800 research outputs found
Positivity bounds on gluon TMDs for hadrons of spin 1
We consider the transverse momentum dependent gluon distribution functions
(called gluon TMDs) by studying the light-front gluon-gluon correlator,
extending the results for unpolarized and vector polarized targets to also
include tensor polarized targets -- the latter type of polarization is relevant
for targets of spin . The light-front correlator includes
process-dependent gauge links to guarantee color gauge invariance. As from the
experimental side the gluon TMDs are largely unknown, we present positivity
bounds for combinations of leading-twist gluon distributions that may be used
to estimate their maximal contribution to observables. Since the gluonic
content of hadrons is particularly relevant in the small- kinematic region,
we also study these bounds in the small- limit for the dipole-type gauge
link structure using matrix elements of a single Wilson loop.Comment: 10 page
Renormalization group invariants in supersymmetric theories: one- and two-loop results
We stress the potential usefulness of renormalization group invariants.
Especially particular combinations thereof could for instance be used as probes
into patterns of supersymmetry breaking in the MSSM at inaccessibly high
energies. We search for these renormalization group invariants in two
systematic ways: on the one hand by making use of symmetry arguments and on the
other by means of a completely automated exhaustive search through a large
class of candidate invariants. At the one-loop level, we find all known
invariants for the MSSM and in fact several more, and extend our results to the
more constrained pMSSM and dMSSM, leading to even more invariants. Extending
our search to the two-loop level we find that the number of invariants is
considerably reduced
Directed flow from C-odd gluon correlations at small
It is shown that odd harmonic azimuthal correlations, including the directed
flow , in forward two-particle production in peripheral proton-nucleus
() collisions can arise simply from the radial nuclear profile of a large
nucleus. This requires consideration of the C-odd part of the gluonic
generalized transverse momentum dependent (GTMD) correlator of nucleons in the
nucleus. The gluonic GTMD correlator is the Fourier transform of an off-forward
hadronic matrix element containing gluonic field strength tensors that are
connected by gauge links. It is parametrized in terms of various gluon GTMD
distribution functions (GTMDs). We show (in a gauge invariant way) that for the
relevant dipole-type gauge link structure in the small- limit the GTMD
correlator reduces to a generalized Wilson loop correlator. The Wilson loop
correlator is parametrized in terms of a single function, implying that in the
region of small there is only one independent dipole-type GTMD, which can
have a C-odd part. We show that the odderon Wigner distribution, which is
related to this C-odd dipole GTMD by a Fourier transform, generates odd
harmonics in the two-particle azimuthal correlations in peripheral
collisions. We calculate the first odd harmonic for forward production
within the color glass condensate framework in the limit of a large number of
colors. We find that nonzero odd harmonics are present without breaking the
rotational symmetry of the nucleus, arising just from its inhomogeneity in the
radial direction. Using a CGC model with a cubic action, we illustrate that
percent level can arise from this C-odd mechanism. In contrast, we show
that only even harmonics arise in diffractive dijet production in
ultra-peripheral collisions where this gluon dipole GTMD also appears.Comment: 23 pages, 3 figures. v2: References added; Added plot for A=63 in
Fig.3 and a discussion on the A dependence. Version accepted for publication
in JHE
Theoretical restrictions on the parameters of the indirect addilog system revisited
The correct parameter restrictions- less restrictive than commonly thought-of the indirect addilog system (IAS) are derived. Under correct restrictions, the IAS is superior to the linear expenditure system in computable general equilibrium models with data scarcity.CGE-modelling;indirect addilog system;parameter restriction
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