561 research outputs found
Twisted Supersymmetric Gauge Theories and Orbifold Lattices
We examine the relation between twisted versions of the extended
supersymmetric gauge theories and supersymmetric orbifold lattices. In
particular, for the SYM in , we show that the continuum
limit of orbifold lattice reproduces the twist introduced by Marcus, and the
examples at lower dimensions are usually Blau-Thompson type. The orbifold
lattice point group symmetry is a subgroup of the twisted Lorentz group, and
the exact supersymmetry of the lattice is indeed the nilpotent scalar
supersymmetry of the twisted versions. We also introduce twisting in terms of
spin groups of finite point subgroups of -symmetry and spacetime symmetry.Comment: 32 page
The minimal supersymmetric model without a mu term
We propose a supersymmetric extension of the standard model which is a realistic alternative to the MSSM, and which has several advantages. No 'mu' supersymmetric Higgs/Higgsino mass parameter is needed for sufficiently heavy harginos. An approximate U(1)(R) symmetry naturally guarantees that tan beta is large, explaining the top/bottom quark mass hierarchy. This symmetry also suppresses supersymmetric contributions to anomalous magnetic moments, b --> sgamma, and proton decay, and these processes place no lower bounds on superpartner masses, even at large tan beta. The soft supersymmetry breaking mass parameters can easily be obtained from either gauge or Planck scale mediation, without the usual mu problem. Unlike in the MSSM, there are significant upper bounds on the masses of superpartners, including an upper bound of 114 GeV on the mass of the lightest chargino. However the MSSM bound on the lightest Higgs mass does not apply
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
Hardware transactional memory with software-defined conflicts
In this paper we propose conflict-defined blocks, a programming language construct that allows programmers to change the concept of conflict from one transaction to another, or even throughout the course of the same transaction. Defining conflicts in software makes possible the removal of dependencies which, though not necessary for the correct execution of the transactions, arise as a result of the coarse synchronization style encouraged by TM. Programmers take advantage of their knowledge about the problem and specify through confict-defined blocks what types of dependencies are superfluous in a certain part of the transaction, in order to extract more performance out of coarse-grained transactions without having to write minimally synchronized code. Our experiments with several transactional benchmarks reveal that using software-defined conflicts, the programmer achieves significant reductions in the number of aborted transactions and improve scalability.Peer ReviewedPostprint (author's final draft
Towards lattice simulation of the gauge theory duals to black holes and hot strings
A generalization of the AdS/CFT conjecture postulates a duality between IIA
string theory and 16 supercharge Yang-Mills quantum mechanics in the large N 't
Hooft limit. At low temperatures string theory describes black holes, whose
thermodynamics may hence be studied using the dual quantum mechanics. This
quantum mechanics is strongly coupled which motivates the use of lattice
techniques. We argue that, contrary to expectation, the theory when discretized
naively will nevertheless recover continuum supersymmetry as the lattice
spacing is sent to zero. We test these ideas by studying the 4 supercharge
version of this Yang-Mills quantum mechanics in the 't Hooft limit. We use both
a naive lattice action and a manifestly supersymmetric action. Using Monte
Carlo methods we simulate the Euclidean theories, and study the lattice
continuum limit, for both thermal and non-thermal periodic boundary conditions,
confirming continuum supersymmetry is recovered for the naive action when
appropriate. We obtain results for the thermal system with N up to 12. These
favor the existence of a single deconfined phase for all non-zero temperatures.
These results are an encouraging indication that the 16 supercharge theory is
within reach using similar methods and resources.Comment: 49 pages, 14 figure
Integrable Spin Chains on the Conformal Moose
We consider N=1, D=4 superconformal U(N)^{pq} Yang-Mills theories dual to
AdS_5xS^5/Z_pxZ_q orbifolds. We construct the dilatation operator of this
superconformal gauge theory at one-loop planar level. We demonstrate that a
specific sector of this dilatation operator can be thought of as the transfer
matrix for a two-dimensional statistical mechanical system, related to an
integrable SU(3) anti-ferromagnetic spin chain system, which in turn is
equivalent to a 2+1-dimensional string theory where the spatial slices are
discretized on a triangular lattice. This is an extension of the SO(6) spin
chain picture of N=4 super Yang-Mills theory. We comment on the integrability
of this N=1 gauge theory and hence the corresponding three-dimensional
statistical mechanical system, its connection to three-dimensional lattice
gauge theories, extensions to six-dimensional string theories, AdS/CFT type
dualities and finally their construction via orbifolds and brane-box models. In
the process we discover a new class of almost-BPS BMN type operators with large
engineering dimensions but controllably small anomalous corrections.Comment: 53 pages, 14 eps figures; Added reference
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