Quantum Dynamics in Non-equilibrium Strongly Correlated Environments

We consider a quantum point contact between two Luttinger liquids coupled to a mechanical system (oscillator). For non-vanishing bias, we find an effective oscillator temperature that depends on the Luttinger parameter. A generalized fluctuation-dissipation relation connects the decoherence and dissipation of the oscillator to the current-voltage characteristics of the device. Via a spectral representation, this result is generalized to arbitrary leads in a weak tunneling regime.Comment: 4 pages, 1 figur

New Upper Limits on the Tau Neutrino Mass from Primordial Helium Considerations

In this paper we reconsider recently derived bounds on $MeV$ tau neutrinos, taking into account previously unaccounted for effects. We find that, assuming that the neutrino life-time is longer than $O(100~sec)$, the constraint $N_{eff}<3.6$ rules out $\nu_{\tau}$ masses in the range $0.5~(MeV)<m_{\nu_\tau}<35~(MeV)$ for Majorana neutrinos and $0.74~(MeV)<m_{\nu_\tau}<35~(MeV)$ for Dirac neutrinos. Given that the present laboratory bound is 35 MeV, our results lower the present bound to $0.5$ and $0.74$ for Majorana and Dirac neutrinos respectively.Comment: 9 pages (2 figures available upon request), UM-AC-93-0

Fermion Chern Simons Theory of Hierarchical Fractional Quantum Hall States

We present an effective Chern-Simons theory for the bulk fully polarized fractional quantum Hall (FQH) hierarchical states constructed as daughters of general states of the Jain series, {\it i. e.} as FQH states of the quasi-particles or quasi-holes of Jain states. We discuss the stability of these new states and present two reasonable stability criteria. We discuss the theory of their edge states which follows naturally from this bulk theory. We construct the operators that create elementary excitations, and discuss the scaling behavior of the tunneling conductance in different situations. Under the assumption that the edge states of these fully polarized hierarchical states are unreconstructed and unresolved, we find that the differential conductance $G$ for tunneling of electrons from a Fermi liquid into {\em any} hierarchical Jain FQH states has the scaling behavior $G\sim V^\alpha$ with the universal exponent $\alpha=1/\nu$, where $\nu$ is the filling fraction of the hierarchical state. Finally, we explore alternative ways of constructing FQH states with the same filling fractions as partially polarized states, and conclude that this is not possible within our approach.Comment: 10 pages, 50 references, no figures; formerly known as "Composite Fermions: The Next Generation(s)" (title changed by the PRB thought police). This version has more references and a discussion of the stability of the new states. Published version. One erroneous reference is correcte

Edge reconstructions in fractional quantum Hall systems

Two dimensional electron systems exhibiting the fractional quantum Hall effects are characterized by a quantized Hall conductance and a dissipationless bulk. The transport in these systems occurs only at the edges where gapless excitations are present. We present a {\it microscopic} calculation of the edge states in the fractional quantum Hall systems at various filling factors using the extended Hamiltonian theory of the fractional quantum Hall effect. We find that at $\nu=1/3$ the quantum Hall edge undergoes a reconstruction as the background potential softens, whereas quantum Hall edges at higher filling factors, such as $\nu=2/5, 3/7$, are robust against reconstruction. We present the results for the dependence of the edge states on various system parameters such as temperature, functional form and range of electron-electron interactions, and the confining potential. Our results have implications for the tunneling experiments into the edge of a fractional quantum Hall system.Comment: 11 pages, 9 figures; minor typos corrected; added 2 reference

