5,295 research outputs found
New theory of the gamma-alpha phase transition in Ce: quadrupolar ordering
We present a theoretical model of the "isostructural" \gamma-\alpha phase
transition in Ce which is based on quadrupolar interactions due to coupled
charge density fluctuations of 4f electrons and of conduction electrons.
Conduction electrons are treated in tight-binding approximation. The
\gamma-\alpha transition is described as an orientational ordering of
quadrupolar electronic densities in a Pa3 structure. The quadrupolar order of
the conduction electron densities is complementary to the quadrupolar order of
4f electron densities. The inclusion of conduction electrons leads to an
increase of the lattice contraction at the \gamma-\alpha transition in
comparison to the sole effect of 4f electrons. We calculate the Bragg
scattering law and suggest synchrotron radiation experiments in order to check
the Pa3 structure. The theory is capable of accounting for transitions to
phases of non-cubic symmetry, but it is not sufficient to describe the magnetic
phenomena which we ascribe to the Kondo mechanism. We also present a
microscopic derivation of multipolar interactions and discuss the crystal field
of \gamma-Ce.Comment: 19 pages, 4 figures, full version to be published in Eur. Phys. J.
Production of two pairs in gluon-gluon scattering in high energy proton-proton collisions
We calculate cross sections for in the
high-energy approximation in the mixed (longitudinal momentum fraction, impact
parameter) and momentum space representations. Besides the total cross section
as a function of subsystem energy also differential distributions (in quark
rapidity, transverse momentum, , invariant mass) are presented.
The elementary cross section is used to calculate production of in single-parton scattering (SPS) in proton-proton collisions. We
present integrated cross section as a function of proton-proton center of mass
energy as well as differential distribution in . The
results are compared with corresponding results for double-parton scattering
(DPS) discussed recently in the literature. We find that the considered SPS
contribution to production is at high energy ( 5 TeV) much smaller than that for DPS contribution.Comment: 17 pages, 11 figure
Breaking of k_\perp-factorization for Single Jet Production off Nuclei
The linear k_\perp-factorization is part and parcel of the pQCD description
of high energy hard processes off free nucleons.
In the case of heavy nuclear targets the very concept of nuclear parton
density becomes ill-defined as exemplified by the recent derivation [2] of
nonlinear nuclear k_\perp-factorization for forward dijet production in DIS off
nuclei. Here we report a derivation of the related breaking of
k_\perp-factorization for single-jet processes. We present a general formalism
and apply it to several cases of practical interest: open charm and quark and
gluon jet production in the central to beam fragmentation region of
\gamma^*p,\gamma^*A, pp and pA collisions. We show how the pattern of
k_\perp-factorization breaking and the nature and number of exchanged nuclear
pomerons do change within the phase space of produced quark and gluon jets. As
an application of the nonlinear k_\perp-factorization we discuss the Cronin
effect. Our results are also applicable to the p_\perp-dependence of the
Landau-Pomeranchuk-Migdal effect for, and nuclear quenching of, jets produced
in the proton hemisphere of pA collisions.Comment: 55 pages, 9 eps figures, presentation shortened, a number of typos
removed, to appear in Phys. Rev.
Evolution of high-mass diffraction from the light quark valence component of the pomeron
We analyze the contribution from excitation of the Fock states of the photon to high mass diffraction in
DIS. We show that the large behavior of this contribution can be
described by the DLLA evolution from the non-perturbative valence
state of the pomeron. Although of higher order in pQCD, the new contribution to
high-mass diffraction is comparable to that from the excitation of the Fock state of the photon.Comment: 12 pages, 2 figures, the oublished version. The slight numerical
errors corrected, all conclusions are retaine
Kinetic Scalar Curvature Extended Gravity
In this work we study a modified version of vacuum gravity with a
kinetic term which consists of the first derivatives of the Ricci scalar. We
develop the general formalism of this kinetic Ricci modified gravity and
we emphasize on cosmological applications for a spatially flat cosmological
background. By using the formalism of this theory, we investigate how it is
possible to realize various cosmological scenarios. Also we demonstrate that
this theoretical framework can be treated as a reconstruction method, in the
context of which it is possible to realize various exotic cosmologies for
ordinary Einstein-Hilbert action. Finally, we derive the scalar-tensor
counterpart theory of this kinetic Ricci modified gravity, and we show
the mathematical equivalence of the two theories.Comment: NPB Accepte
Crystal Structures of Polymerized Fullerides AC60, A=K, Rb, Cs and Alkali-mediated Interactions
Starting from a model of rigid interacting C60 polymer chains on an
orthorhombic lattice, we study the mutual orientation of the chains and the
stability of the crystalline structures Pmnn and I2/m. We take into account i)
van der Waals interactions and electric quadrupole interactions between C60
monomers on different chains as well as ii) interactions of the monomers with
the surrounding alkali atoms. The direct interactions i) always lead to an
antiferrorotational structure Pmnn with alternate orientation of the C60 chains
in planes (001). The interactions ii) with the alkalis consist of two parts:
translation-rotation (TR) coupling where the orientations of the chains
interact with displacements of the alkalis, and quadrupolar electronic
polarizability (ep) coupling, where the electric quadrupoles on the C60
monomers interact with induced quadrupoles due to excited electronic d states
of the alkalis. Both interactions ii) lead to an effective
orientation-orientation interaction between the C60 chains and always favor the
ferrorotational structure I2/m where C60 chains have a same orientation. The
structures Pmnn for KC60 and I2/m for Rb- and CsC60 are the result of a
competition between the direct interaction i) and the alkali-mediated
interactions ii). In Rb- and CsC60 the latter are found to be dominant, the
preponderant role being played by the quadrupolar electronic polarizability of
the alkali ions.Comment: J.Chem.Phys., in press, 14 pages, 3 figures, 8 table
Quenching of Leading Jets and Particles: the p_t Dependent Landau-Pomeranchuk-Migdal effect from Nonlinear k_t Factorization
We report the first derivation of the Landau-Pomeranchuk-Migdal effect for
leading jets at fixed values of the transverse momentum p_t in the beam
fragmentation region of hadron-nucleus collisions from RHIC (Relativistic Heavy
Ion Collider) to LHC (Large Hadron Collider). The major novelty of this work is
a derivation of the missing virtual radiative pQCD correction to these
processes - the real-emission radiative corrections are already available in
the literature. We manifestly implement the unitarity relation, which in the
simplest form requires that upon summing over the virtual and real-emission
corrections the total number of scattered quarks must exactly equal unity. For
the free-nucleon target, the leading jet spectrum is shown to satisfy the
familiar linear Balitsky-Fadin-Kuraev-Lipatov leading log(1/x) (LL-1/x)
evolution. For nuclear targets, the nonlinear k_t-factorization for the LL-1/x
evolution of the leading jet sepctrum is shown to exactly match the equally
nonlinear LL-1/x evolution of the collective nuclear glue - there emerges a
unique linear k_t-factorization relation between the two nonlinear evolving
nuclear observables. We argue that within the standard dilute uncorrelated
nucleonic gas treatment of heavy nuclei, in the finite energy range from RHIC
to LHC, the leading jet spectrum can be evolved in the LL-1/x
Balitsky-Kovchegov approximation. We comment on the extension of these results
to, and their possible reggeon field theory interpretation for, mid-rapidity
jets at LHC.Comment: 36 pages, 8 eps figs, revised, discussion on reggeon interpretation
and refs. adde
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