Gravitational Mediation of Supersymmetry Breaking in Superstring Theory

SUSY breaking and its mediation are among the most important problems of supersymmetric generalizations of the standard model. The idea of gravity-mediated SUSY breaking, proposed in 1982 by Arnowitt, Chamseddine and Nath, and independently by Barbieri, Ferrara and Savoy, fits naturally into superstring theory, where it can be realized at both classical as well as quantum levels. This talk is dedicated to Pran Nath on his 65th birthday.Comment: 8 pages. Dedicated to Pran Nath on his 65th birthda

Surface properties of the clean and Au/Pd covered Fe3_3O4_4(111): a DFT and DFT+UU study

The spin-density functional theory (DFT) and DFT+$U$ with Hubbard $U$ term accounting for on-site Coulomb interactions were applied to investigate structure, stability, and electronic properties of different terminations of the Fe$_3$O$_4$(111) surface. All terminations of the ferrimagnetic Fe$_3$O$_4$(111) surface exhibit very large (up to 90%) relaxations of the first four interlayer distances, decreasing with the oxide layer depth. Our calculations predict the iron terminated surface to be most stable in a wide range of the accessible values of the oxygen chemical potential. The adsorption of Au and Pd on two stable Fe- and O-terminated surfaces is studied. Our results show that Pd binds stronger than Au both to the Fe- and O-terminated surface. DFT+$U$ gives stronger bonding than DFT. The bonding of both adsorbates to the O-terminated magnetite surface is by 1.5-2.5 eV stronger than to the Fe-terminated surface

Graviton Amplitudes from Collinear Limits of Gauge Amplitudes

We express all tree-level graviton amplitudes in Einstein's gravity as the collinear limits of a linear combination of pure Yang-Mills amplitudes in which each graviton is represented by two gauge bosons, each of them carrying exactly one half of graviton's momentum and helicity.Comment: 7 pages, harvma

Graviton as a Pair of Collinear Gauge Bosons

We show that the mixed gravitational/gauge superstring amplitudes describing decays of massless closed strings - gravitons or dilatons - into a number of gauge bosons, can be written at the tree (disk) level as linear combinations of pure open string amplitudes in which the graviton (or dilaton) is replaced by a pair of collinear gauge bosons. Each of the constituent gauge bosons carry exactly one half of the original closed string momentum, while their +/- 1 helicities add up to +/- 2 for the graviton or to 0 for the dilaton.Comment: 10 pages, harvmac; v2: references adde