821 research outputs found
A Torsion Correction to the RR 4-Form Fieldstrength
The shifted quantization condition of the M-theory 4-form G_4 is well-known.
The most naive generalization to type IIA string theory fails, an orientifold
counterexample was found by Hori in hep-th/9805141. In this note we use
D2-brane anomaly cancellation to find the corresponding shifted quantization
condition in IIA. Our analysis is consistent with the known O4-plane tensions
if we include a torsion correction to the usual construction of G_4 from C_3, B
and G_2. The resulting Bianchi identities enforce that RR fluxes lift to
K-theory classes.Comment: 10 Pages, 1 eps figur
On the spherical-axial transition in supernova remnants
A new law of motion for supernova remnant (SNR) which introduces the quantity
of swept matter in the thin layer approximation is introduced. This new law of
motion is tested on 10 years observations of SN1993J. The introduction of an
exponential gradient in the surrounding medium allows to model an aspherical
expansion. A weakly asymmetric SNR, SN1006, and a strongly asymmetric SNR,
SN1987a, are modeled. In the case of SN1987a the three observed rings are
simulated.Comment: 19 figures and 14 pages Accepted for publication in Astrophysics &
Space Science in the year 201
Nongeometric Flux Compactifications
We investigate a simple class of type II string compactifications which
incorporate nongeometric "fluxes" in addition to "geometric flux" and the usual
H-field and R-R fluxes. These compactifications are nongeometric analogues of
the twisted torus. We develop T-duality rules for NS-NS geometric and
nongeometric fluxes, which we use to construct a superpotential for the
dimensionally reduced four-dimensional theory. The resulting structure is
invariant under T-duality, so that the distribution of vacua in the IIA and IIB
theories is identical when nongeometric fluxes are included. This gives a
concrete framework in which to investigate the possibility that generic string
compactifications may be nongeometric in any duality frame. The framework
developed in this paper also provides some concrete hints for how mirror
symmetry can be generalized to compactifications with arbitrary H-flux, whose
mirrors are generically nongeometric.Comment: 26 pages, JHEP3. v3: references, minor corrections, and
clarifications added. v4: sign correcte
Type IIA Moduli Stabilization
We demonstrate that flux compactifications of type IIA string theory can
classically stabilize all geometric moduli. For a particular orientifold
background, we explicitly construct an infinite family of supersymmetric vacua
with all moduli stabilized at arbitrarily large volume, weak coupling, and
small negative cosmological constant. We obtain these solutions from both
ten-dimensional and four-dimensional perspectives. For more general
backgrounds, we study the equations for supersymmetric vacua coming from the
effective superpotential and show that all geometric moduli can be stabilized
by fluxes. We comment on the resulting picture of statistics on the landscape
of vacua.Comment: 48 pages, 2 figures, LaTeX. v2: references added. v3: minor comments
& references adde
Primordialists and Constructionists: a typology of theories of religion
This article adopts categories from nationalism theory to classify theories of religion. Primordialist explanations are grounded in evolutionary psychology and emphasize the innate human demand for religion. Primordialists predict that religion does not decline in the modern era but will endure in perpetuity. Constructionist theories argue that religious demand is a human construct. Modernity initially energizes religion, but subsequently undermines it. Unpacking these ideal types is necessary in order to describe actual theorists of religion. Three distinctions within primordialism and constructionism are relevant. Namely those distinguishing: a) materialist from symbolist forms of constructionism; b) theories of origins from those pertaining to the reproduction of religion; and c) within reproduction, between theories of religious persistence and secularization. This typology helps to make sense of theories of religion by classifying them on the basis of their causal mechanisms, chronology and effects. In so doing, it opens up new sightlines for theory and research
Exclusion limits on the WIMP-nucleon cross-section from the Cryogenic Dark Matter Search
The Cryogenic Dark Matter Search (CDMS) employs low-temperature Ge and Si
detectors to search for Weakly Interacting Massive Particles (WIMPs) via their
elastic-scattering interactions with nuclei while discriminating against
interactions of background particles. For recoil energies above 10 keV, events
due to background photons are rejected with >99.9% efficiency, and surface
events are rejected with >95% efficiency. The estimate of the background due to
neutrons is based primarily on the observation of multiple-scatter events that
should all be neutrons. Data selection is determined primarily by examining
calibration data and vetoed events. Resulting efficiencies should be accurate
to about 10%. Results of CDMS data from 1998 and 1999 with a relaxed
fiducial-volume cut (resulting in 15.8 kg-days exposure on Ge) are consistent
with an earlier analysis with a more restrictive fiducial-volume cut.
