548 research outputs found
V(us) Determination from Hyperon Semileptonic Decays
We analyze the numerical determination of the quark mixing factor V(us) from
hyperon semileptonic decays. The discrepancies between the results obtained in
two previous studies are clarified. Our fits indicate sizeable SU(3) breaking
corrections, which unfortunately can only be fully determined from the data at
the first order. The lack of a reliable theoretical calculation of second-order
symmetry breaking effects translates into a large systematic uncertainty, which
has not been taken into account previously. Our final result, V(us) = 0.226 +/-
0.005, is not competitive with the existing determinations from K(l3), K(l2)
and \tau decays.Comment: 16 pages, no figures. References added and other minor change
Unintentional F doping of the surface of SrTiO3(001) etched in HF acid -- structure and electronic properties
We show that the HF acid etch commonly used to prepare SrTiO3(001) for
heteroepitaxial growth of complex oxides results in a non-negligible level of F
doping within the terminal surface layer of TiO2. Using a combination of x-ray
photoelectron spectroscopy and scanned angle x-ray photoelectron diffraction,
we determine that on average ~13 % of the O anions in the surface layer are
replaced by F, but that F does not occupy O sites in deeper layers. Despite
this perturbation to the surface, the Fermi level remains unpinned, and the
surface-state density, which determines the amount of band bending, is driven
by factors other than F doping. The presence of F at the STO surface is
expected to result in lower electron mobilities at complex oxide
heterojunctions involving STO substrates because of impurity scattering.
Unintentional F doping can be substantially reduced by replacing the HF-etch
step with a boil in deionized water, which in conjunction with an oxygen tube
furnace anneal, leaves the surface flat and TiO2 terminated.Comment: 18 pages, 7 figure
Stochastic Calculus for a Time-changed Semimartingale and the Associated Stochastic Differential Equations
It is shown that under a certain condition on a semimartingale and a
time-change, any stochastic integral driven by the time-changed semimartingale
is a time-changed stochastic integral driven by the original semimartingale. As
a direct consequence, a specialized form of the Ito formula is derived. When a
standard Brownian motion is the original semimartingale, classical Ito
stochastic differential equations driven by the Brownian motion with drift
extend to a larger class of stochastic differential equations involving a
time-change with continuous paths. A form of the general solution of linear
equations in this new class is established, followed by consideration of some
examples analogous to the classical equations. Through these examples, each
coefficient of the stochastic differential equations in the new class is given
meaning. The new feature is the coexistence of a usual drift term along with a
term related to the time-change.Comment: 27 pages; typos correcte
Equidistribution of zeros of holomorphic sections in the non compact setting
We consider N-tensor powers of a positive Hermitian line bundle L over a
non-compact complex manifold X. In the compact case, B. Shiffman and S.
Zelditch proved that the zeros of random sections become asymptotically
uniformly distributed with respect to the natural measure coming from the
curvature of L, as N tends to infinity. Under certain boundedness assumptions
on the curvature of the canonical line bundle of X and on the Chern form of L
we prove a non-compact version of this result. We give various applications,
including the limiting distribution of zeros of cusp forms with respect to the
principal congruence subgroups of SL2(Z) and to the hyperbolic measure, the
higher dimensional case of arithmetic quotients and the case of orthogonal
polynomials with weights at infinity. We also give estimates for the speed of
convergence of the currents of integration on the zero-divisors.Comment: 25 pages; v.2 is a final update to agree with the published pape
Relativistic Mass Ejecta from Phase-transition-induced Collapse of Neutron Stars
We study the dynamical evolution of a phase-transition-induced collapse
neutron star to a hybrid star, which consists of a mixture of hadronic matter
and strange quark matter. The collapse is triggered by a sudden change of
equation of state, which result in a large amplitude stellar oscillation. The
evolution of the system is simulated by using a 3D Newtonian hydrodynamic code
with a high resolution shock capture scheme. We find that both the temperature
and the density at the neutrinosphere are oscillating with acoustic frequency.
However, they are nearly 180 out of phase. Consequently, extremely
intense, pulsating neutrino/antineutrino fluxes will be emitted periodically.
