Chameleonic Theories: A Short Review

In the chameleon mechanism, a field (typically scalar) has a mass that depends on the matter density of the environment: the larger is the matter density, the larger is the mass of the chameleon. We briefly review some aspects of chameleonic theories. In particular, in a typical class of these theories, we discuss the lagrangian, the role of conformal transformations, the equation of motion and the thin-shell effect. We also discuss $f(R)$ theories and chameleonic quantum gravity.Comment: Invited contribution to the special issue "Modified Gravity Cosmology: from Inflation to Dark Energy", published in Universe. 30 pages. 2 figures. arXiv admin note: substantial text overlap with arXiv:hep-ph/0608078, arXiv:astro-ph/0611816 by other author

Measurement of the Higgs Boson Couplings and CP Structure Using Tau Leptons at the LHC

Results on the $H\to\tau\tau$ measurements performed by the ATLAS and CMS collaborations with the pp collision data collected at the LHC at $\sqrt{s}=$7 and 8 TeV are presented. These include a test of CP invariance in the VBF Higgs boson production. Experimental challenges for the test of the CP invariance in the $H\to\tau\tau$ decays are also reviewed.Comment: Presented at 14th International Workshop on Tau Lepton Physics (Tau2016

Chameleonic equivalence postulate and wave function collapse

A chameleonic solution to the cosmological constant problem and the non-equivalence of different conformal frames at the quantum level have been recently suggested [Phys. Rev. D82 (2010) 044006]. In this article we further discuss the theoretical grounds of that model and we are led to a chameleonic equivalence postulate (CEP). Whenever a theory satisfies our CEP (and some other additional conditions), a density-dependence of the mass of matter fields is naturally present. Let us summarize the main results of this paper. 1) The CEP can be considered the microscopic counterpart of the Einstein's Equivalence Principle and, hence, a chameleonic description of quantum gravity is obtained: in our model, (quantum) gravitation is equivalent to a conformal anomaly. 2) To illustrate one of the possible applications of the CEP, we point out a connection between chameleon fields and quantum-mechanical wave function collapse. The collapse is induced by the chameleonic nature of the theory. We discuss the collapse for a Stern-Gerlach experiment and for a diffraction experiment with electrons. More research efforts are necessary to verify whether these ideas are compatible with phenomenological constraints.Comment: 25 page