On the Coupling of Gravitons to Matter

Using relationships between open and closed strings, we present a construction of tree-level scattering amplitudes for gravitons minimally coupled to matter in terms of gauge theory partial amplitudes. In particular, we present examples of amplitudes with gravitons coupled to vectors or to a single fermion pair. We also present two examples with massive graviton exchange, as would arise in the presence of large compact dimensions. The gauge charges are represented by flavors of dynamical scalars or fermions. This also leads to an unconventional decomposition of color and kinematics in gauge theories.Comment: RevTex, 4 page

On the homomorphism order of labeled posets

Partially ordered sets labeled with k labels (k-posets) and their homomorphisms are examined. We give a representation of directed graphs by k-posets; this provides a new proof of the universality of the homomorphism order of k-posets. This universal order is a distributive lattice. We investigate some other properties, namely the infinite distributivity, the computation of infinite suprema and infima, and the complexity of certain decision problems involving the homomorphism order of k-posets. Sublattices are also examined.Comment: 14 page

Infrared Optical Conductivity of Bulk Bi₂Te₂Se

id- and near-infrared measurements reveal that the optical conductivity of the three-dimensional topological insulator, Bi₂Te₂Se, is dominated by bulk carriers and shows a linear-in-frequency increase at 0.5 to 0.8 eV. This linearity might be interpreted as a signature of three-dimensional (bulk) Dirac bands; however, band-structure calculations show that transitions between bands with complex dispersion contribute instead to the inter-band optical conductivity at these frequencies and, hence, the observed linearity is accidental. These results warn against the oversimplified interpretations of optical-conductivity measurements in different Dirac materials

Fluctuation corrections to bubble nucleation

The fluctuation determinant which determines the preexponential factor of the transition rate for minimal bubbles is computed for the electroweak theory with $\sin \Theta_W = 0$. As the basic action we use the three-dimensional high-temperature action including, besides temperature dependent masses, the $T \Phi^3$ one-loop contribution which makes the phase transition first order. The results show that this contribution (which has then to be subtracted from the exact result) gives the dominant contribution to the one-loop effective action. The remaining correction is of the order of, but in general larger than the critical bubble action and suppresses the transition rate. The results for the Higgs field fluctuations are compared with those of an approximate heat kernel computation of Kripfganz et al., good agreement is found for small bubbles, strong deviations for large thin-wall bubbles.Comment: 19 pages, LaTeX, no macros, no figure

Metastability of (d+n)-dimensional elastic manifolds

We investigate the depinning of a massive elastic manifold with $d$ internal dimensions, embedded in a $(d+n)$-dimensional space, and subject to an isotropic pinning potential $V({\bf u})=V(|{\bf u}|).$ The tunneling process is driven by a small external force ${\bf F}.$ We find the zero temperature and high temperature instantons and show that for the case $1\le d\le 6$ the problem exhibits a sharp transition from quantum to classical behavior: At low temperatures $T<T_{c}$ the Euclidean action is constant up to exponentially small corrections, while for $T> T_{c},$ ${S_{\rm Eucl}(d,T)}/{\hbar} = {U(d)}/{T}.$ The results are universal and do not depend on the detailed shape of the trapping potential $V({\bf u})$. Possible applications of the problem to the depinning of vortices in high-$T_{c}$ superconductors and nucleation in $d$-dimensional phase transitions are discussed. In addition, we determine the high-temperature asymptotics of the preexponential factor for the $(1+1)$-dimensional problem.Comment: RevTeX, 10 pages, 3 figures inserte

Bosonization of current-current interactions

We discuss a generalization of the conventional bosonization procedure to the case of current-current interactions which get their natural representation in terms of current instead of fermion number density operators. A consistent bosonization procedure requires a geometrical quantization of the hamiltonian action of $W_\infty$ on its coadjoint orbits. An integrable example of a nontrivial realization of this symmetry is presented by the Calogero-Sutherland model. For an illustrative nonintegrable example we consider transverse gauge interactions and calculate the fermion Green function.Comment: 15 pages, TeX, C Version 3.0, Princeton preprin