The Chiral Soliton Model for Arbitrary Colors and Flavors
The quantum numbers of the chiral soliton are derived for an arbitrary number of colors and flavors.
hep-ph↗
arXiv subjects
Aneesh V. Manohar
Publications and source records attributed to Aneesh V. Manohar.
Enhanced Nonperturbative Effects in Z Decays to Hadrons
We use soft collinear effective field theory (SCET) to study nonperturbative strong interaction effects in Z decays to hadronic final states that are enhanced in corners of phase space. These occur, for example, in the jet energy distribution for two jet events near E_J=M_Z/2, the thrust distribution near unity and the jet invariant mass distribution near zero. The extent to which such nonperturbative effects for different observables are related is discussed.
hep-ph↗
Baryon Exotics in the Quark Model, the Skyrme Model and QCD
We identify the quantum numbers of baryon exotics in the Quark Model, the Skyrme Model and QCD, and show that they agree for arbitrary colors and flavors. We define exoticness, E, which can be used to classify the states. The exotic baryons include the recently discovered qqqq qbar pentaquarks (E=1), as well as exotic baryons with additional q qbar pairs (E >=1). The mass formula for non-exotic and exotic baryons is given as an expansion in 1/N, and allows one to relate the moment of inertia of the Skyrme soliton to the mass of a constituent quark.
hep-ph↗
The Orthopositronium Decay Spectrum using NRQED
The photon spectrum in orthopositronium to 3 gamma decay is computed using effective field theory methods. For energetic photons, the spectrum agrees with the Ore-Powell result, but deviates from it when the photon energy is comparable to the positronium binding energy. The decay spectrum in this region depends on a positronium structure function, which is computed in this paper. At still lower energies the photon spectrum is dominated by the parapositronium resonance contribution. Our results are compatible with Low's theorem on soft photon emission.
hep-ph↗
Deep inelastic scattering as x -> 1 using soft-collinear effective theory
Soft-collinear effective theory (SCET) is used to sum Sudakov double-logarithms in the x ->1 endpoint region for the deep inelastic scattering structure function. The calculations are done in both the target rest frame and the Breit frame. The separation of scales in the effective theory implies that the anomalous dimension of the SCET current is linear in ln mu, and the anomalous dimension for the Nth moment of the structure function is linear in ln N, to all orders in perturbation theory. The SCET formulation is shown to be free of Landau pole singularities. Some important differences between the deep inelastic structure function and the shape function in B decay are discussed.
hep-ph↗
Shape function effects in B -> X_s gamma and B -> X_u l nu decays
We calculate the decay distributions for inclusive B -> X_s gamma and B -> X_u l nu decays in the endpoint region, where radiative corrections are large. The computation is done using effective field theory methods. The matching coefficients are computed to O(alpha_s), and the anomalous dimensions to next-to-leading order. The final expressions for the differential decay spectra include the complete O(alpha_s) corrections, and sum the leading and next-to-leading Sudakov series. We present results for regions of phase space where the shape function can be expanded in local operators, and give the matching coefficients of the resulting enhanced non-perturbative effects to order alpha_s. We show that moments of the shape function {\it are not} given by moments of local operators once perturbative effects are included, explain why the shape function and its moments satisfy different renormalization group equations, and contrast this with the situation for deep inelastic scattering. We show that there are large perturbative corrections in the usual definition of the shape function. This renders incorrect previous prescriptions for combining radiative corrections with the shape function.
hep-ph↗
Enhanced nonperturbative effects in jet distributions
We consider the triple differential distribution dΓ/(dE_J)(dm_J^2)(dΩ_J) for two-jet events at center of mass energy M, smeared over the endpoint region m_J^2 << M^2, |2 E_J -M| ~ Δ, \lqcd << Δ<< M. The leading nonperturbative correction, suppressed by \lqcd/Δ, is given by the matrix element of a single operator. A similar analysis is performed for three jet events, and the generalization to any number of jets is discussed. At order \lqcd/Δ, non-perturbative effects in four or more jet events are completely determined in terms of two matrix elements which can be measured in two and three jet events.
hep-ph↗
B decay shape variables and the precision determination of |Vcb| and mb
We present expressions for shape variables of B decay distributions in several different mass schemes, to order $α_s^2β_0$ and (Lambda_{QCD}/mb)^3. Such observables are sensitive to the b quark mass and matrix elements in the heavy quark effective theory, and recent measurements allow precision determinations of some of these parameters. We perform a combined fit to recent experimental results from CLEO, BABAR, and DELPHI, and discuss the theoretical uncertainties due to nonperturbative and perturbative effects. We discuss the possible discrepancy between the OPE prediction, recent BABAR results and the measured branching fraction to D and D* states. We find |Vcb| = (40.8 +- 0.9) x 10^{-3} and mb^{1S} = 4.74 +- 0.10 GeV, where the errors are dominated by experimental uncertainties.
