Global hyperon polarization at local thermodynamic equilibrium with vorticity, magnetic field and feed-down

The system created in ultrarelativistic nuclear collisions is known to behave as an almost ideal liquid. In non-central collisions, due to the large orbital momentum, such a system might be the fluid with the highest vorticity ever created under laboratory conditions. Particles emerging from such a highly vorticous fluid are expected to be globally polarized with their spins on average pointing along the system angular momentum. Vorticity-induced polarization is the same for particles and antiparticles, but the intense magnetic field generated in these collisions may lead to the splitting in polarization. In this paper we outline the thermal approach to the calculation of the global polarization phenomenon for particles with spin and we discuss the details of the experimental study of this phenomenon, estimating the effect of feed-down. A general formula is derived for the polarization transfer in two-body decays and, particularly, for strong and electromagnetic decays. We find that accounting for such effects is crucial when extracting vorticity and magnetic field from the experimental data.Comment: 14 pages, 1 figure. Final version published in PRC with one more formula and slightly revised tex

On the π\pi and KK as qqˉq \bar q Bound States and Approximate Nambu-Goldstone Bosons

We reconsider the two different facets of $\pi$ and $K$ mesons as $q \bar q$ bound states and approximate Nambu-Goldstone bosons. We address several topics, including masses, mass splittings between $\pi$ and $\rho$ and between $K$ and $K^*$, meson wavefunctions, charge radii, and the $K-\pi$ wavefunction overlap.Comment: 15 pages, late

Decay of metastable current states in one-dimensional resonant tunneling devices

Current switching in a double-barrier resonant tunneling structure is studied in the regime where the current-voltage characteristic exhibits intrinsic bistability, so that in a certain range of bias two different steady states of current are possible. Near the upper boundary V_{th} of the bistable region the upper current state is metastable, and because of the shot noise it eventually decays to the stable lower current state. We find the time of this switching process in strip-shaped devices, with the width small compared to the length. As the bias V is tuned away from the boundary value V_{th} of the bistable region, the mean switching time \tau increases exponentially. We show that in long strips \ln\tau \propto (V_{th} -V)^{5/4}, whereas in short strips \ln\tau \propto (V_{th} -V)^{3/2}. The one-dimensional geometry of the problem enables us to obtain analytically exact expressions for both the exponential and the prefactor of \tau. Furthermore, we show that, depending on the parameters of the system, the switching can be initiated either inside the strip, or at its ends.Comment: 12 pages, 5 figures, update to published versio

Quenched disorder induced magnetization jumps in (Sm,Sr)MnO3_3

Magnetic field induced step-like changes in magnetization and resistivity of SmSr manganites were studied. A strong dependence of these features on the cooling rate was observed. Magnetostriction, however, does not show the presence of large strain in our samples. From all these features we can rule out the conventional explanation of magnetization jumps as a consequence of martensitic transition. We propose instead that quenched by fast cooling disorder leads to the formation of an inhomogeneous metastable state and to subsequent magnetization jumps.Comment: 4 pages, 4 figures, to be published in PRB Brief

Multiparticle tree amplitudes in scalar field theory

Following an argument advanced by Feynman, we consider a method for obtaining the effective action which generates the sum of tree diagrams with external physical particles. This technique is applied, in the unbroken \lambda \phi^4 theory, to the derivation of the threshold amplitude for the production of $n$ scalar particles by $n$ initial particles. The leading contributions to the tree amplitude, which become singular in the threshold limit, exhibit a factorial growth with n.Comment: uuencoded gz-compressed file created by csh script uufile

Hadronic Spectral Moments in Semileptonic B Decays With a Lepton Energy Cut

We compute the first two moments of the final hadronic invariant mass in inclusive semileptonic B decay, in the presence of a cut on the charged lepton energy. These moments may be measured directly by experiments at the Upsilon(4S) using the neutrino reconstruction technique, which requires such a cut. Measurement of these moments will place constraints on the nonperturbative parameters \bar\Lambda and \lambda_1, which are relevant for extracting the quark masses m_b and m_c, as well as the CKM angle V_cb. We include terms of order \alpha_s^2\beta_0 and 1/m_b^3 in the operator product expansion, and use the latter to estimate the theoretical uncertainty in the extraction of \bar\Lambda and \lambda_1.Comment: 13 pages, 5 figures, REVTe