Search results for "Energy–momentum relation"
showing 10 items of 18 documents
Laser-induced collective excitations in a two-component Fermi gas
2002
We consider the linear density response of a two-component (superfluid) Fermi gas of atoms when the perturbation is caused by laser light. We show that various types of laser excitation schemes can be transformed into linear density perturbations, however, a Bragg spectroscopy scheme is needed for transferring energy and momentum into a collective mode. This makes other types of laser probing schemes insensitive for collective excitations and therefore well suited for the detection of the superfluid order parameter. We show that for the special case when laser light is coupled between the two components of the Fermi gas, density response is always absent in a homogeneous system.
Renormalization group improved gravitational actions: A Brans-Dicke approach
2003
A new framework for exploiting information about the renormalization group (RG) behavior of gravity in a dynamical context is discussed. The Einstein-Hilbert action is RG-improved by replacing Newton's constant and the cosmological constant by scalar functions in the corresponding Lagrangian density. The position dependence of $G$ and $\Lambda$ is governed by a RG equation together with an appropriate identification of RG scales with points in spacetime. The dynamics of the fields $G$ and $\Lambda$ does not admit a Lagrangian description in general. Within the Lagrangian formalism for the gravitational field they have the status of externally prescribed ``background'' fields. The metric sat…
Nonlocalities and Fermi motion corrections in K- atoms
2002
We evaluate the p-wave $K^-N$ amplitudes from the chiral Lagrangians and from there construct the p-wave part of the $K^-$ nucleus optical potential plus a small s-wave part induced from the elementary p-wave amplitude and the nuclear Fermi motion. Simultaneously, the momentum and energy dependence of the s-wave optical potential, previously developed, are taken into account and shown to generate a small p-wave correction to the optical potential. All the corrections considered are small compared to the leading s-wave potential, and lead to changes in the shifts and widths which are smaller than the experimental errors. A thorough study of the threshold region and low densities is conducted…
The MAMI-project
2008
In the energy region up to one GeV the "racetrack"-microtron /1/ offers an economic way to achieve a 100% duty factor e--beam with a high current (IO0~A) and a well defined energy (Ap/p ~ 10-4). Such an e--beam appears to be ideal for the experimental investigation of the nucleus: coincidence experiments of the type (e,e'x) and (e,e'xy) become possible in a wide kinematical region yielding information about the response of the nucleus to the transferred energy and momentum. By the method of bremsstrahl-tagging, for the f i r s t time, rather intensive ( few times 107/sec) photon beams with high monochromaticity and well known fluxes wi l l be available. To make the best use out of such new …
Quasi-deuteron effects at intermediate energies
2008
It has been shown that photon and pion reactions in certain energy regions are dominated by the absorption on correlated (n-p)-pairs. Therefore, calculations based on quasi-deuteron models describe rather well the present experimental results. However, with more accurate data out of the reactions (γ,np),(γ,N), (π,NN) and (π,N) performed so that the complete kinematics is known, the correlation function of nucleon pairs in nuclei can be studied a quantity very important for our understanding of the nuclear many body system. The dominance for absorption on pairs in reactions with a rather big mismatch in energy and momentum in the entrance channel compared with the exit channel of the reactio…
Flux expressions and NEMD perturbations for models of semi-flexible molecules
2001
We derive energy and momentum flux expressions, for systems composed of a general class of semi-flexible molecules, in the Ciccotti-Ferrario-Ryckaert linear constraint formalism. According to this formalism, the whole set of Cartesian coordinates is divided into basic (independent) and secondary (dependent) subsets. It is found that energy and momentum flux vectors have a simple and general expression using both basic and secondary coordinates. In the case of non-equilibrium molecular dynamics, we give general and simple heat and shear flow algorithms, deriving the dissipative fluxes in the space of all Cartesian coordinates. In comparison with previous derivations for some models of flexib…
Thermalization of the dispersive three-wave interaction
2007
We investigate the role of dispersion effects on the long-term evolution of the nonlinear three-wave interaction. We show that the three waves exhibit, as a general rule, an irreversible evolution towards a thermodynamic equilibrium state in which they propagate with identical velocities. As a result of this thermalization process, the three-wave system is driven away from spatio-temporal resonance, so that the equilibrium state does not satisfy the (phase-matching) resonant conditions of energy and momentum conservation for the averaged frequencies. Moreover, we show that the interplay between temporal dispersion and spatial diffraction leads to the emergence of a peculiar equilibrium stat…
Two-nucleon mechanism for antiproton annihilation in nuclei
1986
Abstract The annihilation probability of an antiproton inside a nucleus is evaluated via the p NN → N n π reaction. For that purpose the p N→( n +1)π reaction is started from and one of the pions is allowed to be virtual, carrying the appropriate energy and momentum to produce physical particle-hole excitations. The new mechanism proves to be very important: at nuclear densities around ϱ = 0.2 ϱ 0 it has about the same strength as the one-nucleon annihilation mechanism, and becomes much more important as the nuclear density increases. The repercussion of the new channel in the p -nucleus annihilation cross section is studied and its relevance in p atoms and p -nucleus elastic scattering is …
Morphology and Dynamics of Relativistic Jets
1997
We present a comprehensive analysis of the morphology and dynamics of relativistic pressure-matched axisymmetric jets. The numerical simulations have been carried out with a high-resolution shock-capturing hydrocode based on an approximate relativistic Riemann solver derived from the spectral decomposition of the Jacobian matrices of relativistic hydrodynamics. We discuss the dependence of the jet morphology on several parameters, paying special attention to the relativistic effects caused by high Lorentz factors and large internal energies of the beam flow. The parameter space of our analysis is spanned by the ratio of the beam and ambient medium rest mass density (η), the beam Mach number…
Superdeformations in Relativistic and Non-Relativistic Mean Field Theories
1999
The applications of the extensions of relativistic mean field (RMF) theory to the rotating frame, such as cranked relativistic mean field (CRMF) theory and cranked relativistic Hartree-Bogoliubov (CRHB) theory, for the description of superdeformed bands in the $A\sim 60$, 140-150 and 190 mass regions are overviewed and compared briefly with the results obtained in non-relativistic mean field theories.