Compact lattice U(1) and Seiberg-Witten duality: a quantitative comparison

It was conjectured some time ago that an effective description of the Coulomb-confinement transition in compact U(1) lattice gauge field theory could be described by scalar QED obtained by soft breaking of the N=2 Seiberg-Witten model down to N=0 in the strong coupling region where monopoles are light. In two previous works this idea was presented at a qualitative level. In this work we analyze in detail the conjecture and obtain encouraging quantitative agreement with the numerical determination of the monopole mass and the dual photon mass in the vicinity of the Coulomb to confining phase transition.Comment: 14 pag, 5 figure

Axions and Cosmic Rays

We investigate the propagation of a charged particle in a spatially constant but time dependent pseudoscalar background. Physically this pseudoscalar background could be provided by a relic axion density. The background leads to an explicit breaking of Lorentz invariance; as a consequence processes such as $p\to p \gamma$ or $e\to e \gamma$ are possible within some kinematical constraints. The phenomenon is described by the QED lagrangian extended with a Chern-Simons term that contains a 4-vector which characterizes the breaking of Lorentz invariance induced by the time-dependent background. While the radiation induced (similar to the Cherenkov effect) is too small to influence the propagation of cosmic rays in a significant way, the hypothetical detection of the photons radiated by high energy cosmic rays via this mechanism would provide an indirect way of verifying the cosmological relevance of axions. We discuss on the order of magnitude of the effect.Comment: 16 pages, 3 figures. To appear in Proceedings of the Quarks 2010 International Seminar, Kolomna, Russi

Photon propagation in a cold axion condensate

We discuss some striking properties of photons propagating in a cold axion condensate oscillating coherently in time with a frequency $1/m_a$. Three effects are discussed in this contribution: (a) due to the time dependence of the background, photons moving in the cold axion background have no definite energies and some momenta are not accessible to them. (b) we investigate the combined influence of a magnetic field and the cold axion background and propose a possible interferometric experiment to detect the latter. (c) if the axion condensate has a space dependence, the photon refraction index is modified in the medium, possibly leading to total reflection at the interface with the ordinary vacuum.Comment: 6 pages, 4 figures, to appear in Proceedings of the Patras Workshop 2013, Mainz, June 201

Vector mesons in the Extended Chiral Quark Model

We extend our previous formulation of low-energy QCD in terms of an effective lagrangian containing operators of dimensionality $d\le 6$ constructed with pseudoscalars and quark fields, describing physics below the scale of chiral symmetry breaking. We include in this paper the vector and axial-vector channels. We follow closely the Extended Chiral Quark Model approach and consistently work in the large-$N_c$ and leading log approximation and take into account the constraints from chiral symmetry and chiral symmetry restoration. The optimal fit of all parameters gives further support to a heavy scalar meson with a mass $\sim 1$ GeV and a value of the axial pion-quark coupling constant $g_A \simeq 0.55$ to 0.66, depending on some assumptions concerning the Weinberg sum rules.Comment: 19 pages, Latex, JHEP class, more typos removed, few refs.adde

Pulsar Timing Arrays and the cosmological constant

In this talk I review how a non-zero cosmological constant $\Lambda$ affects the propagation of gravitational waves and their detection in pulsar timing arrays (PTA). If $\Lambda\neq 0$ it turns out that waves are anharmonic in cosmological Friedmann-Robertson- Walker coordinates and although the amount of anharmonicity is very small it leads to potentially measurable effects. The timing residuals induced by gravitational waves in PTA would show a peculiar angular dependence with a marked enhancement around a particular value of the angle subtended by the source and the pulsars. This angle depends mainly on the actual value of the cosmological constant and the distance to the source. Preliminary estimates indicate that the enhancement can be rather notorious for supermassive black hole mergers and in fact it could facilitate the first direct detection of gravitational waves while at the same time representing a `local' measurement of $\Lambda$.Comment: 13 pages, 7 figures (in 14 separate files), invited talk at the 2nd Russian-Spanish meeting on particle physics at all scales, Saint Petersburg (Russia), October 201

Spectrum of Relativistic Fermions in a 2d Doped Lattice

Motivated by some previous work on fermions on random lattices and by suggestions that impurities could trigger parity breaking in 2d crystals, we have analyzed the spectrum of the Dirac equation on a two dimensional square lattice where sites have been removed randomly --- a doped lattice. We have found that the system is well described by a sine-Gordon action. The solitons of this model are the lattice fermions, which pick a quartic interaction due to the doping and become Thirring fermions. They also get an effective mass different from the lagrangian mass. The system seems to exhibit spontaneous symmetry breaking, exactly as it happens for a randomly triangulated lattice. The associated ``Goldstone boson" is the sine-Gordon scalar. We argue, however, that the peculiar behaviour of the chiral condensate is due to finite size effects.Comment: 11 page