46 research outputs found
Interference between initial and final state radiation in a QCD medium
We investigate the color coherence pattern between initial and final state
radiation in the presence of a QCD medium. We derive the medium-induced gluon
spectrum of an "asymptotic" parton which suffers a hard scattering and
subsequently crosses the medium. The angular distribution of the induced gluon
spectrum is modified when one includes interference terms between the incoming
and the outgoing parton at finite angle between them. The coherent, incoherent
and soft limits of the medium-induced gluon spectrum are studied. In the soft
limit, we provide a simple and intuitive probabilistic picture which could be
of interest for Monte Carlo implementations. The configuration studied here may
have phenomenological consequences in high energy nuclear collisions.Comment: 9 pages, 2 figures. Typos corrected and added remarks. Accepted for
publication in Phys. Lett.
Rectangular Wilson Loops at Large N
This work is about pure Yang-Mills theory in four Euclidean dimensions with
gauge group SU(N). We study rectangular smeared Wilson loops on the lattice at
large N and relatively close to the large-N transition point in their
eigenvalue density. We show that the string tension can be extracted from these
loops but their dependence on shape differs from the asymptotic prediction of
effective string theory.Comment: 47 pages, 21 figures, 8 table
Quarkonium Photoproduction at Next-to-leading Order
We present the calculation of O(as^2 aem) corrections to heavy-quarkonium
total photoproduction cross-sections. Results are given for the colour-octet
component of S and P waves. The calculation is performed using covariant
projectors in dimensional regularization. A phenomenological study of the
results, including a discussion of the high-energy behaviour of the cross
sections, is presented. For gamma-p energies up to few hundred GeV the NLO
corrections significantly reduce the scale dependence of the production rates
relative to the Born-level results. Large small-x corrections arise at higher
energies, making the predictions strongly dependent on the shape of the gluon
density and on the choice of factorization scale.Comment: 32 pages, Latex, epsfig, 13 figure
Central Exclusive Production in QCD
We investigate the theoretical description of the central exclusive
production process, h1+h2 -> h1+X+h2. Taking Higgs production as an example, we
sum logarithmically enhanced corrections appearing in the perturbation series
to all orders in the strong coupling. Our results agree with those originally
presented by Khoze, Martin and Ryskin except that the scale appearing in the
Sudakov factor, mu=0.62 \sqrt{\hat{s}}, should be replaced with
mu=\sqrt{\hat{s}}, where \sqrt{\hat{s}} is the invariant mass of the centrally
produced system. We confirm this result using a fixed-order calculation and
show that the replacement leads to approximately a factor 2 suppression in the
cross-section for central system masses in the range 100-500 GeV.Comment: 41 pages, 19 figures; minor typos fixed; version published in JHE
Correlation function of null polygonal Wilson loops with local operators
We consider the correlator of a light-like polygonal Wilson loop
with n cusps with a local operator (like the dilaton or the chiral primary
scalar) in planar N =4 super Yang-Mills theory. As a consequence of conformal
symmetry, the main part of such correlator is a function F of 3n-11 conformal
ratios. The first non-trivial case is n=4 when F depends on just one conformal
ratio \zeta. This makes the corresponding correlator one of the simplest
non-trivial observables that one would like to compute for generic values of
the `t Hooft coupling \lambda. We compute F(\zeta,\lambda) at leading order in
both the strong coupling regime (using semiclassical AdS5 x S5 string theory)
and the weak coupling regime (using perturbative gauge theory). Some results
are also obtained for polygonal Wilson loops with more than four edges.
Furthermore, we also discuss a connection to the relation between a correlator
of local operators at null-separated positions and cusped Wilson loop suggested
in arXiv:1007.3243.Comment: 36 pages, 2 figure
J/psi Production at LEP: Revisited and Resummed
We present the leading order differential and total rates for J/\psi
production at LEP. By leading order we mean all terms of the form
alpha_s[alpha_s log(M_Z^2/M_{psi}^2)]^n and alpha_s^{n+1} log^l(z^2)
log^m(M_Z^2/M_{psi}^2), (l+m=2n-1), in the regions z=2E_psi/M_Z ~ O(1) and z <<
1, respectively. In the intermediate region we interpolate using the available
data. This resummation eliminates the O[alpha_s(M_psi)/alpha_s(M_Z)]~ 2
theoretical uncertainties in previous calculations. The log(z) resummation
results in a suppression of the small z region due to coherent gluon emission.
