51,999 research outputs found
Core-collapse supernovae ages and metallicities from emission-line diagnostics of nearby stellar populations
Massive stars are the main objects that illuminate H II regions and they
evolve quickly to end their lives in core-collapse supernovae (CCSNe). Thus it
is important to investigate the association between CCSNe and H II regions. In
this paper, we present emission line diagnostics of the stellar populations
around nearby CCSNe, that include their host H II regions, from the PMAS/PPAK
Integral-field Supernova hosts COmpilation (PISCO). We then use BPASS stellar
population models to determine the age, metallicity and gas parameters for H II
regions associated with CCSNe, contrasting models that consider either single
star evolution alone or incorporate interacting binaries. We find binary-star
models, that allow for ionizing photon loss, provide a more realistic fit to
the observed CCSN hosts with metallicities that are closer to those derived
from the oxygen abundance in O3N2. We also find that type II and type Ibc SNe
arise from progenitor stars of similar age, mostly from 7 to 45 Myr, which
corresponds to stars with masses < 20 solar mass . However these two types SNe
have little preference in their host environment metallicity measured by oxygen
abundance or in progenitor initial mass. We note however that at lower
metallicities supernovae are more likely to be of type II.Comment: 22 pages, 19 Figures, 6 Tables. Accepted by MNRAS. Comments welcom
Factorization and Unitarity in Superstring Theory
The overall coefficient of the two-loop 4-particle amplitude in superstring
theory is determined by making use of the factorization and unitarity. To
accomplish this we computed in detail all the relevant tree and one-loop
amplitudes involved and determined their overall coefficients in a consistent
way.Comment: LaTex file, 19 pages, 4 figures; v2, minor corrections and figures
corrected; v3, minor corrections with the English, to be published in JHE
Electromagnetic response of high-Tc superconductors -- the slave-boson and doped-carrier theories
We evaluate the doping dependence of the quasiparticle current and low
temperature superfluid density in two slave-particle theories of the tt't''J
model -- the slave-boson theory and doped-carrier theory. In the slave-boson
theory, the nodal quasiparticle current renormalization factor
vanishes proportionally to the zero temperature superfluid density ;
however, we find that away from the limit displays a
much weaker doping dependence than . A similar conclusion applies to
the doped-carrier theory, which differentiates the nodal and antinodal regions
of momentum space. Due to its momentum space anisotropy, the doped-carrier
theory enhances the value of in the hole doped regime, bringing it to
quantitative agreement with experiments, and reproduces the asymmetry between
hole and electron doped cuprate superconductors. Finally, we use the
doped-carrier theory to predict a specific experimental signature of local
staggered spin correlations in doped Mott insulator superconductors which, we
propose, should be observed in STM measurements of underdoped high-Tc
compounds. This experimental signature distinguishes the doped-carrier theory
from other candidate mean-field theories of high-Tc superconductors, like the
slave-boson theory and the conventional BCS theory.Comment: 12 pages, RevTeX4, homepage http://dao.mit.edu/~we
Non-Universality of Transverse Momentum Dependent Parton Distributions at Small-x
We study the universality issue of the transverse momentum dependent parton
distributions at small-x, by comparing the initial/final state interaction
effects in dijet-correlation in pA collisions with those in deep inelastic
lepton nucleus scattering. We demonstrate the non-universality by performing an
explicit calculation in a particular model where the multiple gauge boson
exchange contributions are summed up to all orders. We comment on the
implications of our results on the theoretical interpretation of di-hadron
correlation in dA collisions in terms of the saturation phenomena in deep
inelastic lepton nucleus scattering.Comment: 11 pages, 3 figure
Exact Algorithms for Maximum Independent Set
We show that the maximum independent set problem (MIS) on an -vertex graph
can be solved in time and polynomial space, which even is
faster than Robson's -time exponential-space algorithm
published in 1986. We also obtain improved algorithms for MIS in graphs with
maximum degree 6 and 7, which run in time of and
, respectively. Our algorithms are obtained by using fast
algorithms for MIS in low-degree graphs in a hierarchical way and making a
careful analyses on the structure of bounded-degree graphs
Gapless formation in the condensed color-flavor locked quark matter : a model-independent treatment
The electric/color neutral solution and the critical conditions for gapless
formation are investigated in the condensed color-flavor locked matter.
We point out that there exist no longer gapless modes for down-strange quark
pairing while the gapless phenomenon for up-strange one is dominated in the
condensed environment. In a model-independent way, the phase transition
to the resulting gapless phase is found to be of first-order. The novel phase
structure implies that the chromomagnetic instability happens in the
previous-predicted gapless phase might be removed at least partly.Comment: 2 figure
Driving light pulses with light in two-level media
A two-level medium, described by the Maxwell-Bloch (MB) system, is engraved
by establishing a standing cavity wave with a linearly polarized
electromagnetic field that drives the medium on both ends. A light pulse,
polarized along the other direction, then scatters the medium and couples to
the cavity standing wave by means of the population inversion density
variations. We demonstrate that control of the applied amplitudes of the
grating field allows to stop the light pulse and to make it move backward
(eventually to drive it freely). A simplified limit model of the MB system with
variable boundary driving is obtained as a discrete nonlinear Schroedinger
equation with tunable external potential. It reproduces qualitatively the
dynamics of the driven light pulse
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