Fragmentation Functions for Lepton Pairs

We calculate the fragmentation function for a light quark to decay into a lepton pair to leading order in the QCD coupling constant. In the formal definition of the fragmentation function, a QED phase must be included in the eikonal factor to guarantee QED gauge invariance. We find that the longitudinal polarization fraction is a decreasing function of the factorization scale, in accord with the intuitive expectation that the virtual photon should behave more and more like a real photon as the transverse momomentum of the fragmenting quark increases.Comment: 13 pages, 4 figures, normalization corrected, text abbreviate

Searching for BcB_c mesons in the ATLAS experiment at LHC

We discuss the feasibility of the observation of the signal from $B_c$ mesons in the ATLAS experiment of the LHC collider at a luminosity of ${\approx}\ 10^{33}$cm$^{-2}$s$^{-1}$. In particular we address the decay mode$B_c{\rightarrow}J/\psi \pi$followed by the leptonic decay$J/\psi{\rightarrow}\mu^+\mu^-$, which should permit an accurate measurement of the$B_c$mass. We performed a Monte Carlo study of the signal and background concluding that a precision of$40$MeV for the$B_c$ mass could be achieved after one year of running.Comment: Latex,7 pages including 3 uuencoded Postscript figures appended at the end of the latex fil

The neutrino emission due to plasmon decay and neutrino luminosity of white dwarfs

One of the effective mechanisms of neutrino energy losses in red giants, presupernovae and in the cores of white dwarfs is the emission of neutrino-antineutrino pairs in the process of plasmon decay. In this paper, we numerically calculate the emissivity due to plasmon decay in a wide range of temperatures (10^7-10^11) K and densities (200-10^14) g cm^-3. Numerical results are approximated by convenient analytical expressions. We also calculate and approximate by analytical expressions the neutrino luminosity of white dwarfs due to plasmon decay, as a function of their mass and internal temperature. This neutrino luminosity depends on the chemical composition of white dwarfs only through the parameter mu_e (the net number of baryons per electron) and is the dominant neutrino luminosity in all white dwarfs at the neutrino cooling stage.Comment: 19 pages, 3 figures, accepted for publication in MNRA

The Massive Thermal Basketball Diagram

The "basketball diagram" is a three-loop vacuum diagram for a scalar field theory that cannot be expressed in terms of one-loop diagrams. We calculate this diagram for a massive scalar field at nonzero temperature, reducing it to expressions involving three-dimensional integrals that can be easily evaluated numerically. We use this result to calculate the free energy for a massive scalar field with a phi^4 interaction to three-loop order.Comment: 19 pages, 3 figure

Collective Dynamics of Solitons and Inequivalent Quantizations

The collective dynamics of solitons with a coset space G/H as moduli space is studied. It is shown that the collective band for a vibrational state is given by the inequivalent coset space quantization corresponding to the representation of H carried by the vibration.Comment: 6 pages, revte

Damping rate of plasmons and photons in a degenerate nonrelativistic plasma

A calculation is presented of the plasmon and photon damping rates in a dense nonrelativistic plasma at zero temperature, following the resummation program of Braaten-Pisarski. At small soft momentum $k$, the damping is dominated by $3 \to 2$ scattering processes corresponding to double longitudinal Landau damping. The dampings are proportional to $(\alpha/v_{F})^{3/2} k^2/m$, where $v_{F}$ is the Fermi velocity.Comment: 9 pages, 2 figure

Comment on ``High Temperature Fermion Propagator -- Resummation and Gauge Dependence of the Damping Rate''

Baier et al. have reported the damping rate of long-wavelength fermionic excitations in high-temperature QED and QCD to be gauge-fixing-dependent even within the resummation scheme due to Braaten and Pisarski. It is shown that this problem is caused by the singular nature of the on-shell expansion of the fermion self-energy in the infra-red. Its regularization reveals that the alleged gauge dependence pertains to the residue rather than the pole of the fermion propagator, so that in particular the damping constant comes out gauge-independent, as it should.Comment: 5 page

A Slavnov-Taylor identity and equality of damping rates for static transverse and longitudinal gluons in hot QCD

A Slavnov-Taylor identity is derived for the gluon polarization tensor in hot QCD. We evaluate its implications for damping of gluonic modes in the plasma. Applying the identity to next to the leading order in hard-thermal-loop resummed perturbation theory, we derive the expected equality of damping rates for static transverse and longitudinal (soft) gluons. This is of interest also in view of deviating recent reports of $\gamma_t(p=0)\neq\gamma_l(p=0)$ based on a direct calculation of $\gamma_l(p=0)$.Comment: 13 pages, 1 figure, LaTe

Color-Octet Fragmentation and the psi' Surplus at the Tevatron

The production rate of prompt $\psi'$'s at large transverse momentum at the Tevatron is larger than theoretical expectations by about a factor of 30. As a solution to this puzzle, we suggest that the dominant $\psi'$ production mechanism is the fragmentation of a gluon into a $c \bar c$ pair in a pointlike color-octet S-wave state, which subsequently evolves nonperturbatively into a $\psi'$ plus light hadrons. The contribution to the fragmentation function from this process is enhanced by a short-distance factor of $1/\alpha_s^2$ relative to the conventional color-singlet contribution. This may compensate for the suppression by $v^4$, where $v$ is the relative momentum of the charm quark in the $\psi'$. If this is indeed the dominant production mechanism at large $p_T$, then the prompt $\psi'$'s that are observed at the Tevatron should almost always be associated with a jet of light hadrons.Comment: 9 pages, LaTe