Condensates beyond the horizons

In this work we continue our previous studies concerning the possibility of the existence of a Bose-Einstein condensate in the interior of a static black hole, a possibility first advocated by Dvali and G\'omez. We find that the phenomenon seems to be rather generic and it is associated to the presence of an horizon, acting as a confining potential. We extend the previous considerations to a Reissner-Nordstr\"om black hole and to the de Sitter cosmological horizon. In the latter case the use of static coordinates is essential to understand the physical picture. In order to see whether a BEC is preferred, we use the Brown-York quasilocal energy, finding that a condensate is energetically favourable in all cases in the classically forbidden region. The Brown-York quasilocal energy also allows us to derive a quasilocal potential, whose consequences we explore. Assuming the validity of this quasilocal potential allows us to suggest a possible mechanism to generate a graviton condensate in black holes. However, this mechanism appears not to be feasible in order to generate a quantum condensate behind the cosmological de Sitter horizon.Comment: 25 pages, 6 figure

The emergence of geometry: a two-dimensional toy model

We review the similarities between the effective chiral lagrangrian, relevant for low-energy strong interactions, and the Einstein-Hilbert action. We use these analogies to suggest a specific mechanism whereby gravitons would emerge as Goldstone bosons of a global SO(D) X GL(D) symmetry broken down to SO(D) by fermion condensation. We propose a two-dimensional toy model where a dynamical zwei-bein is generated from a topological theory without any pre-existing metric structure, the space being endowed only with an affine connection. A metric appears only after the symmetry breaking; thus the notion of distance is an induced effective one. In spite of several non-standard features this simple toy model appears to be renormalizable and at long distances is described by an effective lagrangian that corresponds to that of two-dimensional gravity (Liouville theory). The induced cosmological constant is related to the dynamical mass M acquired by the fermion fields in the breaking, which also acts as an infrared regulator. The low-energy expansion is valid for momenta k >M, i.e. for supra-horizon scales. We briefly discuss a possible implementation of a similar mechanism in four dimensions.Comment: 18 page

How a cold axion background influences photons

A cold relic axion condensate resulting from vacuum misalignment in the early universe oscillates with a frequency \sim m_a, where m_a is the axion mass. We summarize how the properties of photons propagating in such a medium are modified. Although the effects are small due to the magnitude of the axion-photon coupling, some consequences are striking.Comment: 4 pages, 4 figures. To appear in "Proceedings of the 7th Patras Workshop on Axions, WIMPs and WISPs

Compact lattice U(1) and Seiberg-Witten duality

Simulations in compact U(1) lattice gauge theory in 4D show now beyond any reasonable doubts that the phase transition separating the Coulomb from the confined phase is of first order, albeit a very weak one. This settles the issue from the numerical side. On the analytical side, it was suggested some time ago, based on the qualitative analogy between the phase diagram of such a model and the one of scalar QED obtained by soft breaking the N=2 Seiberg-Witten model down to N=0, that the phase transition should be of second order. In this work we take a fresh look at this issue and show that a proper implementation of the Seiberg-Witten model below the supersymmetry breaking scale requires considering some new radiative corrections. Through the Coleman-Weinberg mechanism this turns the second order transition into a weakly first order one, in agreement with the numerical results. We comment on several other aspects of this continuum model.Comment: 15 pages 4 figure

Algunes qüestions de renormalització a la cromodinàmica quàntica

[cat] Sembla obligat començar fent referència a les raons teòriques i experimentals que ens fan creure en la Cromodinàmica Quàntica com en la Teoria de Camps adient a la descripció del mon hadrònic. Per a creure en una teoria necessitem, seguint Wightman, dos requisits: ha d'estar lliure de contradiccions i ha de satisfer un rang més o menys ampli d'observacions experimentals. És en aquest sentit que hom creu en les equacions de Maxwelll, però no ho fa en l’antiga teoria quàntica anterior a la Mecànica Ondulatòria. En els dos aspectes la resposta ha d'ésser matisada.Pel que coneixem fins aquest moment QCD és una teoria lliure d'inconsistències internes, al menys a un nivell molt fonamental. És una teoria de gauge -i creiem en les teories de gauge per a l'explicació de totes les interaccions- convenientment definida (en un sentit ampli del terme), renormalitzable i unitària. A grans trets, el problema que ens impedeix donar una resposta conclusiva és la probable inexistència de la matriu S almenys en un sentit pertorbatiu