Species, chameleonic strings and the concept of particle

We recently proposed a chameleonic solution to the cosmological constant problem - Phys. Rev. D82 (2010) 044006. We further elaborate on our proposal discussing also some new results. The basic ingredients of the model are A) a chameleonic string dilaton parametrizing the amount of scale symmetry of the problem in the Einstein frame; B) a dual nature of the concept of particle where a splitting in local and global components is introduced (for every local particle a corresponding global particle is present in the theory). In this paper we proceed stepwise: 1) we point out that the value of the chameleonic dilaton in the Einstein frame parametrizes also the string length and, in particular, the string mass is an increasing function of the matter density; 2) the concept of global particle is clarified (indeed global particles are simply cosmic strings); 3) in the last quantization step, in the Feynman diagrams of our model, the UV cut-off (which is chosen to be the string mass) is a function of the chameleonic dilaton (naturally this stringy regularization is fully compatible with the chameleonic scale invariance of the model); 4) we show that a large number of particle species might be useful to keep locally under control the dangerous variations of the fundamental constants, however, more research efforts are necessary to make this point clear; 5) the chameleonic behaviour of matter fields and of the de Broglie wavelength of local matter particles is pointed out; 6) we briefly touch upon some ideas (which are still waiting for a full confirmation) regarding a potential connection between the shortest length scale of nature and the cosmological constant. A detailed phenomenological analysis of the entire model is required to test these ideas.