Comparing the zeroth moment with the LEP data we find the value for the
effective octet matrix element to be =0.019 GeV^3. The
theoretical uncertainties are substantially smaller than those from Tevatron
extractions. Using this value of the octet matrix element we make a prediction
for the first moment of the differential rate and find that the resummed
differential decay rate is in much better agreement with preliminary data than
the color singlet result or the unresummed color octet prediction.Comment: LATEX, 17 pages, 3 figures included. References to ALEPH
collaboration change
NLO Production and Decay of Quarkonium
We present a calculation of next-to-leading-order (NLO) QCD corrections to
total hadronic production cross sections and to light-hadron-decay rates of
heavy quarkonium states. Both colour-singlet and colour-octet contributions are
included. We discuss in detail the use of covariant projectors in dimensional
regularization, the structure of soft-gluon emission and the overall finiteness
of radiative corrections. We compare our approach with the
NLO version of the threshold-expansion technique recently introduced by
Braaten and Chen. Most of the results presented here are new. Others
represent the first independent reevaluation of calculations already known in
the literature. In this case a comparison with previous findings is reported.Comment: 65 pages, Latex, epsfig, 8 figures. Typos corrected and improvements
made to the text. Version to appear on Nucl Phys.
Serum nucleosomes during neoadjuvant chemotherapy in patients with cervical cancer. Predictive and prognostic significance
BACKGROUND: It has been shown that free DNA circulates in serum plasma of patients with cancer and that at least part is present in the form of oligo- and monucleosomes, a marker of cell death. Preliminary data has shown a good correlation between decrease of nucleosomes with response and prognosis. Here, we performed pre- and post-chemotherapy determinations of serum nucleosomes with an enzyme-linked immunosorbent assay (ELISA) method in a group of patients with cervical cancer receiving neoadjuvant chemotherapy. METHODS: From December 2000 to June 2001, 41 patients with cervical cancer staged as FIGO stages IB2-IIIB received three 21-day courses of carboplatin and paclitaxel, both administered at day 1; then, patients underwent radical hysterectomy. Nucleosomes were measured the day before (baseline), at day seven of the first course and day seven of the third course of chemotherapy. Values of nucleosomes were analyzed with regard to pathologic response and to time to progression-free and overall survival. RESULTS: All patients completed chemotherapy, were evaluable for pathologic response, and had nucleosome levels determined. At a mean follow-up of 23 months (range, 7–26 months), projected progression time and overall survival were 80.3 and 80.4%, respectively. Mean differential values of nucleosomes were lower in the third course as compared with the first course (p >0.001). The decrease in the third course correlated with pathologic response (p = 0.041). Survival analysis showed a statistically significant, better progression-free and survival time in patients who showed lower levels at the third course (p = 0.0243 and p = 0.0260, respectively). Cox regression analysis demonstrated that nucleosome increase in the third course increased risk of death to 6.86 (95% confidence interval [CI 95%], 0.84–56.0). CONCLUSION: Serum nucleosomes may have a predictive role for response and prognostic significance in patients with cervical cancer patients treated with neoadjuvant chemotherapy
Resummation of small-x double logarithms in QCD: semi-inclusive electron-positron annihilation
We have derived the coefficients of the highest three 1/x-enhanced small-x
logarithms of all timelike splitting functions and the coefficient functions
for the transverse fragmentation function in one-particle inclusive e^+e^-
annihilation at (in principle) all orders in massless perturbative QCD. For the
longitudinal fragmentation function we present the respective two highest
contributions. These results have been obtained from KLN-related decompositions
of the unfactorized fragmentation functions in dimensional regularization and
their structure imposed by the mass-factorization theorem. The resummation is
found to completely remove the huge small-x spikes present in the fixed-order
results for all quantities above, allowing for stable results down to very
small values of the momentum fraction and scaling variable x. Our calculations
can be extended to (at least) the corresponding as^n ln^(2n-l) x contributions
to the above quantities and their counterparts in deep-inelastic scattering.Comment: 27 pages, LaTeX, 6 eps-figure
Scaling laws for density correlations and fluctuations in multiparticle dynamics
Experimental data are presented on particle correlations and fluctuations in
various high-energy multiparticle collisions, with special emphasis on evidence
for scaling-law evolution in small phase-space domains. The notions of
intermittency and fractality as related to the above findings are described.
Phenomenological and theoretical work on the subject is reviewed.Comment: 139 pages, LATEX, 67 figures (hard copies on request from
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