Recent results from Kaon Physics

A short review of recent results and future prospects in kaon physics is presented. Recent measurements performed at the NA48, NA62, KLOE and KTeV experiments on CP and Lepton Flavour violation and rare decays will be summarised, together with measurements of CKM elements and Chiral Perturbation Theory tests

Search for New Physics in NA62

The ratio $R_K=\frac{\Gamma(K\to e \nu_{e} (\gamma))}{\Gamma(K\to \mu \nu_{\mu} (\gamma))}$ of leptonic decay rates provides a golden probe for testing the structure of the weak interactions because it can be predicted with high accuracy within the Standard Model. The aim of the NA62 experimental programme based on the 2007 data set is a measurement of $R_K$ reaching a new accuracy level better than 0.4% \cite{evgueni}. To achieve this goal, data taking strategy allowing control over the systematic effects and in particular precise background subtraction, was worked out, and a data sample of $\sim0.16\times10^6$ $K_{e2}$ candidates with just $\sim10$ background was collected. The current status of the $K_{l2}$ analysis based on the dedicated NA62 data taking is summarized. The achieved precision of background subtraction, other systematic uncertainties, and prospects of the analysis are discussed. Within the same scientific programme, NA62, in its second phase, will measure the branching ratio of the very rare kaon decay $K^+ \to \pi^+ \nu \overline{\nu}$; the aim is to collect $\mathcal{O}(100)$ events with 10% background in two years data taking period. The status of the project, the R&D and future perspectives for the experimentComment: 4 page

A Quantum-Classical Model of Brain Dynamics

The study of the human psyche has elucidated a bipartite structure of cognition reflecting the quantum-classical nature of any process that generates knowledge and learning governed by brain activity. Acknowledging the importance of such a finding for modelization, we posit an approach to study brain by means of the quantum-classical dynamics of a Mixed Weyl symbol. The Mixed Weyl symbol is used to describe brain processes at the microscopic level and provides a link to the results of measurements made at the mesoscopic scale. Within this approach, quantum variables (such as,for example, nuclear and electron spins, dipole momenta of particles or molecules, tunneling degrees of freedom, etc may be represented by spinors while the electromagnetic fields and phonon modes involved in the processes are treated either classically or semi-classically, by also considering quantum zero-point fluctuations. Zero-point quantum effects can be incorporated into numerical simulations by controlling the temperature of each field mode via coupling to a dedicated Nos\`e-Hoover chain thermostat. The temperature of each thermostat is chosen in order to reproduce quantum statistics in the canonical ensemble. In this first paper, we introduce a quantum-classical model of brain dynamics, clarifying its mathematical strucure and focusing the discussion on its predictive value. Analytical consequences of the model are not reported in this paper, since they are left for future work. Our treatment incorporates compatible features of three well-known quantum approaches to brain dynamics - namely the electromagnetic field theory approach, the orchestrated objective reduction theory, and the dissipative quantum model of the brain - and hints at convincing arguments that sustain the existence of quantum-classical processes in the brain activity. All three models are reviewed.Comment: Submitted to Entropy [MDPI], Special Issue "Quantum Processes in Living Systems

New approach to describe two coupled spins in a variable magnetic field

We propose a method to describe the evolution of two spins coupled by hyperfine interaction in an external time-dependent magnetic field. We apply the approach to the case of hyperfine interaction with axial symmetry, which can be solved exactly in a constant, appropriately oriented magnetic field. In order to treat the nonstationary dynamical problem, we modify the time-dependent Schr\"odinger equation through a change of representation that, by exploiting an instantaneous (adiabatic) basis makes the time-dependent Hamiltonian diagonal at any time instant. The solution of the transformed time-dependent Schr\"odinger in the form of chronologically ordered exponents with transparent pre-exponential coefficients is reported. This solution is highly simplified when an adiabatically varying magnetic field perturbs the system. The approach here proposed may be used for the perturbative treatment of other dynamical problems with no exact solution