878 research outputs found
Two-loop QCD Corrections to Transitions at Zero Recoil: Analytical Results
We present analytical results for the contributions to the
functions and which parameterize QCD corrections to
semileptonic transitions at zero recoil. Previously obtained
approximate results are confirmed. The methods of computing the relevant
two-loop diagrams with two mass scales are discussed in some detail.Comment: 19 pages, late
Non-Abelian Dipole Radiation and the Heavy Quark Expansion
Dipole radiation in QCD is derived to the second order in . A
power-like evolution of the spin-singlet heavy quark operators is obtained to
the same accuracy. In particular, relation between a
short-distance low-scale running heavy quark mass and the \barMS mass is
given. We discuss the properties of the effective QCD coupling \aw(E) which
governs the dipole radiation. This coupling is advantageous for heavy quark
physics.Comment: 12 pages, Late
Lambda<0 Quantum Gravity in 2+1 Dimensions II: Black Hole Creation by Point Particles
Using the recently proposed formalism for Lambda<0 quantum gravity in 2+1
dimensions we study the process of black hole production in a collision of two
point particles. The creation probability for a BH with a simplest topology
inside the horizon is given by the Liouville theory 4-point function projected
on an intermediate state. We analyze in detail the semi-classical limit of
small AdS curvatures, in which the probability is dominated by the exponential
of the classical Liouville action. The probability is found to be exponentially
small. We then argue that the total probability of creating a horizon given by
the sum of probabilities of all possible internal topologies is of order unity,
so that there is no exponential suppression of the total production rate.Comment: v1: 30+1 pages, figures, v2: 34+1 pages, agruments straightened ou
The b quark low-scale running mass from Upsilon sum rules
The b quark low-scale running mass m_kin is determined from an analysis of
the Upsilon sum rules in the next-to-next-to-leading order (NNLO). It is
demonstrated that using this mass one can significantly improve the convergence
of the perturbation series for the spectral density moments. We obtain m_kin(1
GeV) = 4.56 \pm 0.06 GeV. Using this result we derive the value of the MS-bar
mass m: m(m) = 4.20 \pm 0.1 GeV. Contrary to the low-scale running mass, the
pole mass of the b quark cannot be reliably determined from the sum rules. As a
byproduct of our study we find the NNLO analytical expression for the cross
section e+e- --> Q\bar Q of the quark antiquark pair production in the
threshold region, as well as the energy levels and the wave functions at the
origin for the ^1S_3 bound states of Q\bar Q.Comment: 22 pages, Late
Higgs boson production at hadron colliders in NNLO QCD
We compute the total cross-section for direct Higgs boson production in
hadron collisions at NNLO in perturbative QCD. A new technique which allows us
to perform an algorithmic evaluation of inclusive phase-space integrals is
introduced, based on the Cutkosky rules, integration by parts and the
differential equation method for computing master integrals. Finally, we
discuss the numerical impact of the O(alpha_s^2) QCD corrections to the Higgs
boson production cross-section at the LHC and the Tevatron.Comment: 27 pages, revte
Applicability of energy storage units to electric transport
The paper analyzes the possibility for replacement hydrocarbon fuels by energy storage devices in transport. The technical characteristics of the modern batteries and ultracapacitors are presented, their specific parameters are estimated. Energy and power requirements for various driving styles of the vehicles are estimated. The determination of requirements for energy storage devices and the evaluation of applicability of energy storage units are demonstrated in the article
Correlation Functions and Cumulants in Elliptic Flow Analysis
We consider various methods of flow analysis in heavy ion collisions and
compare experimental data on corresponding observables to the predictions of
our saturation model proposed earlier. We demonstrate that, due to the nature
of the standard flow analysis, azimuthal distribution of particles with respect
to reaction plane determined from the second order harmonics should always be
proportional to independent of the physical origin of
particle correlations (flow or non-flow). The amplitude of this distribution is
always physical and proportional to . Two-particle correlations analysis
is therefore a more reliable way of extracting the shape of physical azimuthal
anisotropy. We demonstrate that two-particle correlation functions generated in
our minijet model of particle production are in good agreement with the data
reported by PHENIX. We discuss the role of non-flow correlations in the
cumulant flow analysis and demonstrate using a simple example that if the flow
is weak, higher order cumulants analysis does not significantly reduce the
contribution of non-flow correlations to elliptic flow observable in RHIC
data.Comment: 18 pages, 1 figure; v2: IR safety and v2(pT) from 4th order cumulant
discussions adde
Two-loop QCD corrections to the heavy quark pair production cross section in e+e- annihilation near the threshold
We present the O(alpha_s) corrections to the cross section for the reaction
e+e- --> gamma^* --> Q \bar Q in the energy region close to the threshold. We
assume that the energy of the reaction is such that both the perturbative
expansion in the strong coupling constant and expansion in the relative
velocity of the heavy quarks can be used. We explicitly obtain terms
O(alpha_s^2/beta^2, alpha_s^2/beta, alpha_s^2) in the relative correction to
the threshold cross section. Using the ideas of asymptotic expansions, we
demonstrate how an expansion of Feynman diagrams in the threshold region is
constructed. From this analysis we obtain a matching relation between the
vector current in full QCD and the quark-antiquark current in NRQCD at leading
order in 1/m and the second order in the strong coupling constant.Comment: 9 pages, revte
Second order QCD corrections to inclusive semileptonic b \to Xc l \bar \nu_l decays with massless and massive lepton
We extend previous computations of the second order QCD corrections to
semileptonic b \to c inclusive transitions, to the case where the charged
lepton in the final state is massive. This allows accurate description of b \to
c \tau \bar \nu_\tau decays. We review techniques used in the computation of
O(\alpha_s^2) corrections to inclusive semileptonic b \to c transitions and
present extensive numerical studies of O(\alpha_s^2) QCD corrections to b \to c
l \bar \nu_l decays, for l =e, \tau.Comment: 30 pages, 4 figures, 5 table
O(\alpha_s^2) corrections to semileptonic decay b \to c l \bar \nu_l
We compute the next-to-next-to-leading order (NNLO) QCD corrections to b \to
c l \bar \nu_l decay rate at a fully differential level. Arbitrary cuts on
kinematic variables of the decay products can be imposed. Our computation can
be used to study the NNLO QCD corrections to the total decay rate as well as to
the lepton energy, hadronic invariant mass and hadronic energy moments and to
incorporate those corrections into global fits of inclusive semileptonic
B-decays.Comment: 5 pages, revte
- …