1,095 research outputs found
Polarized Structure Functions in QCD
We review the nucleon's polarized structure functions from the viewpoint of
gauge invariant, nonlocal light-cone operators in QCD. We discuss a systematic
treatment of the polarized structure functions and the corresponding parton
distribution functions. We also address a question of what information on the
structure of Nature will be obtained from the future polarized experiments.
From this point of view, we will discuss the W gamma production at RHIC
polarized experiment.Comment: 8 pages, 5 Postscript figures, Invited talk presented at the Workshop
on Lepton Scattering, Hadrons and QCD, Adelaide, March 26 -- April 6, 200
Electroweak Sudakov at two loop level
We investigate the Sudakov double logarithmic corrections to the form factor
of fermion in the SU(2)XU(1) electroweak theory. We adopt the familiar Feynman
gauge and present explicit calculations at the two loop level. We show that the
leading logarithmic corrections coming from the infrared singularities are
consistent with the "postulated" exponentiated electroweak Sudakov form factor.
The similarities and differences in the "soft" physics between the electroweak
theory and the unbroken non-abelian gauge theory (QCD) will be clarified.Comment: 8 pages, 14 figure
Transversely Polarized Drell-Yan Process and Soft Gluon Resummation in QCD
We calculate the transverse-momentum spectrum of the dilepton in the
transversely polarized Drell-Yan process on the basis of the factorization
theorem in QCD. We take into account universal logarithmically enhanced
corrections in edge region of phase space by resumming multiple soft-gluon
emissions to all orders in the small region.Comment: 84 pages, 5 figures, Revised version published in Prog.Theor.Phy
Revisiting W gamma production at RHIC
We discuss W gamma production in polarized p p collisions at RHIC energy. We
point out that the RHIC collider has two advantages over other hadron colliders
to measure the characteristic feature of W gamma production: (1) the RHIC
energy is not so high and (2) the polarized beams are available. We calculate
the tree level cross section for W gamma production using a generic spin basis
for W and discuss both the angular dependence and spin correlation.Comment: 14 pages, 15 Postscript figure
Galaxies Inside Stromgren Spheres of Luminous Quasars at z>6: Detection of The First Galaxies
The intrinsic Lyman-alpha emission lines of normal galaxies before
reionization are much absorbed by the damping wing of the Gunn-Peterson trough,
rendering their direct detection nearly impossible, if their intrinsic line
widths are less than ~100km/s. High redshift luminous quasars prior to the
completion of cosmological reionization at z~6, on the other hand, are capable
of producing large HII regions around them (Stromgren spheres) to allow their
intrinsic Lyman-alpha emission lines to be transmitted without overwhelming
absorption (Cen & Haiman 2000). We suggest that targeted observations at the
Stromgren spheres of known luminous quasars at z >= 6 would be able to detect
Lyman-alpha emission lines of galaxies inside the Stromgren spheres largely
unattenuated. A tunable, very narrowband filter of \Delta\lambda\over \lambda ~
0.1% or a narrowband filter of \Delta\lambda\over \lambda ~1% with follow-up
spectroscopic identifications will be required. Such observations could
directly observe the sources of cosmological reionization including possibly
the Pop III galaxies at z=6-20 by JWST. Possible applications include
determinations of the ionization state of the intergalactic medium, the sizes
of the Stromgren spheres, the ages of the quasars, the luminosity function of
high redshift galaxies and its evolution, the spatial distribution of galaxies
and its evolution, the biased distribution of galaxies around quasars and the
anisotropy of quasar emission. Observations using Keck-class telescopes may
already be made to enable a differentiation between a fully neutral and a 10%
neutral intergalactic medium at z>6.Comment: Submitted to ApJ Letters, 10 page
The Major Sources of the Cosmic Reionizing Background at z ~ 6
In this paper, we address which sources contributed most of the reionizing
photons. Our argument assumes that the reionization ended around z ~ 6 and that
it was a relatively quick process, i.e., that there was a non-negligible
fraction of neutral hydrogen in the Universe at somewhat earlier epochs.
