Possible Metal/Insulator Transition at B=0 in Two Dimensions

We have studied the zero magnetic field resistivity of unique high- mobility two-dimensional electron system in silicon. At very low electron density (but higher than some sample-dependent critical value, $n_{cr}\sim 10^{11}$ cm$^{-2}$), CONVENTIONAL WEAK LOCALIZATION IS OVERPOWERED BY A SHARP DROP OF RESISTIVITY BY AN ORDER OF MAGNITUDE with decreasing temperature below 1--2 K. No further evidence for electron localization is seen down to at least 20 mK. For $n_s<N_{cr}$, the sample is insulating. The resistivity is empirically found to SCALE WITH TEMPERATURE BOTH BELOW AND ABOVE $n_{cr}$ WITH A SINGLE PARAMETER which approaches zero at $n_s=n_{cr}$ suggesting a metal/ insulator phase transition.Comment: 10 pages; REVTeX v3.0; 3 POSTSCRIPT figures available upon request; to be published in PRB, Rapid Commu

Vacuum Fluctuations, Geometric Modular Action and Relativistic Quantum Information Theory

A summary of some lines of ideas leading to model-independent frameworks of relativistic quantum field theory is given. It is followed by a discussion of the Reeh-Schlieder theorem and geometric modular action of Tomita-Takesaki modular objects associated with the quantum field vacuum state and certain algebras of observables. The distillability concept, which is significant in specifying useful entanglement in quantum information theory, is discussed within the setting of general relativistic quantum field theory.Comment: 26 pages. Contribution for the Proceedings of a Conference on Special Relativity held at Potsdam, 200

Exponentiation of soft photons in a process involving hard photons

We present a simple method of removing the singularities associated with soft photon emission to all orders in perturbation theory through exponentiation, while keeping a consistent description of hard photon emission. We apply this method to the process e+ e- --> mu+ mu- + n photons where we include both Z^0 and photon exchange and retain the muon mass dependence. The photonic radiation is allowed to be radiated off any charged leg, and so we include all initial and final state radiation, as well as all interference effects. The effect of exponentiation is to suppress soft photon emission over the cross-section you would obtain from working at strictly leading order. We also show how one would extend the method to treat the collinear singularity; and remove the associated leading mass logarithms.Comment: 27 pages + 8 figures, plain TeX. Major changes from original submission. Available from ftp://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-833.ps.

Renal (Uremic) Encephalopathy in a Goat

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72407/1/j.1439-0442.2005.00752.x.pd

Heavy Higgs production and decay via e+e−→Z0H0→bbˉZ0Z0e^+e^-\to Z^0 H^0 \to b\bar bZ^0Z^0 and irreducible backgrounds at Next Linear Colliders

The complete matrix element for e^+e^-\ar b\bar bZ^0Z^0 has been computed at tree--level and applied to $Z^0H^0$--production followed by Z^0\ar b\bar b and H^0\ar Z^0Z^0, including all the irreducible background, at Next Linear Colliders. We find that, assuming flavour identification of the $Z^0$--decay products, this channel, together with e^+e^-\ar b\bar bW^+W^- in which Z^0H^0\ar (b\bar b)(W^+W^-), can be important for the study of the parameters of the Standard Model Higgs boson over the heavy mass range 2M_{Z^0}\Ord M_{H^0}\Ord 2{m_t}.Comment: 24 pages, LaTeX (uses Feynman), 7 figures (.ps files or hardcopies of figs.2-7 available upon request

Investigation of EMIC wave scattering as the cause for the BARREL 17 January 2013 relativistic electron precipitation event: A quantitative comparison of simulation with observations

Abstract Electromagnetic ion cyclotron (EMIC) waves were observed at multiple observatory locations for several hours on 17 January 2013. During the wave activity period, a duskside relativistic electron precipitation (REP) event was observed by one of the Balloon Array for Radiation belt Relativistic Electron Losses (BARREL) balloons and was magnetically mapped close to Geostationary Operational Environmental Satellite (GOES) 13. We simulate the relativistic electron pitch angle diffusion caused by gyroresonant interactions with EMIC waves using wave and particle data measured by multiple instruments on board GOES 13 and the Van Allen Probes. We show that the count rate, the energy distribution, and the time variation of the simulated precipitation all agree very well with the balloon observations, suggesting that EMIC wave scattering was likely the cause for the precipitation event. The event reported here is the first balloon REP event with closely conjugate EMIC wave observations, and our study employs the most detailed quantitative analysis on the link of EMIC waves with observed REP to date. Key PointsQuantitative analysis of the first balloon REP with closely conjugate EMIC wavesOur simulation suggests EMIC waves to be a viable cause for the REP eventThe adopted model is proved to be applicable to simulating the REP event

