1,195 research outputs found
Non-linear power spectra of dark and luminous matter in halo model of structure formation
The late stages of large-scale structure evolution are treated
semi-analytically within the framework of modified halo model. We suggest
simple yet accurate approximation for relating the non-linear amplitude to
linear one for spherical density perturbation. For halo concentration
parameter, , a new computation technique is proposed, which eliminates the
need of interim evaluation of the . Validity of the technique is
proved for CDM and WDM cosmologies. Also, the parameters for
Sheth-Tormen mass function are estimated. The modified and extended halo model
is applied for determination of non-linear power spectrum of dark matter, as
well as for galaxy power spectrum estimation. The semi-analytical techniques
for dark matter power spectrum are verified by comparison with data from
numerical simulations. Also, the predictions for the galaxy power spectra are
confronted with 'observed' data from PSCz and SDSS galaxy catalogs, good
accordance is found.Comment: 18 pages, 8 figures; major changes from the previous version;
accepted for publivation in Phys. Rev.
Electronic spin working mechanically
A single-electron tunneling (SET) device with a nanoscale central island that
can move with respect to the bulk source- and drain electrodes allows for a
nanoelectromechanical (NEM) coupling between the electrical current through the
device and mechanical vibrations of the island. Although an electromechanical
"shuttle" instability and the associated phenomenon of single-electron
shuttling were predicted more than 15 years ago, both theoretical and
experimental studies of NEM-SET structures are still carried out. New
functionalities based on quantum coherence, Coulomb correlations and coherent
electron-spin dynamics are of particular current interest. In this article we
present a short review of recent activities in this area.Comment: 17 pages, 11 figures. arXiv admin note: substantial text overlap with
arXiv:1303.074
Charge and Spin Effects in Mesoscopic Josephson Junctions
We consider the charge and spin effects in low dimensional superconducting
weak links. The first part of the review deals with the effects of
electron-electron interaction in Superconductor/Luttinger liquid/Superconductor
junctions. The experimental realization of this mesoscopic hybrid system can be
the individual single wall carbon nanotube that bridges the gap between two
bulk superconductors. The dc Josephson current through a Luttinger liquid in
the limits of perfectly and poorly transmitting junctions is evaluated. The
relationship between the Josephson effect in a long SNS junction and the
Casimir effect is discussed. In the second part of the paper we review the
recent results concerning the influence of the Zeeman and Rashba interactions
on the thermodynamical properties of ballistic S/QW/S junction fabricated in
two dimensional electron gas. It is shown that in magnetically controlled
junction there are conditions for resonant Cooper pair transition which results
in giant supercurrent through a tunnel junction and a giant magnetic response
of a multichannel SNS junction. The supercurrent induced by the joint action of
the Zeeman and Rashba interactions in 1D quantum wires connected to bulk
superconductors is predicted.Comment: 36 pages, 8 figures; minor changes in reference
Scaling of Particle and Transverse Energy Production in 208Pb+208Pb collisions at 158 A GeV
Transverse energy, charged particle pseudorapidity distributions and photon
transverse momentum spectra have been studied as a function of the number of
participants (N_{part}) and the number of binary nucleon-nucleon collisions
(N_{coll}) in 158 A GeV Pb+Pb collisions over a wide impact parameter range. A
scaling of the transverse energy pseudorapidity density at midrapidity as
N_{part}^{1.08 \pm 0.06} and N_{coll}^{0.83 \pm 0.05} is observed. For the
charged particle pseudorapidity density at midrapidity we find a scaling as
N_{part}^{1.07 \pm 0.04} and N_{coll}^{0.82 \pm 0.03}. This faster than linear
scaling with N_{part} indicates a violation of the naive Wounded Nucleon Model.Comment: 13 pages, 16 figures, submitted to European Physical Journal C
(revised results for scaling exponents
Rapidity and k_T dependence of HBT correlations in Au+Au collisions at 200 GeV with PHOBOS
Two-particle correlations of identical charged pion pairs from Au+Au
collisions at sqrt(s_NN) = 200 GeV were measured by the PHOBOS experiment at
RHIC. Data for the most central (0--15%) events were analyzed with
Bertsch-Pratt (BP) and Yano-Koonin-Podgoretskii (YKP) parameterizations using
pairs with rapidities of 0.4 < y < 1.3 and transverse momenta 0.1 < k_T < 1.4
