1,470 research outputs found
Elements of the theory of molecular spectra
The basic aspects of the theory concerning the spectra of multiatomic molecules are presented. The classification of the forms of motions in a molecule, the methods for determining the corresponding Schroudinger levels, the spectral types and the selection rules are discussed in order to identify their presence and state in outer space
Nuclear shadowing in inclusive and tagged deuteron structure functions and extraction of F_2^p-F_2^n at small x from electron-deuteron collider data
We review predictions of the theory of leading twist nuclear shadowing for
inclusive unpolarized and polarized deuteron structure functions F_2^D, g_1^D
and b_1^D and for the tagged deuteron structure function F_2^D(x,Q^2,\vec{p}).
We analyze the possibility to extract the neutron structure function F_2^n from
electron-deuteron data and demonstrate that an account of leading twist nuclear
shadowing leads to large corrections for the extraction of F_2^n from the
future deuteron collider data both in the inclusive and in the tagged structure
function modes. We suggest several strategies to address the extraction of
F_2^n and to measure at the same time the effect of nuclear shadowing via the
measurement of the distortion of the proton spectator spectrum in the
semi-inclusive e D \to e^{\prime}NX process. We address the issue of the final
state interactions in the e D \to e^{\prime}NX process and examine how they
affect the extraction of F_2^n.Comment: 19 pages, 7 figures. Published in Mod. Phys. Lett.
Asymptotic behavior of double parton distribution functions
The double parton distribution functions are investigated in the region of
small longitudinal momentum fractions in the leading logarithm approximation of
perturbative QCD. It is shown that these functions have the factorization
property in the case of one slow and one fast parton.Comment: 7 pages, revtex
Active-to-absorbing state phase transition in the presence of fluctuating environments: Weak and strong dynamic scaling
We investigate the scaling properties of phase transitions between survival
and extinction (active-to-absorbing state phase transition, AAPT) in a model,
that by itself belongs to the directed percolation (DP) universality class,
interacting with a spatio-temporally fluctuating environment having its own
non-trivial dynamics. We model the environment by (i) a randomly stirred fluid,
governed by the Navier-Stokes (NS) equation, and (ii) a fluctuating surface,
described either by the Kardar-Parisi-Zhang (KPZ) or the Edward-Wilkinson (EW)
equations. We show, by using a one-loop perturbative field theoretic set up,
that depending upon the spatial scaling of the variance of the external forces
that drive the environment (i.e., the NS, KPZ or EW equations), the system may
show {\em weak} or {\em strong dynamic scaling} at the critical point of active
to absorbing state phase transitions. In the former case AAPT displays scaling
belonging to the DP universality class, whereas in the latter case the
universal behavior is different.Comment: 17 pages, 2 figures, accepted in PR
Double parton scattering in double logarithm approximation of perturbative QCD
Using the explicit form of the known single distribution functions (the
Green's functions) in the double logarithm approximation of perturbative QCD,
we analyze the structure of splitting diagrams as a source of double parton
perturbative correlations in the proton. The related phenomenological effects
are discussed for the conditions of the LHC experiments.Comment: 8 pages, 1 figure, Refs. and explanations added, published version
(Phys. Rev. D
A fresh look at double parton scattering
A revised formula for the inclusive cross section for double parton
scattering in terms of the modified collinear two-parton distributions
extracted from deep inelastic scattering is suggested. The possible
phenomenological issues are discussed.Comment: 6 pages, 2 figures, revtex4, discussion slightly modified, 3
references adde
Increase with energy of parton transverse momenta in the fragmentation region in DIS and related phenomena
The dipole and the DGLAP approximations are combined with the
factorization theorem to demonstrate the fundamental property of pQCD: smaller
is the size of the colorless quark-gluon configurations in the fragmentation
region, more rapid is the increase of its interaction with the target as a
function of energy. First, we show that the transverse momenta of the
quark(antiquark) within the pair, produced in the fragmentation
region by the strongly virtual photon, increase with the decrease of x for
fixed . As practical consequence of these effects we show that the cross
sections of DIS and DVCS. We predict that the ratio of DVCS to DIS amplitudes
should very slowly approach one from above at very large collision energies.
Second, we study a closely related phenomenon of the increase of the transverse
momenta with the energy of the characteristic transverse momenta of the
gluon/quark configurations responsible for the transition to the black disk
regime. We discuss the impact of this phenomenona on the slowing of the
dependence on the initial energy of the coherence length. We demonstrate that a
rapid projectile has the biconcave shape, which is different from the
expectations of the preQCD parton model where a fast hadron has a pancake
shape. We show that the increase of the transverse momenta leads to a new
expression for the total cross section of a DIS scattering at very large
energies, relevant to LHeC and LHC. We discuss the impact of the discovered
phenomena on the hard processes in pp collisions, and on the dominance
ofdifferent phases of chiral and conformal symmetries in the central and
peripheral pp, pA, and AA collisions.Comment: 37 pages, 6 figures, uses file pdfsync.sty some typos and
misspellings are eliminate
Prompt neutrino fluxes from atmospheric charm
We calculate the prompt neutrino flux from atmospheric charm production by
cosmic rays, using the dipole picture in a perturbative QCD framework, which
incorporates the parton saturation effects present at high energies. We compare
our results with the next-to-leading order perturbative QCD result and find
that saturation effects are large for neutrino energies above 10^6 GeV, leading
to a substantial suppression of the prompt neutrino flux. We comment on the
range of prompt neutrino fluxes due to theoretical uncertainties.Comment: 13 pages with 11 figures; expanded discussion, added references,
version to be published in Phys. Rev.
Scenario for Ultrarelativistic Nuclear Collisions: Space--Time Picture of Quantum Fluctuations and the Birth of QGP
We study the dynamics of quantum fluctuations which take place at the
earliest stage of high-energy processes and the conditions under which the data
from e-p deep-inelastic scattering may serve as an input for computing the
initial data for heavy-ion collisions at high energies. Our method is
essentially based on the space-time picture of these seemingly different
phenomena. We prove that the ultra-violet renormalization of the virtual loops
does not bring any scale into the problem. The scale appears only in connection
with the collinear cut-off in the evolution equations and is defined by the
physical properties of the final state. In heavy-ion collisions the basic
screening effect is due to the mass of the collective modes (plasmons) in the
dense non-equilibrium quark-gluon system, which is estimated. We avoid the
standard parton phenomenology and suggest a dedicated class of evolution
equations which describe the dynamics of quantum fluctuations in heavy-ion
collisions.Comment: 54 pages, 11 Postscript figures, uses RevTe
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