4,801 research outputs found
A new geometric approach to problems in birational geometry
A classical set of birational invariants of a variety are its spaces of
pluricanonical forms and some of their canonically defined subspaces. Each of
these vector spaces admits a typical metric structure which is also
birationally invariant. These vector spaces so metrized will be referred to as
the pseudonormed spaces of the original varieties. A fundamental question is
the following: given two mildly singular projective varieties with some of the
first variety's pseudonormed spaces being isometric to the corresponding ones
of the second variety's, can one construct a birational map between them which
induces these isometries? In this work a positive answer to this question is
given for varieties of general type. This can be thought of as a theorem of
Torelli type for birational equivalence.Comment: 13 pages, to appear in PNA
On Kernel Formulas and Dispersionless Hirota Equations
We rederive dispersionless Hirota equations of the dispersionless Toda
hierarchy from the method of kernel formula provided by Carroll and Kodama. We
then apply the method to derive dispersionless Hirota equations of the extended
dispersionless BKP(EdBKP) hierarchy proposed by Takasaki. Moreover, we verify
associativity equations (WDVV equations) in the EdBKP hierarchy from
dispersionless Hirota equations and give a realization of associative algebra
with structure constants expressed in terms of residue formula.Comment: 30 pages, minor corrections, references adde
Decay Constants of Pseudoscalar -mesons in Lattice QCD with Domain-Wall Fermion
We present the first study of the masses and decay constants of the
pseudoscalar mesons in two flavors lattice QCD with domain-wall fermion.
The gauge ensembles are generated on the lattice with the
extent in the fifth dimension, and the plaquette gauge action at , for three sea-quark masses with corresponding pion masses in
the range MeV. We compute the point-to-point quark propagators, and
measure the time-correlation functions of the pseudoscalar and vector mesons.
The inverse lattice spacing is determined by the Wilson flow, while the strange
and the charm quark masses by the masses of the vector mesons
and respectively. Using heavy meson chiral perturbation theory
(HMChPT) to extrapolate to the physical pion mass, we obtain MeV and MeV.Comment: 15 pages, 3 figures. v2: the statistics of ensemble (A) with m_sea =
0.005 has been increased, more details on the systematic error, to appear in
Phys. Lett.
Evolutionary dynamics on any population structure
Evolution occurs in populations of reproducing individuals. The structure of
a biological population affects which traits evolve. Understanding evolutionary
game dynamics in structured populations is difficult. Precise results have been
absent for a long time, but have recently emerged for special structures where
all individuals have the same number of neighbors. But the problem of
determining which trait is favored by selection in the natural case where the
number of neighbors can vary, has remained open. For arbitrary selection
intensity, the problem is in a computational complexity class which suggests
there is no efficient algorithm. Whether there exists a simple solution for
weak selection was unanswered. Here we provide, surprisingly, a general formula
for weak selection that applies to any graph or social network. Our method uses
coalescent theory and relies on calculating the meeting times of random walks.
We can now evaluate large numbers of diverse and heterogeneous population
structures for their propensity to favor cooperation. We can also study how
small changes in population structure---graph surgery---affect evolutionary
outcomes. We find that cooperation flourishes most in societies that are based
on strong pairwise ties.Comment: 68 pages, 10 figure
Magneto-Infrared Spectroscopic Study of Ultrathin BiTe Single Crystals
Ultrathin BiTe single crystals laid on Scotch tape are
investigated by Fourier transform infrared spectroscopy at K and in a
magnetic field up to T. The magneto-transmittance spectra of the Bi%
Te/tape composite are analyzed as a two-layer system and the optical
conductivity of BiTe at different magnetic fields are extracted. We
find that magnetic field modifies the optical conductivity in the following
ways: (1) Field-induced transfer of the optical weight from the lower frequency
regime (cm) to the higher frequency regime (cm) due
to the redistribution of charge carriers across the Fermi surface. (2) Evolving
of a Fano-resonance-like spectral feature from an anti-resonance to a resonance
with increasing magnetic field. Such behavior can be attributed to the
electron-phonon interactions between the optical phonon mode and
the continuum of electronic transitions. (3) Cyclotron resonance resulting from
the inter-valence band Landau level transitions, which can be described by the
electrodynamics of massive Dirac holes
Topological susceptibility in finite temperature QCD with physical domain-wall quarks
We perform hybrid Monte-Carlo (HMC) simulation of lattice QCD with
domain-wall quarks at the physical point, on the lattices, each with three lattice spacings. The lattice
spacings and the bare quark masses are determined on the lattices. The
resulting gauge ensembles provide a basis for studying finite temperature QCD
with domain-wall quarks at the physical point. In this paper, we
determine the topological susceptibility of the QCD vacuum for MeV. The topological charge of each gauge configuration is measured by
the clover charge in the Wilson flow at the same flow time in physical units,
and the topological susceptibility is determined for each
ensemble with lattice spacing and temperature . Using the topological
susceptibility of 15 gauge ensembles with three lattice spacings
and different temperatures in the range MeV, we extract the
topological susceptibility in the continuum limit. Moreover, a
detailed discussion on the reweighting method for domain-wall fermion is
presented.Comment: 36 pages, 5 figure
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