2,270 research outputs found
Decay of accelerated particles
We study how the decay properties of particles are changed by acceleration.
It is shown that under the influence of acceleration (1) the lifetime of
particles is modified and (2) new processes (like the decay of the proton)
become possible. This is illustrated by considering scalar models for the decay
of muons, pions, and protons. We discuss the close conceptual relation between
these processes and the Unruh effect.Comment: Latex2e, 12 pages, 6 Postscript figures included with epsfig, to
appear in Phys. Rev.
Aharonov-Bohm scattering of charged particles and neutral atoms: the role of absorption
The Aharonov-Bohm scattering of charged particles by the magnetic field of an
infinitely long and infinitely thin solenoid (magnetic string) in an absorbing
medium is studied. We discuss the partial-wave approach to this problem and
show that standard partial-wave method can be adjusted to this case. The effect
of absorption leads to oscillations of the AB cross section.
Based on this we investigate the scattering of neutral atoms with induced
electric dipole moments by a charge wire of finite radius which is placed in an
uniform magnetic field. The physical realistic and practically important case
that all atoms which collide with the wire are totally absorbed at its surface,
is studied in detail. The dominating terms of the scattering amplitude are
evaluated analytically for different physical constellations. The rest terms
are written in a form suitable for a numerical computation. We show that if the
magnetic field is absent, the absorbing charged wire causes oscillations of the
cross section. In the presence of the magnetic field the cross section
increases and the dominating Aharonov--Bohm peak appears in the forward
direction, suppressing the oscillations.Comment: 15 pages, LaTeXfile, 2 figure
Electron-positron pair production in the Aharonov-Bohm potential
In the framework of QED we evaluate the cross section for electron-positron
pair production by a single photon in the presence of the external
Aharonov-Bohm potential in first order of perturbation theory. We analyse
energy, angular and polarization distributions at different energy regimes:
near the threshold and at high photon energies.Comment: LaTeX file, 13 page
Zeno effect preventing Rabi transitions onto an unstable energy level
We consider a driven 2-level system with one level showing spontaneous decay
to an otherwise uncoupled third level. Rabi transitions to the unstable level
are strongly damped. This simple configuration can be used to demonstrate and
to explore the quantum Zeno effect leading to a freezing of the system to the
initial level. A comparison with repeated projection measurements is given. A
treatment within a phenomenological theory of continuous measurements is
sketched. The system visualizes the important role of null measurements
(negative result measurements) and may serve as a good example for a truly
continuous measurement.Comment: 13 pages, Latex, 2 EPS figure
Does Entrepreneurship Matter for Inclusive Growth? The Role of Social Progress Orientation
Building upon institutional economics, we examine how social progress orientation (SPO) affects inclusive growth through innovative and opportunity entrepreneurship. Hypotheses about civic activism, voluntary spirit, and the inclusion of minorities as proxies of SPO that affect entrepreneurship directly and inclusive growth indirectly have been suggested. Using unbalanced panel data of 132 observations (63 countries) and the three-stage least-squares method (3SLS), we provide empirical evidence that these three measures of SPO significantly affect innovative and opportunity entrepreneurship. Interestingly, our endogenous measures of entrepreneurial activity have served to explain inclusive growth, which is observed through poverty reduction across countries. Public policies should focus on social values oriented to progress in order to stimulate valuable entrepreneurial activity and hence facilitate economic development that also embraces vulnerable communities
Classical and quantum radiation from a moving charge in an expanding universe
We investigate photon emission from a moving particle in an expanding
universe. This process is analogous to the radiation from an accelerated charge
in the classical electromagnetic theory. Using the framework of quantum field
theory in curved spacetime, we demonstrate that the Wentzel-Kramers-Brillouin
(WKB) approximation leads to the Larmor formula for the rate of the radiation
energy from a moving charge in an expanding universe. Using exactly solvable
models in a radiation-dominated universe and in a Milne universe, we examine
the validity of the WKB formula. It is shown that the quantum effect suppresses
the radiation energy in comparison with the WKB formula.Comment: 16 pages, JCAP in pres
- …