1,318 research outputs found
A fresh look at midpoint singularities in the algebra of string fields
In this paper we study the midpoint structure of the algebra of open strings
from the standpoint of the operator/Moyal formalism. We construct a split
string description for the continuous Moyal product of hep-th/0202087, study
the breakdown of associativity in the star algebra, and identify in infinite
sequence of new (anti)commutative coordinates for the star product in in the
complex plane. We also explain how poles in the open string
non(anti)commutativity parameter correspond to certain ``null'' operators which
annihilate the vertex, implying that states proportional to such operators tend
to have vanishing star product with other string fields. The existence of such
poles, we argue, presents an obstruction to realizing a well-defined
formulation of the theory in terms of a Moyal product. We also comment on the
interesting, but singular, representation which has appeared prominently
in the recent studies of Bars {\it et al}.Comment: 40 pages, 5 figures. Version to be submitted to JHEP. Some
interesting and previouusly unpublished results are included here. These
include both an interpretation of poles in the open string noncommutativity
parameter as corresponding to null operators in the algebra, and an
identification of an infinite sequence of new commutative and null
coordinates in the complex plan
Level Truncation and Rolling the Tachyon in the Lightcone Basis for Open String Field Theory
A recent paper by Gross and Erler (hep-th/0406199) showed that by making a
certain well-defined, unitary transformation on the mode basis for the open
bosonic string--one that identifies the lightcone component of position with
the string midpoint--it is possible to render the action for cubic string field
theory local in lightcone time. In this basis, then, cubic string field theory
possesses a well-defined initial value formulation and a conserved Hamiltonian.
With this new understanding it seems natural to study time dependent solutions
representing the the decay of an unstable D-branes. In this paper we study such
solutions using level truncation of mode oscillators in the lightcone basis,
finding both homogenous solutions by perturbatively expanding the string field
in modes , and inhomogenous solutions by integrating the equations of
motion on a lattice. Truncating the theory to level in
oscillators, we find time dependent solutions whose behavior seems
to converge to that of earlier solutions constructed in the center of mass
basis, where the cubic action contains an infinite number of time derivatives.
We further construct time-dependent inhomogeneous solutions including all
fields up to level . These solutions at the outset
display rather erratic behavior due to an unphysical instability introduced by
truncating the theory at the linear level. However upon truncating away the
field responsible for the instability, we find more reasonable solutions which
may possibly represent an approximation to tachyon matter. We conclude with
some discussion of future directions.Comment: 29 pages, 21 figure
The Probability Density of the Higgs Boson Mass
The LEP Collaborations have reported a small excess of events in their
combined Higgs boson analysis at center of mass energies up to about 208 GeV.
In this communication, I present the result of a calculation of the probability
distribution function of the Higgs boson mass which can be rigorously obtained
if the validity of the Standard Model is assumed. It arises from the
combination of the most recent set of precision electroweak data and the
current results of the Higgs searches at LEP 2.Comment: 3 pages, 2 figure
Upper Bound on the Hadronic Light-by-Light Contribution to the Muon g-2
There are indications that hadronic loops in some electroweak observables are
almost saturated by parton level effects. Taking this as the hypothesis for
this work, we propose a genuine parton level estimate of the hadronic
light-by-light contribution to the anomalous magnetic moment of the muon, a_mu
(LBL,had). Our quark mass definitions and values are motivated in detail, and
the simplicity of our approach allows for a transparent error estimate. For
infinitely heavy quarks our treatment is exact, while for asymptotically small
quark masses a_mu (LBL,had) is overestimated. Interpolating, this suggests
quoting an upper bound. We obtain a_mu (LBL,had) < 1.59 10^-9 (95% CL).Comment: 4 pages; 2 references added, some changes in text; final versio
Misfits in Skyrme-Hartree-Fock
We address very briefly five critical points in the context of the
Skyrme-Hartree-Fock (SHF) scheme: 1) the impossibility to consider it as an
interaction, 2) a possible inconsistency of correlation corrections as, e.g.,
the center-of-mass correction, 3) problems to describe the giant dipole
resonance (GDR) simultaneously in light and heavy nuclei, 4) deficiencies in
the extrapolation of binding energies to super-heavy elements (SHE), and 5) a
yet inappropriate trend in fission life-times when going to the heaviest SHE.
While the first two points have more a formal bias, the other three points have
practical implications and wait for solution.Comment: 9 pages, 4 figure
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