43,189 research outputs found
Portrait of the String as a Random Walk
In this paper we analyze a Rutherford type experiment where light probes are
inelastically scattered by an ensemble of excited closed strings, and use the
corresponding cross section to extract density-density correlators between
different pieces of the target string. We find a wide dynamical range where the
space-time evolution of typical highly excited closed strings is accurately
described as a convolution of brownian motions. Moreover, we show that if we
want to obtain the same cross section by coherently scattering probes off a
classical background, then this background has to be time-dependent and
singular. This provides an example where singularities arise, not as a result
of strong gravitational self-interactions, but as a byproduct of the
decoherence implicit in effectively describing the string degrees of freedom as
a classical background.Comment: 17 pages. Typos corrected, 1 reference adde
Generalized effective hamiltonian for graphene under non-uniform strain
We use a symmetry approach to construct a systematic derivative expansion of
the low energy effective Hamiltonian modifying the continuum Dirac description
of graphene in the presence of non-uniform elastic deformations. We extract all
experimentally relevant terms and describe their physical significance. Among
them there is a new gap-opening term that describes the Zeeman coupling of the
elastic pseudomagnetic field and the pseudospin. We determine the value of the
couplings using a generalized tight binding model.Comment: 13 pages, 1 figure. Matches published version + 1 footnote added,
typos correcte
- …