available via anonymous
ftp://ucdhep.ucdavis.edu/han/mumu/mwmt.p
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