Sumantra Chakravarty

Final-state pi pi interactions in Upsilon (3S)--> Upsilon (1S) pi pi.

The [ital m][sub [pi][pi]] spectrum and various angular distributions in [Upsilon](3[ital S])[r arrow][Upsilon](1[ital S])[pi][pi] are studied including the effects of the [pi][pi] phase shift in the [ital I]=[ital L]=0 channel using the lowest order amplitude in the pion momentum expansion. Our results are compared with the recent CLEO data, and we find good agreement except for the cos[theta][sub [pi]][sup *] distributions. We argue that the cos[theta][sub [pi]][sup *] distribution, contrary to other distributions, is sensitive to the higher order corrections in the pion momentum expansion. This argument is supported by using an ansatz for the amplitude which is of higher order in the pion momentum expansion and still satisfies the soft pion theorem.

Is Upsilon (3S) a pure S wave

Assuming the QCD multipole expansion is applicable to hadronic transitions of [Upsilon](3[ital S]) into lower level bottomonia, we consider the possibility that [Upsilon](3[ital S]) has a [ital D]-wave component. This assumption leads to a natural explanation of the [pi][pi] spectrum in [Upsilon](3[ital S])[r arrow][Upsilon](1[ital S])[pi][pi]. The consequences of this assumption on other hadronic and radiative transitions of [Upsilon](3[ital S]) are also discussed in the same context.

Linear response of charged and neutral semions

Abstract The semion model of superconductivity is analysed on cylinder × time . The linear response for both charged and neutral semions is calculated using the self-consistent field approximation, keeping translational invariance and gauge invariance manifest. We observe the Meissner effect for the charged system. The dispersion relations are also evaluated for these systems. For small momentum transfer, the neutral system is shown to support sound waves and the charged system is shown to support plasma oscillations.

Energy density in the Maxwell-Chern-Simons theory.

A two-dimensional nonrelativistic fermion system coupled to both electromagnetic gauge fields and Chern-Simons gauge fields is analysed. Polarization tensors relevant in the quantum Hall effect and anyon superconductivity are obtained as simple closed integrals and are evaluated numerically for all momenta and frequencies. The correction to the energy density is evaluated in the random phase approximation (RPA), by summing an infinite series of ring diagrams. It is found that the correction has significant dependence on the particle number density. In the context of anyon superconductivity, the energy density relative to the mean field value is minimized at a hole concentration per lattice plaquette (0.05�0.06)·(pca/h 2 where pc and a are the momentum cutoff and lattice constant, respectively. At the minimum the correction is about 5 % � 25 %, depending on the ratio 2mωc/p 2 where ωc is the frequency cutoff. In the Jain-Fradkin-Lopez picture of the fractional quantum Hall effect the RPA correction to the energy density is very large. It diverges logarithmically as the cutoff is removed, implying that corrections beyond RPA become important at large momentum and frequency.

Final-state \pi\pi interactions in \Upsilon(3S)\rightarrow\Upsilon(1S)\pi\pi

The [ital m][sub [pi][pi]] spectrum and various angular distributions in [Upsilon](3[ital S])[r arrow][Upsilon](1[ital S])[pi][pi] are studied including the effects of the [pi][pi] phase shift in the [ital I]=[ital L]=0 channel using the lowest order amplitude in the pion momentum expansion. Our results are compared with the recent CLEO data, and we find good agreement except for the cos[theta][sub [pi]][sup *] distributions. We argue that the cos[theta][sub [pi]][sup *] distribution, contrary to other distributions, is sensitive to the higher order corrections in the pion momentum expansion. This argument is supported by using an ansatz for the amplitude which is of higher order in the pion momentum expansion and still satisfies the soft pion theorem.

Isϒ(3S)a pureSwave

Assuming the QCD multipole expansion is applicable to hadronic transitions of [Upsilon](3[ital S]) into lower level bottomonia, we consider the possibility that [Upsilon](3[ital S]) has a [ital D]-wave component. This assumption leads to a natural explanation of the [pi][pi] spectrum in [Upsilon](3[ital S])[r arrow][Upsilon](1[ital S])[pi][pi]. The consequences of this assumption on other hadronic and radiative transitions of [Upsilon](3[ital S]) are also discussed in the same context.

Vortex production in a first-order phase transition at finite temperature

Abstract We simulate the production of vortices in a first-order phase transition at finite temperature. The transition is carried out by randomly nucleating critical bubbles and the effects of thermal fluctuations (which could be relevant for vortex production) are represented by randomly nucleating subcritical bubbles. Our results show that the presence of subcritical bubbles suppresses vortices with clear and prominent profiles, though net number of vortices is consistent with theoretical estimates. We also determine the typical speed of vortices arising due to randomness associated with the phase transition to be about 0.5.