776 research outputs found
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 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 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
candidates with just background was
collected. The current status of the 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 ; the aim is to collect 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
- …