Quasiparticle scattering and local density of states in graphite

We determine the effect of quasiparticle interference on the spatial variations of the local density of states (LDOS) in graphite in the neighborhood of an isolated impurity. A number of characteristic behaviors of interference are identified in the Fourier transformed spectrum. A comparison between our results and scanning tunneling microscopy (STM) experiments could provide a critical test of the range (of energy) of applicability of the Fermi liquid description of graphite, where some evidence of the breakdown of Fermi liquid theory has recently been discussed. Moreover, given the similarity between the band structures of graphite and that of nodal quasiparticles in a d-wave superconductor, a comparison between results in the two materials is useful for understanding the physics of the cuprates.Comment: 5 pages, 4 figures, RevTex

What Sways the Decision to Migrate? An Empirical Analysis of the Argentinean Case

Labour mobility among different regions within a country is known as one of the mechanisms that can contribute to the adjustment of regional labour markets. This will only occur on the condition that the individual’s responses to labour earnings differentials are sensitive enough. This paper provides with empirical evidence for Argentina concerning the analysis of the individual’s decision to migrate, and in particular, the response of the individuals to regional wage differentials, based on individual data. A random effects logit for panel data models the migration decision. The real expected income was found to signigficantly influence the probability of migrating.Migration Decision, Income, Random Effects Logit, Argentina

Emergent Higgsless Superconductivity

We present a new Higgsless model of superconductivity, inspired from anyon superconductivity but P- and T-invariant and generalizable to any dimension. While the original anyon superconductivity mechanism was based on incompressible quantum Hall fluids as average field states, our mechanism involves topological insulators as average field states. In D space dimensions it involves a (D-1)-form fictitious pseudovector gauge field which originates from the condensation of topological defects in compact low-energy effective BF theories. There is no massive Higgs scalar as there is no local order parameter. When electromagnetism is switched on, the photon acquires mass by the topological BF mechanism. Although the charge of the gapless mode (2) and the topological order (4) are the same as those of the standard Higgs model, the two models of superconductivity are clearly different since the origins of the gap, reflected in the high-energy sectors are totally different. In 2D this type of superconductivity is explicitly realized as global superconductivity in Josephson junction arrays. In 3D this model predicts a possible phase transition from topological insulators to Higgsless superconductors.Comment: Prepared for the proceedings of the XII Quark Confinement and the Hadron Spectrum, 29 August to 3 September 2016, Thessaloniki, Greece. arXiv admin note: substantial text overlap with arXiv:1408.506

Higgsless superconductivity from topological defects in compact BF terms

We present a new Higgsless model of superconductivity, inspired from anyon superconductivity but P- and T-invariant and generalizable to any dimension. While the original anyon superconductivity mechanism was based on incompressible quantum Hall fluids as average field states, our mechanism involves topological insulators as average field states. In D space dimensions it involves a (D-1)-form fictitious pseudovector gauge field which originates from the condensation of topological defects in compact low-energy effective BF theories. In the average field approximation, the corresponding uniform emergent charge creates a gap for the (D-2)-dimensional branes via the Magnus force, the dual of the Lorentz force. One particular combination of intrinsic and emergent charge fluctuations that leaves the total charge distribution invariant constitutes an isolated gapless mode leading to superfluidity. The remaining massive modes organise themselves into a D-dimensional charged, massive vector. There is no massive Higgs scalar as there is no local order parameter. When electromagnetism is switched on, the photon acquires mass by the topological BF mechanism. Although the charge of the gapless mode (2) and the topological order (4) are the same as those of the standard Higgs model, the two models of superconductivity are clearly different since the origins of the gap, reflected in the high-energy sectors are totally different. In 2D this type of superconductivity is explicitly realized as global superconductivity in Josephson junction arrays. In 3D this model predicts a possible phase transition from topological insulators to Higgsless superconductors.Comment: 12 pages, no figure

Strongly and Weakly Unstable Anisotropic Quark-Gluon Plasma

Using explicit solutions of the QCD transport equations, we construct an effective potential for an anisotropic quark-gluon plasma which under plausible assumptions holds beyond the Hard Loop approximation. The configurations, which are unstable in the linear response approach, are characterized by a negative quadratic term of the effective potential. The signs of higher order terms can be either negative or positive, depending on the parton momentum distribution. In the case of a Gaussian momentum distribution, the potential is negative and unbound from below. Therefore, the modes, which are unstable for gauge fields of small amplitude, remain unstable for arbitrary large amplitudes. We also present an example of a momentum distribution which gives a negative quadratic term of the effective potential but the whole potential has a minimum and it grows for sufficiently large gauge fields. Then, the system is weakly unstable. The character of the instability is important for the dynamical evolution of the plasma system.Comment: 13 pages, 1 figure, revised, to appear in Phys. Rev.

Political violence and economic growth

This paper analyzes the economic growth impact of organized political violence. First, the authors articulate the theoretical underpinnings of the growth impact of political violence in a popular model of growth under uncertainty. The authors show that, under plausible assumptions regarding attitudes toward risk, the overall effects of organized political violence are likely to be much higher than its direct capital destruction impact. Second, using a quantitative model of violence that distinguishes between three levels of political violence (riots, coups, and civil war), the authors use predicted probabilities of aggregate violence and its three manifestations to identify their growth effects in an encompassing growth model. Panel regressions suggest that organized political violence, especially civil war, significantly lowers long-term economic growth. Moreover, unlike most previous studies, the authors also find ethnic fractionalization to have a negative and direct effect on growth, though its effect is substantially ameliorated by the institutions specific to a non-factional partial democracy. Third, the results show that Sub-Saharan Africa has been disproportionately impacted by civil war, which explains a substantial share of its economic decline, including the widening income gap relative to East Asia. Civil wars have also been costly for Sub-Saharan Africa. For the case of Sudan, a typical large African country experiencing a long-duration conflict, the cost of war amounts to $46 billion (in 2000 fixed prices), whichis roughly double the country's current stock of external debt. Fourth, the authors suggest that to break free from its conflict-underdevelopment trap, Africa needs to better manage its ethnic diversity. The way to do this would be to develop inclusive, non-factional democracy. A democratic but factional polity would not work, and would be only marginally better than an authoritarian regime.Post Conflict Reconstruction,Population Policies,Hazard Risk Management,Post Conflict Reintegration,Social Conflict and Violence

Riots, coups and civil war : revisiting the greed and grievance debate

The most influential recent work on the determinants of civil wars found the factors associated with the grievance motivation to be largely irrelevant. Our paper subjects the results of this empirical work to further scrutiny by embedding the study of civil war in a more general analysis of varieties of violent contestation of political power within the borders of the state. Such an approach, we argue, will have important implications for how we think theoretically about the occurrence of domestic war as well as how we specify our empirical tests. In the empirical model, the manifestation of domestic conflict range from low intensity violence and coups to civil war. Our multinomial specification of domestic conflict supports the hypothesis that diversity accentuates distributional conflict and thus increases the risk of civil war. We also find that democracies may be more efficient than autocracies in reducing the risk of civil war.Post Conflict Reconstruction,Population Policies,Social Conflict and Violence,Peace&Peacekeeping,Hazard Risk Management