Twenty-three WIMP candidate events are observed, but these events are
consistent with a background from neutrons in all ways tested. Resulting limits
on the spin-independent WIMP-nucleon elastic-scattering cross-section exclude
unexplored parameter space for WIMPs with masses between 10-70 GeV c^{-2}.
These limits border, but do not exclude, parameter space allowed by
supersymmetry models and accelerator constraints. Results are compatible with
some regions reported as allowed at 3-sigma by the annual-modulation
measurement of the DAMA collaboration. However, under the assumptions of
standard WIMP interactions and a standard halo, the results are incompatible
with the DAMA most likely value at >99.9% CL, and are incompatible with the
model-independent annual-modulation signal of DAMA at 99.99% CL in the
asymptotic limit.Comment: 40 pages, 49 figures (4 in color), submitted to Phys. Rev. D;
v.2:clarified conclusions, added content and references based on referee's
and readers' comments; v.3: clarified introductory sections, added figure
based on referee's comment
Tensor Correlations Measured in 3He(e,e'pp)n
We have measured the 3He(e,e'pp)n reaction at an incident energy of 4.7 GeV
over a wide kinematic range. We identified spectator correlated pp and pn
nucleon pairs using kinematic cuts and measured their relative and total
momentum distributions. This is the first measurement of the ratio of pp to pn
pairs as a function of pair total momentum, . For pair relative
momenta between 0.3 and 0.5 GeV/c, the ratio is very small at low and
rises to approximately 0.5 at large . This shows the dominance of
tensor over central correlations at this relative momentum.Comment: 4 pages, 4 figures, submitted to PR
Demonstration of a novel technique to measure two-photon exchange effects in elastic scattering
The discrepancy between proton electromagnetic form factors extracted using
unpolarized and polarized scattering data is believed to be a consequence of
two-photon exchange (TPE) effects. However, the calculations of TPE corrections
have significant model dependence, and there is limited direct experimental
evidence for such corrections. We present the results of a new experimental
technique for making direct comparisons, which has the potential to
make precise measurements over a broad range in and scattering angles. We
use the Jefferson Lab electron beam and the Hall B photon tagger to generate a
clean but untagged photon beam. The photon beam impinges on a converter foil to
generate a mixed beam of electrons, positrons, and photons. A chicane is used
to separate and recombine the electron and positron beams while the photon beam
is stopped by a photon blocker. This provides a combined electron and positron
beam, with energies from 0.5 to 3.2 GeV, which impinges on a liquid hydrogen
target. The large acceptance CLAS detector is used to identify and reconstruct
elastic scattering events, determining both the initial lepton energy and the
sign of the scattered lepton. The data were collected in two days with a
primary electron beam energy of only 3.3 GeV, limiting the data from this run
to smaller values of and scattering angle. Nonetheless, this measurement
yields a data sample for with statistics comparable to those of the
best previous measurements. We have shown that we can cleanly identify elastic
scattering events and correct for the difference in acceptance for electron and
positron scattering. The final ratio of positron to electron scattering:
for GeV and
Measurement of the nuclear multiplicity ratio for hadronization at CLAS
The influence of cold nuclear matter on lepto-production of hadrons in
semi-inclusive deep inelastic scattering is measured using the CLAS detector in
Hall B at Jefferson Lab and a 5.014 GeV electron beam. We report the
multiplicity ratios for targets of C, Fe, and Pb relative to deuterium as a
function of the fractional virtual photon energy transferred to the
and the transverse momentum squared of the . We find that the
multiplicity ratios for are reduced in the nuclear medium at high
and low , with a trend for the transverse momentum to be
broadened in the nucleus for large .Comment: Submitted to Phys. Lett.
Precise Measurements of Beam Spin Asymmetries in Semi-Inclusive production
We present studies of single-spin asymmetries for neutral pion
electroproduction in semi-inclusive deep-inelastic scattering of 5.776 GeV
polarized electrons from an unpolarized hydrogen target, using the CEBAF Large
Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator
Facility. A substantial amplitude has been measured in the
distribution of the cross section asymmetry as a function of the azimuthal
angle of the produced neutral pion. The dependence of this amplitude
on Bjorken and on the pion transverse momentum is extracted with
significantly higher precision than previous data and is compared to model
calculations.Comment: to be submitted PL
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