GeV/c. The Bertsch-Pratt radii decrease as a function of pair transverse
momentum. The pair rapidity Y_pipi roughly scales with the source rapidity
Y_YKP, indicating strong dynamical correlations.Comment: 5 pages, 2 figures. To appear in the proceedings of Seventeenth
International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions
(Quark Matter 2004), Oakland, California from January 11-17, 2004. Submitted
to Journal of Physics G: Nuclear and Particle Physic
Interferometry of Direct Photons in Central 280Pb+208Pb Collisions at 158A GeV
Two-particle correlations of direct photons were measured in central
208Pb+208Pb collisions at 158 AGeV. The invariant interferometric radii were
extracted for 100<K_T<300 MeV/c and compared to radii extracted from charged
pion correlations. The yield of soft direct photons, K_T<300 MeV/c, was
extracted from the correlation strength and compared to theoretical
calculations.Comment: 5 pages, 4 figure
Systematics of Inclusive Photon Production in 158 AGeV Pb Induced Reactions on Ni, Nb, and Pb Targets
The multiplicity of inclusive photons has been measured on an event-by-event
basis for 158 AGeV Pb induced reactions on Ni, Nb, and Pb targets. The
systematics of the pseudorapidity densities at midrapidity (rho_max) and the
width of the pseudorapidity distributions have been studied for varying
centralities for these collisions. A power law fit to the photon yield as a
function of the number of participating nucleons gives a value of 1.13+-0.03
for the exponent. The mean transverse momentum, , of photons determined
from the ratio of the measured electromagnetic transverse energy and photon
multiplicity, remains almost constant with increasing rho_max. Results are
compared with model predictions.Comment: 16 pages including 4 figure
Pseudorapidity Distributions of Charged Particles in d + Au and p + p Collisions at = 200GeV
The measured pseudorapidity distributions of primary charged particles are
presented for d + Au and p + p collisions at 200 GeV
over a wide pseudorapidity range of 5.4. The results
for d + Au collisions are presented for minimum-bias events and as a function
of collision centrality. The measurements for p + p collisions are shown for
minimum-bias events. The ratio of the charged particle multiplicity in d + Au
and p + A collisions relative to that for inelastic p + p collisions is found
to depend only on , and it is remarkably independent of
collision energy and system mass. The deuteron and gold fragmentation regions
in d + Au collisions are in good agreement with proton nucleus data at lower
energies.Comment: 4 pages, 3 figures. To appear in the proceedings of Seventeenth
International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions
(Quark Matter 2004), Oakland, California from January 11-17, 2004. Submitted
to Journal of Physics G: Nuclear and Particle Physic
Centrality Dependence of Neutral Pion Production in 158 A GeV Pb + Pb Collisions
The production of neutral pions in 158AGeV Pb+Pb collisions has been studied
in the WA98 experiment at the CERN SPS. Transverse momentum spectra are studied
for the range 0.3 GeV/c < mT-m0 < 4.0 GeV/c. The results for central collisions
are compared to various models. The centrality dependence of the neutral pion
spectral shape and yield is investigated. An invariance of the spectral shape
and a simple scaling of the yield with the number of participating nucleons is
observed for centralities with greater than about 30 participating nucleons
which is most naturally explained by assuming an equilibrated system.Comment: 5 pages, Latex, including 3 eps figures, submitted to Phys.Rev.Lett;
updated pQCD comparison due to new input from the author, updated references,
corrected plotting error in figure
The Landscape of Particle Production: Results from PHOBOS
Recent results from the PHOBOS experiment at RHIC are presented, both from
Au+Au collisions from the 2001 run and p+p and d+Au collisions from 2003. The
centrality dependence of the total charged particle multiplicity in p+p and
d+Au show features, such as Npart-scaling and limiting fragmentation, similar
to p+A collisions at lower energies. Multiparticle physics in Au+Au is found to
be local in (pseudo)rapidity, both when observed by HBT correlations and by
forward-backward pseudorapidity correlations. The shape of elliptic flow in
Au+Au, measured over the full range of pseudorapidity, appears to have a very
weak centrality dependence. Identified particle ratios in d+Au reactions show
little difference between the shape of proton and anti-proton spectra, while
the absolute yields show an approximate m_T scaling.Comment: 8 Pages, 11 Figures, Plenary talk at Quark Matter 2004, Oakland, CA,
January 11-18, 200
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