6,842 research outputs found
Effective field theories for heavy quarkonium
We review recent theoretical developments in heavy quarkonium physics from
the point of view of Effective Field Theories of QCD. We discuss
Non-Relativistic QCD and concentrate on potential Non-Relativistic QCD. Our
main goal will be to derive QCD Schr\"odinger-like equations that govern the
heavy quarkonium physics in the weak and strong coupling regime. We also
discuss a selected set of applications, which include spectroscopy, inclusive
decays and electromagnetic threshold production.Comment: 162 pages, 30 figures, revised version, references added. Accepted
for publication in Reviews of Modern Physic
Renormalization group scaling in nonrelativistic QCD
We discuss the matching conditions and renormalization group evolution of
non-relativistic QCD. A variant of the conventional MS-bar scheme is proposed
in which a subtraction velocity nu is used rather than a subtraction scale mu.
We derive a novel renormalization group equation in velocity space which can be
used to sum logarithms of v in the effective theory. We apply our method to
several examples. In particular we show that our formulation correctly
reproduces the two-loop anomalous dimension of the heavy quark production
current near threshold.Comment: (27 pages, revtex
Mapping deuterated methanol toward L1544: I. Deuterium fraction and comparison with modeling
The study of deuteration in pre-stellar cores is important to understand the
physical and chemical initial conditions in the process of star formation. In
particular, observations toward pre-stellar cores of methanol and deuterated
methanol, solely formed on the surface of dust grains, may provide useful
insights on surface processes at low temperatures. Here we analyze maps of CO,
methanol, formaldehyde and their deuterated isotopologues toward a well-known
pre-stellar core. This study allows us to test current gas-dust chemical
models. Single-dish observations of CHOH, CHDOH, HCO,
H_2\,^{13}CO, HDCO, DCO and CO toward the prototypical pre-stellar
core L1544 were performed at the IRAM 30 m telescope. We analyze their column
densities, distributions, and compare these observations with gas-grain
chemical models. The maximum deuterium fraction derived for methanol is
[CHDOH]/[CHOH] 0.080.02, while the measured deuterium
fractions of formaldehyde at the dust peak are [HDCO]/[HCO]
0.030.02, [DCO]/[HCO] 0.040.03 and [DCO]/[HDCO]
1.20.3. Observations differ significantly from the predictions of
models, finding discrepancies between a factor of 10 and a factor of 100 in
most cases. It is clear though that to efficiently produce methanol on the
surface of dust grains, quantum tunneling diffusion of H atoms must be switched
on. It also appears that the currently adopted reactive desorption efficiency
of methanol is overestimated and/or that abstraction reactions play an
important role. More laboratory work is needed to shed light on the chemistry
of methanol, an important precursor of complex organic molecules in space.Comment: Accepted for publication in A&
Order alpha^3 ln(1/alpha) Corrections to Positronium Decays
The logarithmically enhanced alpha^3 ln(1/alpha) corrections to the para- and
orthopositronium decay widths are calculated in the framework of dimensionally
regularized nonrelativistic quantum electrodynamics.In the case of
parapositronium, the correction is negative, approximately doubles the effect
of the leading logarithmic alpha^3 ln^2(1/alpha) one, and is comparable to the
nonlogarithmic O(alpha^2) one. As for orthopositronium, the correction is
positive and almost cancels the alpha^3 ln^2(1/alpha) one. The uncertainties in
the theoretical predictions for the decay widths are reduced.Comment: 10 pages (Latex); missing term added, corrected coefficient B_p used,
numerical results insignificantly change
Techniques in Analytic Lamb Shift Calculations
Quantum electrodynamics has been the first theory to emerge from the ideas of
regularization and renormalization, and the coupling of the fermions to the
virtual excitations of the electromagnetic field. Today, bound-state quantum
electrodynamics provides us with accurate theoretical predictions for the
transition energies relevant to simple atomic systems, and steady theoretical
progress relies on advances in calculational techniques, as well as numerical
algorithms. In this brief review, we discuss one particular aspect connected
with the recent progress: the evaluation of relativistic corrections to the
one-loop bound-state self-energy in a hydrogenlike ion of low nuclear charge
number, for excited non-S states, up to the order of alpha (Zalpha)^6 in units
of the electron mass. A few details of calculations formerly reported in the
literature are discussed, and results for 6F, 7F, 6G and 7G states are given.Comment: 16 pages, LaTe
The QCD Potential at
Within an effective field theory framework, we obtain an expression for the
next-to-leading term in the expansion of the singlet QCD
potential in terms of Wilson loops, which holds beyond perturbation theory. The
ambiguities in the definition of the QCD potential beyond leading order in
are discussed and a specific expression for the potential is given.
We explicitly evaluate this expression at one loop and compare the outcome with
the existing perturbative results. On general grounds we show that for quenched
QED and fully Abelian-like models this expression exactly vanishes.Comment: 19 pages, LaTeX, 1 figure. Journal version. Discussion refined,
misprints corrected, few references added; results unchange
Three-Loop Anomalous Dimension of the Heavy Quark Pair Production Current in Non-Relativistic QCD
The three-loop non-mixing contributions to the anomalous dimension of the
leading order quark pair production current in non-relativistic QCD are
computed. It is demonstrated that the renormalization procedure can only be
carried out consistently if the dynamics of both soft and the ultrasoft degrees
of freedom is present for all scales below the heavy quark mass, and if the
soft and ultrasoft renormalization scales are always correlated.Comment: 19 pages, revtex, 5 postscript figures include
Running of the heavy quark production current and 1/k potential in QCD
The 1/k contribution to the heavy quark potential is first generated at one
loop order in QCD. We compute the two loop anomalous dimension for this
potential, and find that the renormalization group running is significant. The
next-to-leading-log coefficient for the heavy quark production current near
threshold is determined. The velocity renormalization group result includes the
alpha_s^3 ln^2(alpha_s) ``non-renormalization group logarithms'' of Kniehl and
Penin.Comment: 30 pages, journal versio
Renormalization group analysis of the QCD quark potential to order v^2
A one-loop renormalization group analysis of the order v^2 relativistic
corrections to the static QCD potential is presented. The velocity
renormalization group is used to simultaneously sum ln(m/mv) and ln(m/mv^2)
terms. The results are compared to previous calculations in the literature.Comment: 13 pages. important change: running of soft Lagrangian include
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