Edge reconstruction in the fractional quantum Hall regime

The interplay of electron-electron interaction and confining potential can lead to the reconstruction of fractional quantum Hall edges. We have performed exact diagonalization studies on microscopic models of fractional quantum Hall liquids, in finite size systems with disk geometry, and found numerical evidence of edge reconstruction under rather general conditions. In the present work we have taken into account effects like layer thickness and Landau level mixing, which are found to be of quantitative importance in edge physics. Due to edge reconstruction, additional nonchiral edge modes arise for both incompressible and compressible states. These additional modes couple to electromagnetic fields and thus can be detected in microwave conductivity measurements. They are also expected to affect the exponent of electron Green's function, which has been measured in tunneling experiments. We have studied in this work the electric dipole spectral function that is directly related to the microwave conductivity measurement. Our results are consistent with the enhanced microwave conductivity observed in experiments performed on samples with an array of antidots at low temperatures, and its suppression at higher temperatures. We also discuss the effects of the edge reconstruction on the single electron spectral function at the edge.Comment: 19 pages, 12 figure

Material-Specific Investigations of Correlated Electron Systems

We present the results of numerical studies for selected materials with strongly correlated electrons using a combination of the local-density approximation and dynamical mean-field theory (DMFT). For the solution of the DMFT equations a continuous-time quantum Monte-Carlo algorithm was employed. All simulations were performed on the supercomputer HLRB II at the Leibniz Rechenzentrum in Munich. Specifically we have analyzed the pressure induced metal-insulator transitions in Fe2O3 and NiS2, the charge susceptibility of the fluctuating-valence elemental metal Yb, and the spectral properties of a covalent band-insulator model which includes local electronic correlations.Comment: 14 pages, 7 figures, to appear in "High Performance Computing in Science and Engineering, Garching 2009" (Springer

Fractional-quantum-Hall edge electrons and Fermi statistics

We address the quantum statistics of electrons created in the low-energy edge-state Hilbert space sector of incompressible fractional quantum Hall states, considering the possibility that they may not satisfy Fermi statistics. We argue that this property is not a priori obvious, and present numerical evidence based on finite-size exact-diagonalization calculations that it does not hold in general. We discuss different possible forms for the expression for the electron creation operator in terms of edge boson fields and show that none are consistent with our numerical results on finite-size filling-factor-2/5 states with short-range electron-electron interactions. Finally, we discuss the current body of experimental results on tunneling into quantum Hall edges in the context of this result.Comment: 9 pages, 1 figure, RevTex

The fully differential single-top-quark cross section in next-to-leading order QCD

We present a new next-to-leading order calculation for fully differential single-top-quark final states. The calculation is performed using phase space slicing and dipole subtraction methods. The results of the methods are found to be in agreement. The dipole subtraction method calculation retains the full spin dependence of the final state particles. We show a few numerical results to illustrate the utility and consistency of the resulting computer implementations.Comment: 37 pages, latex, 2 ps figure

Revisiting the Higgs Mass and Dark Matter in the CMSSM

Taking into account the available accelerator and astrophysical constraints, the mass of the lightest neutral Higgs boson h in the minimal supersymmetric extension of the Standard Model with universal soft supersymmetry-breaking masses (CMSSM) has been estimated to lie between 114 and ~ 130 GeV. Recent data from ATLAS and CMS hint that m_h ~ 125 GeV, though m_h ~ 119 GeV may still be a possibility. Here we study the consequences for the parameters of the CMSSM and direct dark matter detection if the Higgs hint is confirmed, focusing on the strips in the (m_1/2, m_0) planes for different tan beta and A_0 where the relic density of the lightest neutralino chi falls within the range of the cosmological cold dark matter density allowed by WMAP and other experiments. We find that if m_h ~ 125 GeV focus-point strips would be disfavoured, as would the low-tan beta stau-chi and stop -chi coannihilation strips, whereas the stau-chi coannihilation strip at large tan beta and A_0 > 0 would be favoured, together with its extension to a funnel where rapid annihilation via direct-channel H/A poles dominates. On the other hand, if m_h ~ 119 GeV more options would be open. We give parametrizations of WMAP strips with large tan beta and fixed A_0/m_0 > 0 that include portions compatible with m_h = 125 GeV, and present predictions for spin-independent elastic dark matter scattering along these strips. These are generally low for models compatible with m_h = 125 GeV, whereas the XENON100 experiment already excludes some portions of strips where m_h is smaller.Comment: 24 pages, 9 figure