944 research outputs found
The Spectrum of Open String Field Theory at the Stable Tachyonic Vacuum
We present a level (10,30) numerical computation of the spectrum of quadratic
fluctuations of Open String Field Theory around the tachyonic vacuum, both in
the scalar and in the vector sector. Our results are consistent with Sen's
conjecture about gauge-triviality of the small excitations. The computation is
sufficiently accurate to provide robust evidence for the absence of the photon
from the open string spectrum. We also observe that ghost string field
propagators develop double poles. We show that this requires non-empty BRST
cohomologies at non-standard ghost numbers. We comment about the relations of
our results with recent work on the same subject.Comment: 33 pages, 10 figure
(1+1)-dimensional separation of variables
In this paper we explore general conditions which guarantee that the geodesic
flow on a 2-dimensional manifold with indefinite signature is locally
separable. This is equivalent to showing that a 2-dimensional natural
Hamiltonian system on the hyperbolic plane possesses a second integral of
motion which is a quadratic polynomial in the momenta associated with a
2nd-rank Killing tensor. We examine the possibility that the integral is
preserved by the Hamiltonian flow on a given energy hypersurface only (weak
integrability) and derive the additional requirement necessary to have
conservation at arbitrary values of the Hamiltonian (strong integrability).
Using null coordinates, we show that the leading-order coefficients of the
invariant are arbitrary functions of one variable in the case of weak
integrability. These functions are quadratic polynomials in the coordinates in
the case of strong integrability. We show that for -dimensional systems
there are three possible types of conformal Killing tensors, and therefore,
three distinct separability structures in contrast to the single standard
Hamilton-Jacobi type separation in the positive definite case. One of the new
separability structures is the complex/harmonic type which is characterized by
complex separation variables. The other new type is the linear/null separation
which occurs when the conformal Killing tensor has a null eigenvector.Comment: To appear on Journal of Mathematical Physic
Proof of vanishing cohomology at the tachyon vacuum
We prove Sen's third conjecture that there are no on-shell perturbative
excitations of the tachyon vacuum in open bosonic string field theory. The
proof relies on the existence of a special state A, which, when acted on by the
BRST operator at the tachyon vacuum, gives the identity. While this state was
found numerically in Feynman-Siegel gauge, here we give a simple analytic
expression.Comment: 19 pages, 4 figures; v2: references adde
D-branes as GMS Solitons in Vacuum String Field Theory
In this paper we map the D-brane projector states in the vacuum string field
theory to the noncommutative GMS solitons based on the recently proposed map of
Witten's star to Moyal's star. We find that the singular geometry conditions of
Moore and Taylor are associated with the commutative modes of these projector
states in our framework. The properties of the candidate closed string state
and the wedge state are also discussed, and the possibility of the non-GMS
soliton in VSFT is commented.Comment: 19 pages, LaTex; revised version, typos corrected; third version, a
new subsection about the midpoint singulariy regularization added;fourth
edition, arguments improve
"All on short" prosthetic-implant supported rehabilitations
Objectives. Short implants are increasing their popularity among clinicians who want to fulfill the constant demanding of fixed prosthetic solutions in edentulous jaws. The aim of this report was to propose a new possibility to project and realize an occlusal guided implant cross-arch prosthesis supported by ultra-short implants, describing it presented an edentulous mandible case report. Methods. A 61-year-old, Caucasian, female patient who attended the dental clinic of the University of L’Aquila presented with edentulous posterior inferior jaw and periodontitis and periimplantitis processes in the anterior mandible. The remaining tooth and the affected implant were removed. Six 4-mm-long implants were placed to support a cross-arch metal-resin prosthesis. Results. At 1-year follow-up clinical and radiological assessment showed a good osseointegration of the fixtures and the patient was satisfied with the prosthesis solution. Conclusion. The method, even if it requires further validation, seems to be a valid aid in solving lower edentulous clinical cases, and appears less complex and with more indications of other proposals presented in the current clinical literature. Our case report differs from the current technique All-on-Four, which uses four implants in the mandible to support overdenture prosthesis, assuring a very promising clinical resul
Heterotic String Field Theory
We construct the Neveu-Schwarz sector of heterotic string field theory using
the large Hilbert space of the superghosts and the multi-string products of
bosonic closed string field theory. No picture-changing operators are required
as in Wess-Zumino-Witten-like open superstring field theory. The action
exhibits a novel kind of nonpolynomiality: in addition to terms necessary to
cover missing regions of moduli spaces, new terms arise from the boundary of
the missing regions and its subspaces. We determine the action up to quintic
order and a subset of terms to all orders.Comment: 15 pages, no figures, LaTeX2e; v2: minor cosmetic change
- …