Starting from our earlier estimate of the luminosity function (LF) of galaxies
at z ~ 6, we quantitatively show that the major sources of reionization are
most likely galaxies with L < L*. Our approach allows us to put stronger
constraints to the LF of galaxies at z ~ 6. To have the Universe completely
ionized at this redshift, the faint-end slope of the LF should be steeper than
, which is the value measured at lower redshifts (z ~ 3), unless
either the normalization (Phi*) of the LF or the clumping factor of the ionized
hydrogen has been significantly underestimated. If Phi* is actually lower than
what we assumed by a factor of two, a steep slope close to is
required. Our LF predicts a total of 50 -- 80 z ~ 6 galaxies in the HST Ultra
Deep Field (UDF) to a depth of AB=28.4 mag, which can be used to constraint
both Phi* and . We conclude that the least luminous galaxies existing
at this redshift should reach as low as some critical luminosity in order to
accumulate the entire reionizing photon budget. On the other hand, the
existence of significant amounts of neutral hydrogen at slightly earlier
epochs, e.g. z ~ 7, requires that the least luminous galaxies should not be
fainter than another critical value (i.e., the LF should cut-off at this
point).Comment: ApJL in press (Jan 1, 2004 issue
Constraints on First-Light Ionizing Sources from Optical Depth of the Cosmic Microwave Background
We examine the constraints on high-redshift star formation, ultraviolet and
X-ray pre-ionization, and the epoch of reionization at redshift z_r, inferred
from the recent WMAP-5 measurement, tau_e = 0.084 +/- 0.016, of the electron
scattering optical depth of the cosmic microwave background (CMB). Half of this
scattering can be accounted for by the optical depth, tau_e = 0.04-0.05, of a
fully ionized intergalactic medium (IGM) at z < z_GP = 6-7, consistent with
Gunn-Peterson absorption in neutral hydrogen. The required additional optical
depth, Delta-tau_e = 0.03 +/- 0.02 at z > z_GP, constrains the ionizing
contributions of first light sources. WMAP-5 also measured a significant
increase in small-scale power, which lowers the required efficiency of star
formation and ionization from mini-halos. Early massive stars (UV radiation)
and black holes (X-rays) can produce a partially ionized IGM, adding to the
residual electrons left from incomplete recombination. Inaccuracies in
computing the ionization history, x_e(z), and degeneracies in cosmological
parameters (Omega_m, Omega_b, sigma_8, n_s) add systematic uncertainty to the
measurement and modeling of . From the additional optical depth from
sources at z > z_GP, we limit the star-formation efficiency, the rate of
ionizing photon production for Pop III and Pop II stars, and the photon escape
fraction, using standard histories of baryon collapse, minihalo star formation,
and black-hole X-ray preionization.Comment: Greatly revised version, based on WMAP-5 results and new models.
Accepted for ApJ (2008
Extension of holomorphic functions and cohomology classes from non reduced analytic subvarieties
The goal of this survey is to describe some recent results concerning the L 2
extension of holomorphic sections or cohomology classes with values in vector
bundles satisfying weak semi-positivity properties. The results presented here
are generalized versions of the Ohsawa-Takegoshi extension theorem, and borrow
many techniques from the long series of papers by T. Ohsawa. The recent
achievement that we want to point out is that the surjectivity property holds
true for restriction morphisms to non necessarily reduced subvarieties,
provided these are defined as zero varieties of multiplier ideal sheaves. The
new idea involved to approach the existence problem is to make use of L 2
approximation in the Bochner-Kodaira technique. The extension results hold
under curvature conditions that look pretty optimal. However, a major unsolved
problem is to obtain natural (and hopefully best possible) L 2 estimates for
the extension in the case of non reduced subvarieties -- the case when Y has
singularities or several irreducible components is also a substantial issue.Comment: arXiv admin note: text overlap with arXiv:1703.00292,
arXiv:1510.0523
An Overdensity of Lyman-alpha Emitters at Redshift z=5.7 near the Hubble Ultra Deep Field
We have identified an obvious and strong large scale structure at redshift
z=5.75 in a wide (31 by 33 arcminute) field, narrowband survey of the Chandra
Deep Field South region. This structure is traced by 17 candidate Lyman alpha
emitters, among which 12 are found in an 823nm filter (corresponding to Lyman
alpha at z=5.77 +- 0.03) and 5 in an 815nm image (z=5.70 +- 0.03). The Lyman
alpha emitters in both redshift bins are concentrated in one quadrant of the
field. The Hubble Ultra Deep Field, Chandra Deep Field South, and GOODS-South
fields all lie near the edge of this overdense region. Our results are
consistent with reports of an overdensity in the UDF region at z=5.9. This
structure is the highest redshift overdensity found so far.Comment: 12 pages, AASTeX. Submitted to ApJ Letters, and revised in response
to referee's comment
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