2,126 research outputs found
Fully double-logarithm-resummed cross sections
We calculate the complete double logarithmic contribution to cross sections
for semi-inclusive hadron production in the modified minimal-subtraction scheme
by applying dimensional regularization to the double logarithm approximation.
The full double logarithmic contribution to the coefficient functions for
inclusive hadron production in electron-positron annihilation is obtained in
this scheme for the first time. Our result agrees with all fixed order results
in the literature, which extend to next-next-to-leading order.Comment: To appear in Nuclear Physics
Screening of pair fluctuations in superconductors with coupled shallow and deep bands: a route to higher temperature superconductivity
A combination of strong Cooper pairing and weak superconducting fluctuations
is crucial to achieve and stabilize high-Tc superconductivity. We demonstrate
that a coexistence of a shallow carrier band with strong pairing and a deep
band with weak pairing, together with the Josephson-like pair transfer between
the bands to couple the two condensates, realizes an optimal multicomponent
superconductivity regime: it preserves strong pairing to generate large gaps
and a very high critical temperature but screens the detrimental
superconducting fluctuations, thereby suppressing the pseudogap state.
Surprisingly, we find that the screening is very efficient even when the
inter-band coupling is very small. Thus, a multi-band superconductor with a
coherent mixture of condensates in the BCS regime (deep band) and in the
BCS-BEC crossover regime (shallow band) offers a promising route to higher
critical temperatures.Comment: 8 pages, 1 figure, including supplemental material
Unifying the Fixed Order Evolution of Fragmentation Functions with the Modified Leading Logarithm Approximation
An approach which unifies the Double Logarithmic Approximation at small x and
the leading order DGLAP evolution of fragmentation functions at large x is
presented. This approach reproduces exactly the Modified Leading Logarithm
Approximation, but is more complete due to the degrees of freedom given to the
quark sector and the inclusion of the fixed order terms. We find that data from
the largest x values to the peak region can be better fitted than with other
approaches
Factorization breaking in high-transverse-momentum charged-hadron production at the Tevatron?
We compare the transverse momentum (p_T) distribution of inclusive
light-charged-particle production measured by the CDF Collaboration at the
Fermilab Tevatron with the theoretical prediction evaluated at next-to-leading
order in quantum chromodynamics (QCD) using fragmentation functions recently
determined through a global data fit. While, in the lower p_T range, the data
agree with the prediction within the theoretical error or slightly undershoot
it, they significantly exceed it in the upper p_T range, by several orders of
magnitude at the largest values of p_T, where perturbation theory should be
most reliable. This disagreement is too large to be remedied by introducing
additional produced particles into the calculation, and potentially challenges
the validity of the factorization theorem on which the parton model of QCD
relies. Clearly, a breakdown of the factorization theorem, being a fundamental
property of QCD, would be extremely difficult to understand.Comment: 9 pages, 5 figures; discussion extended, references added; accepted
for publication in Physical Review Letter
Transverse Takahashi Identities and Their Implications for Gauge Independent Dynamical Chiral Symmetry Breaking
In this article, we employ transverse Takahashi identities to impose valuable
non-perturbative constraints on the transverse part of the fermion-photon
vertex in terms of new form factors, the so called functions. We show
that the implementation of these identities is crucial in ensuring the correct
local gauge transformation of the fermion propagator and its multiplicative
renormalizability. Our construction incorporates the correct symmetry
properties of the under charge conjugation operation as well as their
well-known one-loop expansion in the asymptotic configuration of incoming and
outgoing momenta. Furthermore, we make an explicit analysis of various existing
constructions of this vertex against the demands of transverse Takahashi
identities and the previously established key features of quantum
electrodynamics, such as gauge invariance of the critical coupling above which
chiral symmetry is dynamically broken. We construct a simple example in its
quenched version and compute the mass function as we vary the coupling strength
and also calculate the corresponding anomalous dimensions . There is
an excellent fit to the Miransky scalling law and we find rather
naturally in accordance with some earlier results in literature, using
arguments based on Cornwall-Jackiw-Tomboulis effective potential technique.
Moreover, we numerically confirm the gauge invariance of this critical
coupling.Comment: 16 pages, 4 figure
Low x particle spectra in the Modified Leading Logarithm Approximation
We show that the higher moments of the evolution obtained from the Modified
Leading Logarithm Approximation may be regarded as spurious higher order terms
in perturbation theory, and that neglecting them leads to a good description of
the data around and above the peak in . Furthermore, we use this
study of the moments to show that at high energy the Limiting Spectrum with
Local Parton-Hadron Duality may also be derived from the Modified Leading
Logarithm Approximation without any non-perturbative assumptions.Comment: Submitted to Eur. Phys. J.,
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