Signatures of the correlation hole in total and partial cross sections

In a complex scattering system with few open channels, say a quantum dot with leads, the correlation properties of the poles of the scattering matrix are most directly related to the internal dynamics of the system. We may ask how to extract these properties from an analysis of cross sections. In general this is very difficult, if we leave the domain of isolated resonances. We propose to consider the cross correlation function of two different elastic or total cross sections. For these we can show numerically and to some extent also analytically a significant dependence on the correlations between the scattering poles. The difference between uncorrelated and strongly correlated poles is clearly visible, even for strongly overlapping resonances.Comment: 25 pages, 13 Postscript figures, typos corrected and references adde

Optical-Model Description of Time-Reversal Violation

A time-reversal-violating spin-correlation coefficient in the total cross section for polarized neutrons incident on a tensor rank-2 polarized target is calculated by assuming a time-reversal-noninvariant, parity-conserving ``five-fold" interaction in the neutron-nucleus optical potential. Results are presented for the system $n + {^{165}{\rm Ho}}$ for neutron incident energies covering the range 1--20 MeV. From existing experimental bounds, a strength of $2 \pm 10$ keV is deduced for the real and imaginary parts of the five-fold term, which implies an upper bound of order $10^{-4}$ on the relative $T$-odd strength when compared to the central real optical potential.Comment: 11 pages (Revtex

Decay of Classical Chaotic Systems - the Case of the Bunimovich Stadium

The escape of an ensemble of particles from the Bunimovich stadium via a small hole has been studied numerically. The decay probability starts out exponentially but has an algebraic tail. The weight of the algebraic decay tends to zero for vanishing hole size. This behaviour is explained by the slow transport of the particles close to the marginally stable bouncing ball orbits. It is contrasted with the decay function of the corresponding quantum system.Comment: 16 pages, RevTex, 3 figures are available upon request from [email protected], to be published in Phys.Rev.

Waiting for the state: gender, citizenship and everyday encounters with bureaucracy in India

This article focuses on practices and meanings of time and waiting experienced by poor, low-class Dalits and Muslims in their routine encounters with the state in India. Drawing on ethnographic research from Tamil Nadu and Uttar Pradesh, it presents experiences of waiting around queuing and applying for paperwork, cards, and welfare schemes, in order to examine the role of temporal processes in the production of citizenship and citizen agency. An analysis of various forms of waiting – ‘on the day’, ‘to and fro’, and ‘chronic’ waiting – reveals how temporal processes operate as mechanisms of power and control through which state actors and other mediators produce differentiated forms of citizenship and citizens. Temporal processes and their material outcomes, we argue, are shaped by class, caste and religion, while also drawing on – and reproducing – gendered identities and inequalities. However, rather than being ‘passive’ patients of the state, we show how ordinary people draw on money, patronage networks and various performative acts in an attempt to secure their rights as citizens of India

The poetics of justice: aphorism and chorus as modes of anti-racism

This article revisits accounts of the black radical tradition as a critique and alternative to institutionalised modes of knowledge and learning, reprising Harney and Moten’s concept of the undercommons to think about the constraints of the university and the possibility for thinking differently together. The deployment of linguistic and conceptual difficulty as a tactic of political speech is linked to Sutherland’s discussion of Marx’s poetics, leading to the suggestion that the repetitive interspersing of poetic or theoretical fragments in the public speech of social justice actors operates to create a shared rhythm that establishes mutuality. The piece ends with a discussion of the refashioning of Audre Lorde as a voice punctuating the assertion of anti-racist and intersectional consciousness via social media

Molecular dynamics approach: from chaotic to statistical properties of compound nuclei

Statistical aspects of the dynamics of chaotic scattering in the classical model of $\alpha$-cluster nuclei are studied. It is found that the dynamics governed by hyperbolic instabilities which results in an exponential decay of the survival probability evolves to a limiting energy distribution whose density develops the Boltzmann form. The angular distribution of the corresponding decay products shows symmetry with respect to $\pi/2$ angle. Time estimated for the compound nucleus formation ranges within the order of $10^{-21}$s.Comment: 11 pages, LaTeX, non

Quantum mechanical time-delay matrix in chaotic scattering

We calculate the probability distribution of the matrix Q = -i \hbar S^{-1} dS/dE for a chaotic system with scattering matrix S at energy E. The eigenvalues \tau_j of Q are the so-called proper delay times, introduced by E. P. Wigner and F. T. Smith to describe the time-dependence of a scattering process. The distribution of the inverse delay times turns out to be given by the Laguerre ensemble from random-matrix theory.Comment: 4 pages, RevTeX; to appear in Phys. Rev. Let

Time-resolved dynamics of electron wave packets in chaotic and regular quantum billiards with leads

We perform numerical studies of the wave packet propagation through open quantum billiards whose classical counterparts exhibit regular and chaotic dynamics. We show that for t less or similar to tau (tau being the Heisenberg time), the features in the transmitted and reflected currents are directly related to specific classical trajectories connecting the billiard leads. In contrast, the long-time asymptotics of the wave packet dynamics is qualitatively different for classical and quantum billiards. In particularly, the decay of the quantum system obeys a power law that depends on the number of decay channels, and is not sensitive to the nature of classical dynamics (chaotic or regular).Comment: 5 pages, 4 figure