1,396 research outputs found
Off-Shell Scattering Amplitudes for WW Scattering and the Role of the Photon Pole
We derive analytic expressions for high energy off-shell scattering
amplitudes of weak vector bosons. They are obtained from six fermion final
states in processes of the type . As an application we reconsider the
unitarity bounds on the Higgs mass. Particular attention is given to the role
of the photon exchange which has not been considered in earlier investigations;
we find that the photon weakens the bound of the Higgs mass.Comment: 16 pages, 8 figure
QCD Saturation Equations including Dipole-Dipole Correlation
We derive two coupled non-linear evolution equations corresponding to the
truncation of the Balitsky infinite hierarchy of saturation equations after
inclusion of dipole-dipole correlations, i.e. one step beyond the
Balitsky-Kovchegov (BK) equation. We exhibit an exact solution for maximal
correlation which still satisfies the same asymptotic geometric scaling as BK
but with the S-matrix going to 1/2 (instead of 0) in the full saturation
region.Comment: 4 pages, no figure. Comment, references and acknowledgment adde
Exact resolution of the Baxter equation for reggeized gluon interactions
The interaction of reggeized gluons in multi-colour QCD is considered in the
Baxter-Sklyanin representation, where the wave function is expressed as a
product of Baxter functions Q(lambda) and a pseudo-vacuum state. We find n
solutions of the Baxter equation for a composite state of n gluons with poles
of rank r in the upper lambda semi-plane and of rank n-1-r in the lower lambda
semi-plane (0 leq r leq n-1). These solutions are related by n-2 linear
equations with coefficients depending on coth (pi lambda). The poles cancel in
the wave function, bilinear combination of holomorphic and anti-holomorphic
Baxter functions, guaranteeing its normalizability. The quantization of the
intercepts of the corresponding Regge singularities appears as a result of the
physical requirements that the holomorphic energies for all solutions of the
Baxter equation are the same and the total energies, calculated around two
singularities lambda, lambda^* --> + i or -i, coincide. It results in simple
properties of the zeroes of the Baxter functions. For illustration we calculate
the parameters of the reggeon states constructed from three and four gluons.
For the Odderon the ground state has conformal spin |m -m | = 1 and its
intercept equals unity. The ground state of four reggeized gluons possesses
conformal spin 2 and its intercept turns out to be higher than that for the
BFKL Pomeron. We calculate the anomalous dimensions of the corresponding
operators for arbitrary alpha_s/omega.Comment: LaTex, 42 pages, 8 .ps figures. Expanded and improved versio
LHC soft physics and TMD gluon density at low x
We study the unintegrated, or transverse momentum dependent (TMD) gluon
distribution obtained from the best description of the LHC data on the
inclusive spectra of hadrons produced in the mid-rapidity region and low
transverse momenta at starting scale Q0^2 = 1 GeV^2. To extend this gluon
density at higher Q^2 we apply the Catani-Ciafoloni-Fiorani-Marchesini (CCFM)
evolution equation. The influence of the initial (starting) non-perturbative
gluon distribution is studied. The application of the obtained gluon density to
the analysis of the ep deep inelastic scattering allows us to get the results
which describe reasonably well the H1 and ZEUS data on the longitudinal proton
structure function FL(x,Q^2). So, the connection between the soft processes at
LHC and small x physics at HERA has been confirmed and extended to a wide
kinematical region.Comment: 8 pages, 3 figures, 1 tabl
A semiclassical realization of infrared renormalons
Perturbation series in quantum field theory are generally divergent
asymptotic series which are also typically not Borel resummable in the sense
that the resummed series is ambiguous. The ambiguity is associated with
singularities in the Borel plane on the positive real axis. In quantum
mechanics there are cases in which the ambiguity that arises in perturbation
theory cancels against a similarly ambiguous contribution from
instanton--anti-instanton events. In asymptotically free gauge theories this
mechanism does not suffice because perturbation theory develops ambiguities
associated with singularities in the Borel plane which are closer to the origin
by a factor of about N (the rank of the gauge group) compared to the
singularities realized by instanton events. These are called IR renormalon
poles, and on R**4 they do not possess any known semiclassical realization. By
using continuity on R**3 x S**1, and by generalizing the works of Bogomolny and
Zinn-Justin to QFT, we identify saddle point field configurations, e.g.,
bion--anti-bion events, corresponding to singularities in the Borel plane which
are of order N times closer to the origin than the 4d BPST
instanton--anti-instanton singularity. We conjecture that these are the leading
singularities in the Borel plane and that they are the incarnation of the
elusive renormalons in the weak coupling regime.Comment: 4 page
NLO Corrections to the kernel of the BKP-equations
We present results for the NLO kernel of the BKP equations for composite
states of three reggeized gluons in the Odderon channel, both in QCD and in N=4
SYM. The NLO kernel consists of the NLO BFKL kernel in the color octet
representation and the connected kernel, computed in the tree
approximation.Comment: 28 pages, 7 figure
Exclusive vector meson production at HERA from QCD with saturation
Following recent predictions that the geometric scaling properties of deep
inelastic scattering data in inclusive gamma*-p collisions are expected also in
exclusive diffractive processes, we investigate the diffractive production of
vector mesons. Using analytic results in the framework of the BK equation at
non-zero momentum transfer, we extend to the non-forward amplitude a
QCD-inspired forward saturation model including charm, following the
theoretical predictions for the momentum transfer dependence of the saturation
scale. We obtain a good fit to the available HERA data and make predictions for
deeply virtual Compton scattering measurements.Comment: 10 pages, 5 figures, full analysis including the charm contribution
and J/PSI production. Conclusions confirme
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