hep-ph↗
Isospin violation in e+ e- --> B Bbar
The ratio of the B+ B- and B0 B0bar production rates in e+ e- annihilation is computed as a function of the B meson velocity and BB* pi coupling constant, using a non-relativistic effective field theory.
hep-ph↗
Reparameterization Invariance for Collinear Operators
We discuss restrictions on operators in the soft-collinear effective theory (SCET) which follow from the ambiguity in the decomposition of collinear momenta and the freedom in the choice of light-like basis vectors $n$ and $\bar n$. Invariance of SCET under small changes in $n$ and/or $\bar n$ implies a symmetry of the effective theory that constrains the form of allowed operators with collinear fields. The restrictions occur at a given order in the power counting as well as between different orders. As an example, we present the complete set of higher order operators that are related to the collinear quark kinetic term.
hep-ph↗
Spontaneously Broken Spacetime Symmetries and Goldstone's Theorem
Goldstone's theorem states that there is a massless mode for each broken symmetry generator. It has been known for a long time that the naive generalization of this counting fails to give the correct number of massless modes for spontaneously broken spacetime symmetries. We explain how to get the right count of massless modes in the general case, and discuss examples involving spontaneously broken Poincare and conformal invariance.
hep-th↗
Testing the Cosmic Coincidence Problem and the Nature of Dark Energy
Dark energy models which alter the relative scaling behavior of dark energy and matter could provide a natural solution to the cosmic coincidence problem - why the densities of dark energy and dark matter are comparable today. A generalized class of dark energy models is introduced which allows non-canonical scaling of the ratio of dark matter and dark energy with the Robertson-Walker scale factor a(t). Upcoming observations, such as a high redshift supernova survey, application of the Alcock-Paczynski test to quasar pairs, and cluster evolution, will strongly constrain the relative scaling of dark matter and dark energy as well as the equation of state of the dark energy. Thus, whether there actually is a coincidence problem, and the extent of cosmic coincidence in the universe's recent past can be answered observationally in the near future. Determining whether today is a special time in the history of the universe will be a SNAP.
astro-ph↗
The Running Coulomb Potential and Lamb Shift in QCD
The QCD beta-function and the anomalous dimensions for the Coulomb potential and the static potential first differ at three loop order. We evaluate the three loop ultrasoft anomalous dimension for the Coulomb potential and give the complete three loop running. Using this result, we calculate the leading logarithmic Lamb shift for a heavy quark-antiquark bound state, which includes all contributions to the binding energies of the form mα_s^4(α_s lnα_s)^k, k\ge 0.
hep-ph↗
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.
hep-ph↗
Nonrelativistic Bound States in Quantum Field Theory
Nonrelativistic bound states are studied using an effective field theory. Large logarithms in the effective theory can be summed using the velocity renormalization group. For QED, one can determine the structure of the leading and next-to-leading order series for the energy, and compute corrections up to order alpha^8 ln^3 alpha, which are relevant for the present comparison between theory and experiment. For QCD, one can compute the velocity renormalization group improved quark potentials. Using these to compute the renormalization group improved t-tbar production cross-section near threshold gives a result with scale uncertainties of 2%, a factor of 10 smaller than existing fixed order calculations.
hep-lat↗
The renormalization group for correlated scales: one-stage versus two-stage running
Nonrelativistic bound states have two low energy scales, a soft scale mu_S of order mv and an ultrasoft scale mu_U of order mv^2. In two-stage running, the soft and ultrasoft scales are lowered from m to mv, and then the ultrasoft scale is lowered from mv to mv^2. In one-stage running, the two scales are lowered in a correlated way using a subtraction velocity. We compare these two methods of summing logarithms and show that only the correlated running in velocity space of the one-stage method correctly reproduces the logarithms in non-relativistic bound states in QED. The argument for one-stage running is general, and should apply to any system with correlated scales.
hep-ph↗
The QCD Coupling Constant
This paper presents a summary of the current status of determinations of the strong coupling constant alpha_s. A detailed description of the definition, scale dependence and inherent theoretical ambiguities is given. The various physical processes that can be used to determine alpha_s are reviewed and attention is given to the uncertainties, both theoretical and experimental.
hep-ph↗
The QCD heavy-quark potential to order v^2: one loop matching conditions
The one-loop QCD heavy quark potential is computed to order v^2 in the color singlet and octet channels. Several errors in the previous literature are corrected. To be consistent with the velocity power counting, the full dependence on |p' + p|/|p' - p| is kept. The matching conditions for the NRQCD one-loop potential are computed by comparing the QCD calculation with that in the effective theory. The graphs in the effective theory are also compared to terms from the hard, soft, potential, and ultrasoft regimes in the threshold expansion. The issue of off-shell versus on-shell matching and gauge dependence is discussed in detail for the 1/(m k) term in the potential. Matching on-shell gives a 1/(m k) potential that is gauge independent and does not vanish for QED.
hep-ph↗