Since the energy and density of neutrinos at the peaks of the pulsating fluxes
are much higher than the non-oscillating case, the electron/positron pair
creation rate can be enhanced dramatically. Some mass layers on the stellar
surface can be ejected by absorbing energy of neutrinos and pairs. These mass
ejecta can be further accelerated to relativistic speeds by absorbing
electron/positron pairs, created by the neutrino and antineutrino annihilation
outside the stellar surface. The possible connection between this process and
the cosmological Gamma-ray Bursts is discussed.Comment: 40 pages, 11 figures, accepted for publication in JCA
Non-Centrosymmetric Heavy-Fermion Superconductors
In this chapter we discuss the physical properties of a particular family of
non-centrosymmetric superconductors belonging to the class heavy-fermion
compounds. This group includes the ferromagnet UIr and the antiferromagnets
CeRhSi3, CeIrSi3, CeCoGe3, CeIrGe3 and CePt3Si, of which all but CePt3Si become
superconducting only under pressure. Each of these superconductors has
intriguing and interesting properties. We first analyze CePt3Si, then review
CeRhSi3, CeIrSi3, CeCoGe3 and CeIrGe3, which are very similar to each other in
their magnetic and electrical properties, and finally discuss UIr. For each
material we discuss the crystal structure, magnetic order, occurrence of
superconductivity, phase diagram, characteristic parameters, superconducting
properties and pairing states. We present an overview of the similarities and
differences between all these six compounds at the end.Comment: To appear in "Non-Centrosymmetric Superconductors: Introduction and
Overview", Lecture Notes in Physics 847, edited by E. Bauer and M. Sigrist
(Springer-Verlag, Berlin Heidelberg, 2012) Chap. 2, pp. 35-7
Heavy Quarks and Heavy Quarkonia as Tests of Thermalization
We present here a brief summary of new results on heavy quarks and heavy
quarkonia from the PHENIX experiment as presented at the "Quark Gluon Plasma
Thermalization" Workshop in Vienna, Austria in August 2005, directly following
the International Quark Matter Conference in Hungary.Comment: 8 pages, 5 figures, Quark Gluon Plasma Thermalization Workshop
(Vienna August 2005) Proceeding
Single Electrons from Heavy Flavor Decays in p+p Collisions at sqrt(s) = 200 GeV
The invariant differential cross section for inclusive electron production in
p+p collisions at sqrt(s) = 200 GeV has been measured by the PHENIX experiment
at the Relativistic Heavy Ion Collider over the transverse momentum range $0.4
<= p_T <= 5.0 GeV/c at midrapidity (eta <= 0.35). The contribution to the
inclusive electron spectrum from semileptonic decays of hadrons carrying heavy
flavor, i.e. charm quarks or, at high p_T, bottom quarks, is determined via
three independent methods. The resulting electron spectrum from heavy flavor
decays is compared to recent leading and next-to-leading order perturbative QCD
calculations. The total cross section of charm quark-antiquark pair production
is determined as sigma_(c c^bar) = 0.92 +/- 0.15 (stat.) +- 0.54 (sys.) mb.Comment: 329 authors, 6 pages text, 3 figures. Submitted to Phys. Rev. Lett.
Plain text data tables for the points plotted in figures for this and
previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
Nuclear Modification of Electron Spectra and Implications for Heavy Quark Energy Loss in Au+Au Collisions at sqrt(s_NN)=200 GeV
The PHENIX experiment has measured mid-rapidity transverse momentum spectra
(0.4 < p_T < 5.0 GeV/c) of electrons as a function of centrality in Au+Au
collisions at sqrt(s_NN)=200 GeV. Contributions from photon conversions and
from light hadron decays, mainly Dalitz decays of pi^0 and eta mesons, were
removed. The resulting non-photonic electron spectra are primarily due to the
semi-leptonic decays of hadrons carrying heavy quarks. Nuclear modification
factors were determined by comparison to non-photonic electrons in p+p
collisions. A significant suppression of electrons at high p_T is observed in
central Au+Au collisions, indicating substantial energy loss of heavy quarks.Comment: 330 authors, 6 pages text, 3 figures. Submitted to Phys. Rev. Lett.
Plain text data tables for the points plotted in figures for this and
previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
Formation of dense partonic matter in relativistic nucleus-nucleus collisions at RHIC: Experimental evaluation by the PHENIX collaboration
Extensive experimental data from high-energy nucleus-nucleus collisions were
recorded using the PHENIX detector at the Relativistic Heavy Ion Collider
(RHIC). The comprehensive set of measurements from the first three years of
RHIC operation includes charged particle multiplicities, transverse energy,
yield ratios and spectra of identified hadrons in a wide range of transverse
momenta (p_T), elliptic flow, two-particle correlations, non-statistical
fluctuations, and suppression of particle production at high p_T. The results
are examined with an emphasis on implications for the formation of a new state
of dense matter. We find that the state of matter created at RHIC cannot be
described in terms of ordinary color neutral hadrons.Comment: 510 authors, 127 pages text, 56 figures, 1 tables, LaTeX. Submitted
to Nuclear Physics A as a regular article; v3 has minor changes in response
to referee comments. Plain text data tables for the points plotted in figures
for this and previous PHENIX publications are (or will be) publicly available
at http://www.phenix.bnl.gov/papers.htm
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