9,974 research outputs found
Abelian Hurwitz-Hodge integrals
Hodge classes on the moduli space of admissible covers with monodromy group G are
associated to irreducible representations of G. We evaluate all linear Hodge integrals over moduli
spaces of admissible covers with abelian monodromy in terms of multiplication in an associated
wreath group algebra. In case G is cyclic and the representation is faithful, the evaluation is in terms
of double Hurwitz numbers. In case G is trivial, the formula specializes to the well-known result
of Ekedahl-Lando-Shapiro-Vainshtein for linear Hodge integrals over the moduli space of curves in
terms of single Hurwitz number
Fast-Light in a Photorefractive Crystal for Gravitational Wave Detection
We demonstrate superluminal light propagation using two frequency multiplexed
pump beams to produce a gain doublet in a photorefractive crystal of Ce:BaTiO3.
The two gain lines are obtained by two-wave mixing between a probe field and
two individual pump fields. The angular frequencies of the pumps are
symmetrically tuned from the frequency of the probe. The frequency difference
between the pumps corresponds to the separation of the two gain lines; as it
increases, the crystal gradually converts from normal dispersion without
detuning to an anomalously dispersive medium. The time advance is measured as
0.28 sec for a pulse propagating through a medium with a 2Hz gain separation,
compared to the same pulse propagating through empty space. We also demonstrate
directly anomalous dispersion profile using a modfied experimental
configuration. Finally, we discuss how anomalous dispersion produced this way
in a faster photorefractive crystal (such as SPS: Sn2P2S6) could be employed to
enhance the sensitivity-bandwidth product of a LIGO type gravitational wave
detector augmented by a White Light Cavity.Comment: 14 pages, 5 figure
NbSe3: Effect of Uniaxial Stress on the Threshold Field and Fermiology
We have measured the effect of uniaxial stress on the threshold field ET for
the motion of the upper CDW in NbSe3. ET exhibits a critical behavior, ET ~ (1
- e/ec)^g, wher e is the strain, and ec is about 2.6% and g ~ 1.2. This
ecpression remains valid over more than two decades of ET, up to the highest
fields of about 1.5keV/m. Neither g nor ec is very sensitive to the impurity
concentraction. The CDW transition temperature Tp decreases linearly with e at
a rate dTp/de = -10K/%, and it does not show any anomaly near ec. Shubnikov
de-Haas measurements show that the extremal area of the Fermi surface decreases
with increasing strain. The results suggest that there is an intimate
relationship between pinning of the upper CDW and the Fermiology of NbSe3.Comment: 4 pages, 5 figure
Effect of Crystallization of the Grain-Boundary Phase on the Thermal Diffusivity of a Sialon Ceramic
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65865/1/j.1151-2916.1984.tb19519.x.pd
Graded index and randomly oriented core-shell silicon nanowires with broadband and wide angle antireflection
Antireflection with broadband and wide angle properties is important for a wide range of applications on photovoltaic cells and display. The SiOx shell layer provides a natural antireflection from air to the Si core absorption layer. In this work, we have demonstrated the random core-shell silicon nanowires with both broadband (from 400nm to 900nm) and wide angle (from normal incidence to 60o) antireflection characteristics within AM1.5 solar spectrum. The graded index structure from the randomly oriented core-shell (Air/SiOx/Si) nanowires may provide a potential avenue to realize a broadband and wide angle antireflection laye
Gamma-ray Constraints on Effective Interactions of the Dark Matter
Using an effective interaction approach to describe the interactions between
the dark matter particle and the light degrees of freedom of the standard
model, we calculate the gamma-ray flux due to the annihilation of the dark
matter into quarks, followed by fragmentation into neutral pions which
subsequently decay into photons. By comparison to the mid-latitude data
released from the Fermi-LAT experiment, we obtain useful constraints on the
size of the effective interactions and they are found to be comparable to those
deduced from collider, gamma-ray line and anti-matter search experiments.
However, the two operators induced by scalar and vector exchange among
fermionic dark matter and light quarks that contribute to spin-independent
cross sections are constrained more stringently by the recent XENON100 data.Comment: 22 pages, 4 figures; title fixed and a couple of references adde
SL(2,Z) Multiplets in N=4 SYM Theory
We discuss the action of SL(2,Z) on local operators in D=4, N=4 SYM theory in
the superconformal phase. The modular property of the operator's scaling
dimension determines whether the operator transforms as a singlet, or
covariantly, as part of a finite or infinite dimensional multiplet under the
SL(2,Z) action. As an example, we argue that operators in the Konishi multiplet
transform as part of a (p,q) PSL(2,Z) multiplet. We also comment on the
non-perturbative local operators dual to the Konishi multiplet.Comment: 14 pages, harvmac; v2: published version with minor change
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