Search results for "variance"
showing 10 items of 2030 documents
Improved description of the pion-nucleon scattering phenomenology in covariant baryon chiral perturbation theory
2014
We highlight some of the recent advances in the application of chiral effective field theory (chiral EFT) with baryons to the $\pi N$ scattering process. We recall some problems that cast doubt on the applicability of chiral EFT to $\pi N$ and show how the relativistic formalism, once the $\Delta(1232)$-resonance is included as an explicit degree of freedom, solves these issues. Finally it is shown how this approach can be used to extract the $\sigma$-terms from phenomenological information.
Relativistic Kinematics and Phase Space
2015
Here we present a list of the most important formulae needed for calculating relativistic collisions and decays. It includes one-to-two and one-to-three body decays, and the two-to-two scattering process both in the center of mass and laboratory frames. It also includes simplified general formulae of one, two and three-body Lorentz invariant phase space. No explicit calculation is performed, however the reader is highly encouraged to reproduce the results presented here.
A model of CPT violation for neutrinos
2002
Any local relativistic quantum field theory of Dirac-Weyl fermions conserves CPT. Here we examine whether a simple nonlocal field theory can violate CPT. We construct a new relativistic field theory of fermions, which we call ``homeotic'', which is nonlocal but causal and Lorentz invariant. The free homeotic theory is in fact equivalent to free Dirac theory. We show that a homeotic theory with a suitable nonlocal four-fermion interaction is causal and as a result has a well-defined perturbative S-matrix. By coupling a right-handed homeotic fermion to a left-handed Dirac-Weyl fermion, we obtain a causal theory of CPT-violating neutrino oscillations.
A fake Interacting Dark Energy detection?
2020
Models involving an interaction between the Dark Matter and the Dark Energy sectors have been proposed to alleviate the long standing Hubble constant tension. In this paper we analyze whether the constraints and potential hints obtained for these interacting models remain unchanged when using simulated Planck data. Interestingly, our simulations indicate that a dangerous fake detection for a non-zero interaction among the Dark Matter and the Dark Energy fluids could arise when dealing with current CMB Planck measurements alone. The very same hypothesis is tested against future CMB observations, finding that only cosmic variance limited polarization experiments, such as PICO or PRISM, could …
Charge and current distributions in elastic electron scattering by 1P shell nuclei
1974
The authors study the charge and magnetic form factors appearing in elastic electron scattering by 1p shell nuclei. The question that the form factors may be obtained from simple nuclear models by simply introducing a scaling factor has been examined using the j-j coupling, the L-S coupling and the intermediate coupling of Cohen-Kurath (CK) resulting from effective interactions. Results for /sup 6/Li, /sup 7 /Li, /sup 9/Be and /sup 13/C are given and the q/sup 2/ dependences of their form factors are compared in the three models and with experiment. The CK scheme gives similar results to the L-S coupling for /sup 6/Li and /sup 7/Li in agreement with experiment, whereas it is intermediate be…
Restrictions for asymmetry and polarizations of recoil in muon capture
1975
Abstract Using the helicity formalism, we discuss muon capture by targets of spin-zero. Owing to the definite neutrino helicity, three independent observables define a complete experiment. The precise relation between asymmetry α and longitudinal polarization P L of recoil, α = 1 + 2 jP L , comes only from rotational invariance. When time-reversal invariance is inserted, there is an additional restriction between the average polarization P av and the longitudinal polarization P L . On the basis of the experimental result P av = 0.43 ± 0.10 for 12 C, we predict P L = −(0.99 +0.01 −0.04 .
Unconstrained periodic boundary conditions for solid state elasticity
2004
We introduce a method to implement dynamics on an elastic lattice without imposing constraints via boundary or loading conditions. Using this method we are able to examine fracture processes in two-dimensional systems previously inaccessible for reliable computer simulations. We show the validity of the method by benchmarking and report a few preliminary results.
Is nuclear viscosity dependent on temperature?
2018
Nuclear viscosity is an indispensable ingredient of the nuclear fission collective dynamical models. It governs the exchange of energy between the collective variables and the thermal bath. Its dependence on the shape and temperature is a matter of controversy. By using systems of intermediate fissility we have demonstrated in a recent study that the viscosity parameters is larger for compact shapes, and decreases for larger deformations of the fissioning system, at variance with the conclusions of the statistical model modified to include empirically viscosity and time scales. In this contribution we propose an experimental scenario to highlight the possible dependence of the viscosity fro…
The Adiabatic Invariance of the Action Variables
2001
We shall first use an example to explain the concept of adiabatic invariance. Let us consider a “super ball” of mass m, which bounces back and forth between two walls (distance l) with velocity \(\boldsymbol{v}_{0}\). Let gravitation be neglected, and the collisions with the walls be elastic. If F m denotes the average force onto each wall, then we have $$\displaystyle{ F_{m}T = -\int _{\mathrm{coll.\,time}}f\,dt\;. }$$ (9.1) f is the force acting on the ball during one collision, and T is the time between collisions.
Reflection equations and q-Minkowski space algebras
1994
We express the defining relations of the $q$-deformed Minkowski space algebra as well as that of the corresponding derivatives and differentials in the form of reflection equations. This formulation encompasses the covariance properties with respect the quantum Lorentz group action in a straightforward way.