916 research outputs found
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
Conifold geometries, topological strings and multi-matrix models
We study open B-model representing D-branes on 2-cycles of local Calabi--Yau
geometries. To this end we work out a reduction technique linking D-branes
partition functions and multi-matrix models in the case of conifold geometries
so that the matrix potential is related to the complex moduli of the conifold.
We study the geometric engineering of the multi-matrix models and focus on
two-matrix models with bilinear couplings. We show how to solve this models in
an exact way, without resorting to the customary saddle point/large N
approximation. The method consists of solving the quantum equations of motion
and using the flow equations of the underlying integrable hierarchy to derive
explicit expressions for correlators. Finally we show how to incorporate in
this formalism the description of several group of D-branes wrapped around
different cycles.Comment: 35 pages, 5.3 and 6 revise
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
The Discovery of Two Lyman Emitters Beyond Redshift 6 in the Subaru Deep Field
We have performed a deep optical imaging survey using a narrowband filter
() centered at 9196 \AA ~ together with and
broadband filters covering an 814 arcmin area of the Subaru Deep
Field. We obtained a sample of 73 strong -excess objects based on the
following two color criteria; and . We then obtained optical spectroscopy of nine objects in our
-excess sample, and identified at least two Ly emitters
at and , each of which shows the
characteristic sharp cutoff together with the continuum depression at
wavelengths shortward of the line peak. The latter object is more distant than
HCM-6A at and thus this is the most distant known object found so far.
These new data allow us to estimate the first meaningful lower limit of the
star formation rate density beyond redshift 6; yr Mpc. Since it is expected that the actual
density is higher by a factor of several than this value, our new observation
reveals that a moderately high level of star formation activity already
occurred at 6.6.Comment: 13 pages, 3 figures. PASJ (Letters), 55, vol.2, in pres
Shakhbazian compact galaxy groups. II. Photometric and spectroscopic study of ShCG 376
The results of the redshift measurements and of the detailed surface
photometry in BVR of the compact group ShCG 376 are presented. The radial
velocity dispersion, the virial mass, the total luminosity, the M/L ratio, and
the crossing time of the group are estimated. The group consists of eight
accordant redshift spiral galaxies. Four (or possibly five) of the group
members have emission-line spectra. Such morphological content and the number
of emission-line galaxies are very atypical for compact galaxy groups. There
are signs of interaction between some members of the group. It is suggested
that the irregular shape of the brightest galaxy No. 4 is probably due to
interaction with other members of the group, particularly, the emission line
galaxy No. 6 with a discordant redshift (Delta v = 2600 km/s). It is speculated
that the latter galaxy may be a infalling intruder to the group.Comment: accepted A&A, 7 pages, 6 figures are in separate file
Q_T Resummation in Transversely Polarized Drell-Yan Process
We calculate QCD corrections to transversely polarized Drell-Yan process at a
measured of the produced lepton pair in the dimensional regularization
scheme. The distribution is discussed resumming soft gluon effects
relevant for small .Comment: 4 pages, 1 figure, contribution to proceedings of International
Conference on QCD and Hadronic Physics, Beijing, June 16-20, 200
Unusually Large Fluctuations in the Statistics of Galaxy Formation at High Redshift
We show that various milestones of high-redshift galaxy formation, such as
the formation of the first stars or the complete reionization of the
intergalactic medium, occurred at different times in different regions of the
universe. The predicted spread in redshift, caused by large-scale fluctuations
in the number density of galaxies, is at least an order of magnitude larger
than previous expectations that argued for a sharp end to reionization. This
cosmic scatter in the abundance of galaxies introduces new features that affect
the nature of reionization and the expectations for future probes of
reionization, and may help explain the present properties of dwarf galaxies in
different environments. The predictions can be tested by future numerical
simulations and may be verified by upcoming observations. Current simulations,
limited to relatively small volumes and periodic boundary conditions, largely
omit cosmic scatter and its consequences. In particular, they artificially
produce a sudden end to reionization, and they underestimate the number of
galaxies by up to an order of magnitude at redshift 20.Comment: 8 ApJ pages, 4 figures, ApJ. Minor changes in revised version.
Originally first submitted for publication on Aug. 29, 200
Probing the Ionization State of the Universe at z>6
We present high signal-to-noise ratio Keck ESI spectra of the two quasars
known to have Gunn-Peterson absorption troughs, SDSS J1030+0524 (z=6.28) and
SDSS J1148+5251 (z=6.37). The Ly alpha and Ly beta troughs for SDSS J1030+0524
are very black and show no evidence for any emission over a redshift interval
of ~0.2 starting at z=6. On the other hand, SDSS J1148+5251 shows a number of
emission peaks in the Ly beta Gunn-Peterson trough along with a single weak
peak in the Ly alpha trough. The Ly alpha emission has corresponding Ly beta
emission, suggesting that it is indeed a region of lower optical depth in the
intergalactic medium at z=6.08.
The stronger Ly beta peaks in the spectrum of SDSS J1148+5251 could
conceivably also be the result of "leaks" in the IGM, but we suggest that they
are instead Ly alpha emission from an intervening galaxy at z=4.9. This
hypothesis gains credence from a strong complex of C IV absorption at the same
redshift and from the detection of continuum emission in the Ly alpha trough at
the expected brightness. If this proposal is correct, the quasar light has
probably been magnified through gravitational lensing by the intervening
galaxy. The Stromgren sphere observed in the absorption spectrum of SDSS
J1148+5251 is significantly smaller than expected based on its brightness,
which is consistent with the hypothesis that the quasar is lensed.
If our argument for lensing is correct, the optical depths derived from the
troughs of SDSS J1148+5251 are only lower limits (albeit still quite strong,
with tau(LyA)>16 inferred from the Ly beta trough.) The Ly beta absorption
trough of SDSS J1030+0524 gives the single best measurement of the IGM
transmission at z>6, with an inferred optical depth tau(LyA)>22.Comment: To appear in July 2003 AJ, 34 pages, 11 figures; minor changes/typos
fixe
Radio emission of Shakhbazian Compact Galaxy Groups
Three hundred fifty three radio sources from the NRAO VLA Sky Survey (NVSS)
(Condon et al. 1998) and the FIRST Survey (White et al. 1997}, are detected in
the areas of 179 Shakhbazian Compact Groups (ShCGs) of galaxies. Ninety three
of them are identified with galaxies in 74 ShCGs. Six radio sources have
complex structure. The radio spectra of 22 sources are determined. Radio
luminosities of galaxies in ShCGs are in general higher than that of galaxies
in Hickson Compact Groups (HCGs). The comparison of radio (at 1.4 GHz) and FIR
(at 60 m) fluxes of ShCG galaxies with that of HCG galaxies shows that
galaxies in ShCGs are relatively stronger emitters at radio wavelengths, while
galaxies in HCGs have relatively stronger FIR emission. The reasons of such
difference is discussed.Comment: 35 pages, 6 Postscript figures, ApJS in pres
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