13 research outputs found
Low-x evolution of parton densities
It is shown that a Bessel-like behaviour of the structure function F2 at
small x, obtained for a flat initial condition in the DGLAP evolution
equations, leads to good agreement with the deep inelastic scattering
experimental data from HERA.Comment: 8 pages, 3 figures, in Proc. of the third International Workshop on
Multiple Partonic Interactions at the LHC (21-25 November 2011, DESY,
Hamburg
Ultrahigh-energy neutrino-nucleon deep-inelastic scattering and the Froissart bound
We present a simple formula for the total cross section sigma^{nu N} of
neutral- and charged-current deep-inelastic scattering of ultrahigh-energy
neutrinos on isoscalar nuclear targets, which is proportional to the structure
function F_2^{nu N}(M_V^2/s, M_V^2), where M_V is the intermediate-boson mass
and s is the square of the center-of-mass energy. The coefficient in the front
of F_2^{nu N}(x, Q^2) depends on the asymptotic low-x behavior of F_2^{nu N}.
It contains an additional ln(s) term if F_2^{nu N} scales with a power of
ln(1/x). Hence, an asymptotic low-x behavior F_2^{nu N} propto ln^2(1/x), which
is frequently assumed in the literature, already leads to a violation of the
Froissart bound on sigma^{nu N}.Comment: 5 pages, 2 figures, to appear in Physical Review Letter
Recent progress on the accurate determination of the equation of state of neutron and nuclear matter
The problem of accurately determining the equation of state of nuclear and
neutron matter at density near and beyond saturation is still an open
challenge. In this paper we will review the most recent progress made by means
of Quantum Monte Carlo calculations, which are at present the only ab-inito
method capable to treat a sufficiently large number of particles to give
meaningful estimates depending only on the choice of the nucleon-nucleon
interaction. In particular, we will discuss the introduction of
density-dependent interactions, the study of the temperature dependence of the
equation of state, and the possibility of accurately studying the effect of the
onset of hyperons by developing an accurate hyperon-nucleon and
hyperon-nucleon-nucleon interaction.Comment: 3 figures, 1 table, to appear in the Proceedings of "XIII Convegno di
Cortona su Problemi di Fisica Nucleare Teorica", Cortona (Italy), April 6-8,
201
S-pairing in neutron matter. I. Correlated Basis Function Theory
S-wave pairing in neutron matter is studied within an extension of correlated
basis function (CBF) theory to include the strong, short range spatial
correlations due to realistic nuclear forces and the pairing correlations of
the Bardeen, Cooper and Schrieffer (BCS) approach. The correlation operator
contains central as well as tensor components. The correlated BCS scheme of
Ref. [Nucl. Phys. A363 (1981) 383], developed for simple scalar correlations,
is generalized to this more realistic case. The energy of the correlated pair
condensed phase of neutron matter is evaluated at the two--body order of the
cluster expansion, but considering the one--body density and the corresponding
energy vertex corrections at the first order of the Power Series expansion.
Based on these approximations, we have derived a system of Euler equations for
the correlation factors and for the BCS amplitudes, resulting in correlated non
linear gap equations, formally close to the standard BCS ones. These equations
have been solved for the momentum independent part of several realistic
potentials (Reid, Argonne v_{14} and Argonne v_{8'}) to stress the role of the
tensor correlations and of the many--body effects. Simple Jastrow correlations
and/or the lack of the density corrections enhance the gap with respect to
uncorrelated BCS, whereas it is reduced according to the strength of the tensor
interaction and following the inclusion of many--body contributions.Comment: 20 pages, 8 figures, 1 tabl
Small-x behavior of the structure function F_2 and its slope partial ln(F_2)/partial ln(1/x) for "frozen" and analytic strong-coupling constants
Using the leading-twist approximation of the Wilson operator product
expansion with "frozen" and analytic versions of the strong-coupling constant,
we show that the Bessel-inspired behavior of the structure function F_2 and its
slope\break partial ln(F_2)/partial ln(1/x) at small values of x, obtained for
a flat initial condition in the DGLAP evolution equations, leads to good
agreement with experimental data of deep-inelastic scattering at DESY HERA.Comment: new curves added to Figs. 1 and 2, minor changes to the text,
accepted for publication in Phys. Lett.
Heavy-quark contributions to the ratio F_L/F_2 at low x
We study the heavy-quark contribution to the proton structure functions
F_2^i(x,Q^2) and F_L^i(x,Q^2), with i=c,b, for small values of Bjorken's x
variable at next-to-lading order and provide compact formulas for their ratios
R_i=F_L^i/F_2^i that are useful to extract F_2^i(x,Q^2) from measurements of
the doubly differential cross section of inclusive deep-inelastic scattering at
DESY HERA. Our approach naturally explains why R_i is approximately independent
of x and the details of the parton distributions in the small-x regime.Comment: 11 pages, 1 figur