Spectral geometry for strings and branes

I give a short guide into applications of the heat kernel technique to string/brane physics with an emphasis on the emerging boundary value problems.Comment: A talk at "Quantum Gravity and Spectral Geometry", Naples, July 2001, to appear in the Proceeding

An Equivalence Between Momentum and Charge in String Theory

It is shown that for a translationally invariant solution to string theory, spacetime duality interchanges the momentum in the symmetry direction and the axion charge per unit length. As one application, we show explicitly that charged black strings are equivalent to boosted (uncharged) black strings. The extremal black strings (which correspond to the field outside of a fundamental macroscopic string) are equivalent to plane fronted waves describing strings moving at the speed of light.Comment: 10 page

Unifying gauge couplings at the string scale

Using the current precision electroweak data, we look for the minimal particle content which is necessary to add to the standard model in order to have a complete unification of gauge couplings and gravity at the weakly coupled heterotic string scale. We find that the addition of a vector-like fermion at an intermediate scale and a non-standard hypercharge normalization are in general sufficient to achieve this goal at two-loop level. Requiring the extra matter scale to be below the TeV scale, it is found that the addition of three vector-like fermion doublets with a mass around 700 GeV yields a perfect string-scale unification, provided that the affine levels are $(k_Y, k_2 ,k_3)=(13/3, 1, 2)$, as in the $SU(5) \times SU(5)$ string-GUT. Furthermore, if supersymmetry is broken at the unification scale, the Higgs mass is predicted in the range 125 GeV - 170 GeV, depending on the precise values of the top quark mass and $\tan \beta$ parameter.Comment: 11 pages, 4 eps figures, using jpconf style, talk given at CORFU2005, RTN meeting ``The Quest for Unification: Theory Confronts Experiment'', 11 - 18 September 2005, Corfu, Greec

Nonsingular 2-D Black Holes and Classical String Backgrounds

We study a string-inspired classical 2-D effective field theory with {\it nonsingular} black holes as well as Witten's black hole among its static solutions. By a dimensional reduction, the static solutions are related to the $(SL(2,R)_{k}\otimes U(1))/U(1)$ coset model, or more precisely its $O\bigl((\alpha')^{0}\bigr)$ approximation known as the 3-D charged black string. The 2-D effective action possesses a propagating degree of freedom, and the dynamics are highly nontrivial. A collapsing shell is shown to bounce into another universe without creating a curvature singularity on its path, and the potential instability of the Cauchy horizon is found to be irrelevent in that some of the infalling observers never approach the Cauchy horizon. Finally a $SL(2,R)_{k}/U(1)$ nonperturbative coset metric, found and advocated by R. Dijkgraaf et.al., is shown to be nonsingular and to coincide with one of the charged spacetimes found above. Implications of all these geometries are discussed in connection with black hole evaporation.Comment: 30 pages with 2 figures, harvmac, CALT-68-1852 (Discussions on the gravitational collapse of thin shells in a charged spacetime are clarified. Two extra references.

Rotating Dilaton Black Holes

It is shown that an arbitrarily small amount of angular momentum can qualitatively change the properties of extremal charged black holes coupled to a dilaton. In addition, the gyromagnetic ratio of these black holes is computed and an exact rotating black string solution is presented.Comment: 14 page

Exact Models of Extremal Dyonic 4D Black Hole Solutions of Heterotic String Theory

Families of exact $(0,2)$ supersymmetric conformal field theories of magnetically and electrically charged extremal 4D black hole solutions of heterotic string theory are presented. They are constructed using a $(0,1)$ supersymmetric $SL(2,R)\times SU(2)$ WZW model where anomalously embedded $U(1)\times U(1)$ subgroups are gauged. Crucial cancelations of the $U(1)$ anomalies coming from the supersymmetric fermions, the current algebra fermions and the gauging ensure that there is a consistency of these models at the quantum level. Various 2D models, which may be considered as building blocks for extremal 4D constructions, are presented. They generalise the class of 2D models which might be obtained from gauging $SL(2,R)$ and coincide with known heterotic string backgrounds. The exact conformal field theory presented by Giddings, Polchinski and Strominger describing the angular sector of the extremal magnetically charged black hole is a special case of this construction. An example where the radial and angular theories are mixed non--trivially is studied in detail, resulting in an extremal dilatonic Taub--NUT--like dyon.Comment: 42 pages (Plain TEX), IASSNS-HEP-94/20 (Revised version has minor corrections, references and a note added and is now identical to published version in Phys Rev D.

O(d,d) invariance at two and three loops

We show that in a two-dimensional sigma-model whose fields only depend on one target space co-ordinate, the O(d,d) invariance of the conformal invariance conditions observed at one loop is preserved at two loops (in the general case with torsion) and at three loops (in the case without torsion).Comment: 21 pages. Plain Tex. Uses Harvmac ("b" option). Revised Version with references added and minor errors correcte

Two-Vierbein Formalism for String-Inspired Axionic Gravity

Using independent left and right vierbeins to describe graviton plus axion as suggested by string mechanics, O(d,d) duality can be realized linearly.Comment: 14 pg., (uuencoded dvi file; fixed uuencoding so file is unprotected) ITP-SB-93-

The non-uniform, dynamic atmosphere of Betelgeuse observed at mid-infrared wavelengths

We present an interferometric study of the continuum surface of the red supergiant star Betelgeuse at 11.15 microns wavelength, using data obtained with the Berkeley Infrared Spatial Interferometer each year between 2006 and 2010. These data allow an investigation of an optically thick layer within 1.4 stellar radii of the photosphere. The layer has an optical depth of ~1 at 11.15 microns, and varies in temperature between 1900 K and 2800 K and in outer radius between 1.16 and 1.36 stellar radii. Electron-hydrogen atom collisions contribute significantly to the opacity of the layer. The layer has a non-uniform intensity distribution that changes between observing epochs. These results indicate that large-scale surface convective activity strongly influences the dynamics of the inner atmosphere of Betelgeuse, and mass-loss processes.Comment: 13 pages, 5 figures, in press (ApJ

Supersymmetric Quantum Corrections and Poisson-Lie T-Duality

The quantum actions of the (4,4) supersymmetric non-linear sigma model and its dual in the Abelian case are constructed by using the background superfield method. The propagators of the quantum superfield and its dual and the gauge fixing actions of the original and dual (4,4) supersymmetric sigma models are determined. On the other hand, the BRST transformations are used to obtain the quantum dual action of the (4,4) supersymmetric non-linear sigma model in the sense of Poisson-Lie T-dualityComment: 18 page