The critical region of strong-coupling lattice QCD in different large-N limits

We study the critical behavior at nonzero temperature phase transitions of an effective Hamiltonian derived from lattice QCD in the strong-coupling expansion. Following studies of related quantum spin systems that have a similar Hamiltonian, we show that for large $N_c$ and fixed $g^2N_c$, mean field scaling is not expected, and that the critical region has a finite width at $N_c=\infty$. A different behavior rises for $N_f\to \infty$ and fixed $N_c$ and $g^2/N_f$, which we study in two spatial dimensions and for $N_c=1$. We find that the width of the critical region is suppressed by $1/N_f^p$ with $p=1/2$, and argue that a generalization to $N_c>1$ and to three dimensions will change this only in detail (e.g. the value of $p>0$), but not in principle. We conclude by stating under what conditions this suppression is expected, and remark on possible realizations of this phenomenon in lattice gauge theories in the continuum.Comment: 24 pages, 6 figures. New version includes: a more extensive discussion of strong-coupling expansions and their region of validity. Accordingly I have reworded the descriptions of the investigated limits. Removed typos and misprint

Studies of highly-boosted top quarks near the TeV scale using jet masses at the LHC

Studies of highly-boosted top quarks produced inclusively in pp collisions at 14 TeV are discussed. The hadronic decays of boosted top quarks was studied in a data-driven approach by analysing shapes of jet-mass distributions. Using Monte Carlo models after a fast detector simulation, it is shown that inclusive production of boosted top quarks can be observed if it has a cross section at least twice larger than the prediction from the approximate next-to-next-to-leading-order (aNNLO) calculation for the ttbar process. The ttbar process with the nominal aNNLO strength can be measured using the masses of jets after a b-tagging.Comment: 11 pages, 5 figure

Oscillating Superfluidity of Bosons in Optical Lattices

We follow up on a recent suggestion by C. Orzel et. al., Science, 291, 2386 (2001), whereby bosons in an optical lattice would be subjected to a sudden parameter change from the Mott to the superfluid phase. We analyze the Bose Hubbard model with a modified coherent states path integral which can escribe - both - phases. The saddle point theory yields collective oscillations of the uniform superfluid order parameter. These would be seen in time resolved interference patterns made by the released gas. We calculate the collective oscillation's damping rate by phason pair emission. In two dimensions the overdamped region largely overlaps with the quantum critical region. Measurements of critical dynamics on the Mott side are proposed.Comment: 4 pages 1 eps figures; Final version as appears in PRL. Added discussion on spontaneous generation of vortice

Will the Real Excess Burden Please Stand Up? (Or, Seven Measures in Search of a Concept)

It is well understood that a tax which distorts relative prices generates a welfare cost or "excess burden" in addition to any associated transfer of resources, but there remains considerable controversy and confusion with respect to procedures for measuring this excess burden. The purpose of this paper is to clarify matters concerning what is one of the most basic concepts in welfare economics. We describe and evaluate a number of alternative conceptual experiments which might lie behind an excess burden calculation, showing how these notions can be represented graphically and algebraically and how they can be approximated numerically.

Spin pumping by a field-driven domain wall

We calculate the charge current in a metallic ferromagnet to first order in the time derivative of the magnetization direction. Irrespective of the microscopic details, the result can be expressed in terms of the conductivities of the majority and minority electrons and the non-adiabatic spin transfer torque parameter $\beta$. The general expression is evaluated for the specific case of a field-driven domain wall and for that case depends strongly on the ratio of $\beta$ and the Gilbert damping constant. These results may provide an experimental method to determine this ratio, which plays a crucial role for current-driven domain-wall motion.Comment: 4 pages, 1 figure v2: some typos corrected v3: published versio

Paramagnon-induced dispersion anomalies in the cuprates

We report the self-energy associated with RPA magnetic susceptibility in the hole-doped Bi_2Sr_2CuO_6 (Bi2201) and the electron-doped Nd_{2-x}Ce_xCuO_4 (NCCO) in the overdoped regime within the framework of a one-band Hubbard model. Strong weight is found in the magnetic spectrum around (pi, 0) at about 360 meV in Bi2201 and 640 meV in NCCO, which yields dispersion anomalies in accord with the recently observed `waterfall' effects in the cuprates.Comment: Submitted to PRL, Dec. 21, 2006; 4 eps figures, revte

Antiferromagnetic Spinor Condensates are Quantum Rotors

We establish a theoretical correspondence between spin-one antiferromagnetic spinor condensates in an external magnetic field and quantum rotor models in an external potential. We show that the rotor model provides a conceptually clear picture of the possible phases and dynamical regimes of the antiferromagnetic condensate. We also show that this mapping simplifies calculations of the condensate's spectrum and wavefunctions. We use the rotor mapping to describe the different dynamical regimes recently observed in $^{23}$Na condensates. We also suggest a way to experimentally observe quantum mechanical effects (collapse and revival) in spinor condensates.Comment: minor revisions. some typos correcte

Optimal Tc_c of cuprates: role of screening and reservoir layers

We explore the role of charge reservoir layers (CRLs) on the superconducting transition temperature of cuprate superconductors. Specifically, we study the effect of CRLs with efficient short distance dielectric screening coupled capacitively to copper oxide metallic layers. We argue that dielectric screening at short distances and at frequencies of the order of the superconducting gap, but small compared to the Fermi energy can significantly enhance T$_c$, the transition temperature of an unconventional superconductor. We discuss the relevance of our qualitative arguments to a broader class of unconventional superconductors.Comment: 8 Pages, 4 figure