Search for the Flavor-Changing Neutral-Current Decays D+→π+μ+μ−D^+\to \pi^+ \mu^+ \mu^- and D+→π+e+e−D^+\to \pi^+ e^+ e^-

We report the results of a search for the flavor-changing neutral-current decays $D^+\rightarrow \pi^+ \mu^+ \mu^-$ and $D^+\rightarrow \pi^+ e^+ e^-$ in data from Fermilab charm hadroproduction experiment E791. No signal above background is found, and we obtain upper limits on branching fractions, $B(D^+\rightarrow \pi^+ \mu^+ \mu^-) < 1.8 \times 10^{-5}$ and $B(D^+\rightarrow \pi^+ e^+ e^-) < 6.6 \times 10^{-5}$, at the 90\% confidence level.Comment: nine pages with figures; compressed, uuencoded postscrip

Financial Transaction Tax: Small is Beautiful

The case for taxing financial transactions merely to raise more revenues from the financial sector is not particularly strong. Better alternatives to tax the financial sector are likely to be available. However, a tax on financial transactions could be justified in order to limit socially undesirable transactions when more direct means of doing so are unavailable for political or practical reasons. Some financial transactions are indeed likely to do more harm than good, especially when they contribute to the systemic risk of the financial system. However, such a financial transaction tax should be very small, much smaller than the negative externalities in question, because it is a blunt instrument that also drives out socially useful transactions. There is a case for taxing over-the-counter derivative transactions at a somewhat higher rate than exchange-based derivative transactions. More targeted remedies to drive out socially undesirable transactions should be sought in parallel, which would allow, after their implementation, to reduce or even phase out financialtransaction taxes

Local covariant quantum field theory over spectral geometries

A framework which combines ideas from Connes' noncommutative geometry, or spectral geometry, with recent ideas on generally covariant quantum field theory, is proposed in the present work. A certain type of spectral geometries modelling (possibly noncommutative) globally hyperbolic spacetimes is introduced in terms of so-called globally hyperbolic spectral triples. The concept is further generalized to a category of globally hyperbolic spectral geometries whose morphisms describe the generalization of isometric embeddings. Then a local generally covariant quantum field theory is introduced as a covariant functor between such a category of globally hyperbolic spectral geometries and the category of involutive algebras (or *-algebras). Thus, a local covariant quantum field theory over spectral geometries assigns quantum fields not just to a single noncommutative geometry (or noncommutative spacetime), but simultaneously to ``all'' spectral geometries, while respecting the covariance principle demanding that quantum field theories over isomorphic spectral geometries should also be isomorphic. It is suggested that in a quantum theory of gravity a particular class of globally hyperbolic spectral geometries is selected through a dynamical coupling of geometry and matter compatible with the covariance principle.Comment: 21 pages, 2 figure

Unpaired and spin-singlet paired states of a two-dimensional electron gas in a perpendicular magnetic field

We present a variational study of both unpaired and spin-singlet paired states induced in a two-dimensional electron gas at low density by a perpendicular magnetic field. It is based on an improved circular-cell approximation which leads to a number of closed analytical results. The ground-state energy of the Wigner crystal containing a single electron per cell in the lowest Landau level is obtained as a function of the filling factor $\nu$: the results are in good agreement with those of earlier approaches and predict $\nu_{c} \approx 0.25$ for the upper filling factor at which the solid-liquid transition occurs. A novel localized state of spin-singlet electron pairs is examined and found to be a competitor of the unpaired state for filling factor $\nu >1$. The corresponding phase boundary is quantitatively displayed in the magnetic field-electron density plane.Comment: 19 pages, 8 figures, submitted to Phys. Rev. B on 7th April 2001. to appear in Phys. Rev.