Wegner-Houghton equation in low dimensions

We consider scalar field theories in dimensions lower than four in the context of the Wegner-Houghton renormalization group equations (WHRG). The renormalized trajectory makes a non-perturbative interpolation between the ultraviolet and the infrared scaling regimes. Strong indication is found that in two dimensions and below the models with polynomial interaction are always non-perturbative in the infrared scaling regime. Finally we check that these results do not depend on the regularization and we develop a lattice version of the WHRG in two dimensions.Comment: 44 pages, 9 figures; some sections revised, refs. added; final version to appear in Phys. Rev.

Observers and their notion of spacetime beyond special relativity

It is plausible that quantum gravity effects may lead us to a description of Nature beyond the framework of special relativity. In this case, either the relativity principle is broken or it is maintained. These two scenarios (a violation or a deformation of special relativity) are very different, both conceptually and phenomenologically. We discuss some of their implications on the description of events for different observers and the notion of spacetime.Comment: 10 page

Microscopic systems with and without Coulomb interaction, fragmentation and phase transitions in finite nuclei

We test the influence of the Coulomb interaction on the thermodynamic and cluster generation properties of a system of classical particles described by different lattice models. Numerical simulations show that the Coulomb interaction produces essentially a shift in temperature of quantities like the specific heat but not qualitative changes. We also consider a cellular model. The thermodynamic properties of the system are qualitatively unaltered.Comment: 8 pages, 9 figures. New comments concerning the effect of the Coulomb interaction on the caloric curve. Justification of the criterion which defines bound clusters. Further comments about the identification of the order of the transition. To be published in Eur. Phys. J.

Beyond Special Relativity at second order

The study of generic, non-linear, deformations of Special Relativity parametrized by a high-energy scale $M$, which was carried out at first order in $M$ in Phys.Rev. D86, 084032 (2012), is extended to second order. This can be done systematically through a ('generalized') change of variables from momentum variables that transform linearly. We discuss the different perspectives on the meaning of the change of variables, obtain the coefficients of modified composition laws and Lorentz transformations at second order, and work out how $\kappa$-Poincar\'e, the most commonly used example in the literature, is reproduced as a particular case of the generic framework exposed here.Comment: 19 page

Spacetime from locality of interactions in deformations of special relativity: the example of κ\kappa-Poincar\'e Hopf algebra

A new proposal for the notion of spacetime in a relativistic generalization of special relativity based on a modification of the composition law of momenta is presented. Locality of interactions is the principle which defines the spacetime structure for a system of particles. The formulation based on $\kappa$-Poincar\'e Hopf algebra is shown to be contained in this framework as a particular example.Comment: 14 page