34 research outputs found
Compactified NCOS and duality
We study four-dimensional U(1) on a non-commutative T^2 with rational Theta.
This theory has dual descriptions as ordinary SYM or as NCOS. We identify a set
of massive non-interacting KK states in the SYM theory and track them through
the various dualities. They appear as stretched strings in the non-commutative
U(1) providing another example of the IR/UV mixing in non-commutative field
theories. In the NCOS these states appear as D-strings with winding and
momentum. They form an unconventional type of 1/4 BPS state with the 3-brane.
To obtain a consistent picture of S-duality for compactified theories it is
essential to keep track of both the NS and the RR B-fields.Comment: 16 pages, references correcte
Thick domain walls and singular spaces
We discuss thick domain walls interpolating between spaces with naked
singularities and give arguments based on the /CFT correspondence why such
singularities may be physically meaningful. Our examples include thick domain
walls with Minkowski, de Sitter, and anti-de Sitter geometries on the
four-dimensional slice. For flat domain walls we can solve the equivalent
quantum mechanics problem exactly, which provides the spectrum of graviton
states. In one of the examples we discuss, the continuum states have a mass
gap. We compare the graviton spectra with expectations from the /CFT
correspondence and find qualitative agreement. We also discuss unitary boundary
conditions and show that they project out all continuum states.Comment: 21 pages, v2: references corrected, v3: minor corrections in sect.
Mirror symmetry for N=1 QED in three dimensions
We construct three-dimensional N=1 QED with N_f flavors using branes of type
IIB string theory. This theory has a mirror, which can be realized using the
S-dual brane configuration. As in examples with more supersymmetry, the Higgs
branch of the original theory gets mapped into the Coulomb branch of the
mirror. We use parity invariance to argue that these branches cannot be lifted
by quantum corrections.Comment: 10 pages, Latex, 1 figure, reference adde
Heterotic Little String Theories and Holography
It has been conjectured that Little String Theories in six dimensions are
holographic to critical string theory in a linear dilaton background. We test
this conjecture for theories arising on the worldvolume of heterotic
fivebranes. We compute the spectrum of chiral primaries in these theories and
compare with results following from Type I-heterotic duality and the AdS/CFT
correspondence. We also construct holographic duals for heterotic fivebranes
near orbifold singularities. Finally we find several new Little String Theories
which have Spin(32)/Z_2 or E_8 \times E_8 global symmetry but do not have a
simple interpretation either in heterotic or M-theory.Comment: 27 pages, LaTe
A Simple Volcano Potential with an Analytic, Zero-Energy, Ground State
We describe a simple volcano potential, which is supersymmetric and has an
analytic, zero-energy, ground state. (The KK modes are also analytic.) It is an
interior harmonic oscillator potential properly matched to an exterior angular
momentum-like tail. Special cases are given to elucidate the physics, which may
be intuitively useful in studies of higher-dimensional gravity.Comment: 8 pages, 3 figure
Order 1/m_b^3 corrections to B\to X_c\ell\bar\nu decay and their implication for the measurement of \bar\Lambda and \lambda_1
We compute the order 1/m_b^3 nonperturbative contributions to the inclusive
differential B\to X_c\ell\bar\nu decay rate. They are parametrized by the
expectation values of two local and four nonlocal dimension-six operators. We
use our results to estimate part of the theoretical uncertainties in the
extraction of matrix elements \bar\Lambda and \lambda_1 from the lepton
spectrum in the inclusive semileptonic B decay and find them to be very large.
We also compute the 1/m_b^3 corrections to the moments of the hadronic
invariant mass spectrum in this decay, and combine them with the extracted
values of \bar\Lambda and \lambda_1 to put an upper bound on the branching
fraction Br(B\to D^{**}\ell\bar\nu).Comment: 21 pages, revtex, 2 postscript figures. Section on the
nonrelativistic quark model estimates is removed; some points of the
computation are clarified; results unchange
Aspects of Heavy Quark Physics
We discuss the use of two QCD based effective field theories in determining parameters
of the standard model. Heavy Quark Effective theory provides a framework for
studying the weak decays of the B meson. We calculate the B → Xclv decay rate
to second nonvanishing order in the HQET expansion and compare the theoretical
prediction to experimental data. This allows us to determine the b and c pole quark
masses and the weak mixing angle Vcb.
Nonrelativistic QCD is an effective field theory in which bound states of two heavy
quarks can be analyzed conveniently. We use this approach to compute the leading
relativistic corrections to the decay of S-wave quarkonia. These corrections can be
expressed in terms of the leading order result and the quark pole mass. Including
color octet contributions and the first relativistic corrections, we extract the value
of αs from low energy data. We also show that the color octet contributions to the
decay rates are not negligible.</p