The intrinsic charge and spin conductivities of doped graphene in the Fermi-Liquid regime

The experimental availability of ultra-high-mobility samples of graphene opens the possibility to realize and study experimentally the "hydrodynamic" regime of the electron liquid. In this regime the rate of electron-electron collisions is extremely high and dominates over the electron-impurity and electron-phonon scattering rates, which are therefore neglected. The system is brought to a local quasi-equilibrium described by a set of smoothly varying (in space and time) functions, {\it i.e.} the density, the velocity field and the local temperature. In this paper we calculate the charge and spin conductivities of doped graphene due solely to electron-electron interactions. We show that, in spite of the linear low-energy band dispersion, graphene behaves in a wide range of temperatures as an effectively Galilean invariant system: the charge conductivity diverges in the limit $T \to 0$, while the spin conductivity remains finite. These results pave the way to the description of charge transport in graphene in terms of Navier-Stokes equations.Comment: 19 pages, 7 figures. arXiv admin note: text overlap with arXiv:1406.294

Calculi, Hodge operators and Laplacians on a quantum Hopf fibration

We describe Laplacian operators on the quantum group SUq (2) equipped with the four dimensional bicovariant differential calculus of Woronowicz as well as on the quantum homogeneous space S2q with the restricted left covariant three dimensional differential calculus. This is done by giving a family of Hodge dualities on both the exterior algebras of SUq (2) and S2q . We also study gauged Laplacian operators acting on sections of line bundles over the quantum sphere.Comment: v3, one reference corrected, one reference added. 31 page

The Incapacitation Effect of Incarceration: Evidence From Several Italian Collective Pardons

Incarceration of criminals reduces crime through two main channels, deterrence and incapac- itation. Because of a simultaneity between crime and incarceration–arrested criminals increase the prison population–it is difficult to measure these effects. This paper estimates the incapaci- tation effect on crime using a unique quasi-natural experiment, namely the recurrent collective pardoning between 1962 and 1995 of up to 35 percent of the Italian prison population. Since these pardons are enacted on a national level, unlike in Levitt (1996), we can control for the endogeneity of these laws that might be driven by criminals’ expectations: it is optimal to com- mit crimes shortly before a collective pardon gets enacted. This effect represents a deterrence effect, which, if not properly controlled for, would bias our IV estimates towards zero. The incapacitation effect is large and precisely estimated. The elasticity of crime with respect to prison population ranges, depending on the type of crime, between 0 and 49 percent. These numbers are increasing during our sample period, which suggests that habitual criminals are now more likely to be subject to pardons than in the past. A benefit-cost analysis suggests that pardons, seen as a short term solution to prison overcrowding, are inefficient.Crime, Pardon, Amnesty, Deterrence, Incapacitation

On the metastability of the Standard Model vacuum

If the Higgs mass m_H is as low as suggested by present experimental information, the Standard Model ground state might not be absolutely stable. We present a detailed analysis of the lower bounds on m_H imposed by the requirement that the electroweak vacuum be sufficiently long-lived. We perform a complete one-loop calculation of the tunnelling probability at zero temperature, and we improve it by means of two-loop renormalization-group equations. We find that, for m_H=115 GeV, the Higgs potential develops an instability below the Planck scale for m_t>(166\pm 2) GeV, but the electroweak vacuum is sufficiently long-lived for m_t < (175\pm 2) \GeV.Comment: LaTex 23 pages, 4 eps figures. Misprint in the abstract corrected, reference adde

Gauged Laplacians on quantum Hopf bundles

We study gauged Laplacian operators on line bundles on a quantum 2-dimensional sphere. Symmetry under the (co)-action of a quantum group allows for their complete diagonalization. These operators describe `excitations moving on the quantum sphere' in the field of a magnetic monopole. The energies are not invariant under the exchange monopole/antimonopole, that is under inverting the direction of the magnetic field. There are potential applications to models of quantum Hall effect.Comment: v2: latex; 32 pages. Papers re-organized; no major changes, several minor ones. Commun. Math. Phys. In pres

A linear approach for sparse coding by a two-layer neural network

Many approaches to transform classification problems from non-linear to linear by feature transformation have been recently presented in the literature. These notably include sparse coding methods and deep neural networks. However, many of these approaches require the repeated application of a learning process upon the presentation of unseen data input vectors, or else involve the use of large numbers of parameters and hyper-parameters, which must be chosen through cross-validation, thus increasing running time dramatically. In this paper, we propose and experimentally investigate a new approach for the purpose of overcoming limitations of both kinds. The proposed approach makes use of a linear auto-associative network (called SCNN) with just one hidden layer. The combination of this architecture with a specific error function to be minimized enables one to learn a linear encoder computing a sparse code which turns out to be as similar as possible to the sparse coding that one obtains by re-training the neural network. Importantly, the linearity of SCNN and the choice of the error function allow one to achieve reduced running time in the learning phase. The proposed architecture is evaluated on the basis of two standard machine learning tasks. Its performances are compared with those of recently proposed non-linear auto-associative neural networks. The overall results suggest that linear encoders can be profitably used to obtain sparse data representations in the context of machine learning problems, provided that an appropriate error function is used during the learning phase

Frequentist analyses of solar neutrino data (updated including KamLAND and SNO data)

The solar neutrino data are analyzed in a frequentist framework, using the Crow-Gardner and Feldman-Cousins prescriptions for the construction of confidence regions. Including in the fit only the total rates measured by the various experiments, both methods give results similar to the commonly used Delta chi^2-cut approximation. When fitting the full data set, the Delta chi^2-cut still gives a good approximation of the Feldman-Cousins regions. However, a careful statistical analysis significantly reduces the goodness-of-fit of the SMA and LOW solutions. In the addenda we discuss the implications of the latest KamLAND, SNO and SK data.Comment: 24 pages, 12 figures. Version 2: addendum about the CC SNO data (section 6). Version 3: addendum about the NC and day/night SNO data (section 7). Version 4: addendum about the KamLAND data (section 8). Version 5: addendum about SNO salt data (section 9, pages 22, 23). Version 6: final addendum about final SNO salt data and KamLAND (section 10, page 24

Hall viscosity and electromagnetic response of electrons in graphene

We derive an analytic expression for the geometric Hall viscosity of non-interacting electrons in a single graphene layer in the presence of a perpendicular magnetic field. We show that a recently-derived formula in [C. Hoyos and D. T. Son, Phys. Rev. Lett. {\bf 108}, 066805 (2012)], which connects the coefficient of $q^2$ in the wave vector expansion of the Hall conductivity $\sigma_{xy}(q)$ of the two-dimensional electron gas (2DEG) to the Hall viscosity and the orbital diamagnetic susceptibility of that system, continues to hold for graphene -- in spite of the lack of Galilean invariance -- with a suitable definition of the effective mass. We also show that, for a sufficiently large number of occupied Landau levels in the positive energy sector, the Hall conductivity of electrons in graphene reduces to that of a Galilean-invariant 2DEG with an effective mass given by $\hbar k_F/v_F$ (cyclotron mass). Even in the most demanding case, i.e. when the chemical potential falls between the zero-th and the first Landau level, the cyclotron mass formula gives results accurate to better than 1$\%$. The connection between the Hall conductivity and the viscosity provides a possible avenue to measure the Hall viscosity in graphene.Comment: 10 pages including one Appendix, one figure. As main modifications, in this version the result for the Hall viscosity and Hall conductivity of graphene reflect the expected electron-hole symmetry and a detailed discussion section has been added to compare our results with those obtained earlier in the literatur