281 research outputs found
On the non-vanishing of the Collins mechanism for single spin asymmetries
The Collins mechanism provides a non-perturbative explanation for the large
single spin asymmetries found in hard semi-inclusive reactions involving a
transversely polarized nucleon. However, there are seemingly convincing reasons
to suspect that the mechanism vanishes, and indeed it does vanish in the naive
parton model where a quark is regarded as an essentially 'free' particle. We
give an intuitive analysis which highlights the difference between the naive
picture and the realistic one, and shows how the Collins mechanism arises when
the quark is described as an off-shell particle by a field in interaction. A
typographical error is corrected in this version.Comment: 15 pages, 2 figure
Ringing the Randall-Sundrum braneworld: metastable gravity wave bound states
In the Randall-Sundrum scenario, our universe is a 4-dimensional `brane'
living in a 5-dimensional bulk spacetime. By studying the scattering of bulk
gravity waves, we show that this brane rings with a characteristic set of
complex quasinormal frequencies, much like a black hole. To a bulk observer
these modes are interpreted as metastable gravity wave bound states, while a
brane observer views them as a discrete spectrum of decaying massive gravitons.
Potential implications of these scattering resonances are discussed.Comment: References and misc. comments added. "Implications" section expanded.
REVTeX4, 5 pages, 4 figure
General U(N) gauge transformations in the realm of covariant Hamiltonian field theory
A consistent, local coordinate formulation of covariant Hamiltonian field
theory is presented. While the covariant canonical field equations are
equivalent to the Euler-Lagrange field equations, the covariant canonical
transformation theory offers more general means for defining mappings that
preserve the action functional - and hence the form of the field equations -
than the usual Lagrangian description. Similar to the well-known canonical
transformation theory of point dynamics, the canonical transformation rules for
fields are derived from generating functions. As an interesting example, we
work out the generating function of type F_2 of a general local U(N) gauge
transformation and thus derive the most general form of a Hamiltonian density
that is form-invariant under local U(N) gauge transformations.Comment: 36 pages, Symposium on Exciting Physics: Quarks and gluons/atomic
nuclei/biological systems/networks, Makutsi Safari Farm, South Africa, 13-20
November 2011; Exciting Interdisciplinary Physics, Walter Greiner, Ed., FIAS
Interdisciplinary Science Series, Springer International Publishing
Switzerland, 201
Baryon Fields with U_L(3) \times U_R(3) Chiral Symmetry: Axial Currents of Nucleons and Hyperons
We use the conventional F and D octet and decimet generator matrices to
reformulate chiral properties of local (non-derivative) and one-derivative
non-local fields of baryons consisting of three quarks with flavor SU(3)
symmetry that were expressed in SU(3) tensor form in Ref. [12]. We show
explicitly the chiral transformations of the [(6,3)\oplus(3,6)] chiral
multiplet in the "SU(3) particle basis", for the first time to our knowledge,
as well as those of the (3,\bar{3}) \oplus (\bar{3}, 3), (8,1) \oplus (1,8)
multiplets, which have been recorded before in Refs. [4,5]. We derive the
vector and axial-vector Noether currents, and show explicitly that their zeroth
(charge-like) components close the SU_L(3) \times SU_R(3) chiral algebra. We
use these results to study the effects of mixing of (three-quark) chiral
multiplets on the axial current matrix elements of hyperons and nucleons. We
show, in particular, that there is a strong correlation, indeed a definite
relation between the flavor-singlet (i.e. the zeroth), the isovector (the
third) and the eighth flavor component of the axial current, which is in decent
agreement with the measured ones.Comment: one typo correction, and accepted by PR
Spherically symmetric spacetimes in f(R) gravity theories
We study both analytically and numerically the gravitational fields of stars
in f(R) gravity theories. We derive the generalized Tolman-Oppenheimer-Volkov
equations for these theories and show that in metric f(R) models the
Parameterized Post-Newtonian parameter is a robust
outcome for a large class of boundary conditions set at the center of the star.
This result is also unchanged by introduction of dark matter in the Solar
System. We find also a class of solutions with in
the metric model, but these solutions turn out to be unstable
and decay in time. On the other hand, the Palatini version of the theory is
found to satisfy the Solar System constraints. We also consider compact stars
in the Palatini formalism, and show that these models are not inconsistent with
polytropic equations of state. Finally, we comment on the equivalence between
f(R) gravity and scalar-tensor theories and show that many interesting Palatini
f(R) gravity models can not be understood as a limiting case of a
Jordan-Brans-Dicke theory with .Comment: Published version, 12 pages, 7 figure
WKB approximation for multi-channel barrier penetrability
Using a method of local transmission matrix, we generalize the well-known WKB
formula for a barrier penetrability to multi-channel systems. We compare the
WKB penetrability with a solution of the coupled-channels equations, and show
that the WKB formula works well at energies well below the lowest adiabatic
barrier. We also discuss the eigen-channel approach to a multi-channel
tunneling, which may improve the performance of the WKB formula near and above
the barrier.Comment: 15 pages, 4 eps figure
Wave Mechanics of a Two Wire Atomic Beamsplitter
We consider the problem of an atomic beam propagating quantum mechanically
through an atom beam splitter. Casting the problem in an adiabatic
representation (in the spirit of the Born-Oppenheimer approximation in
molecular physics) sheds light on explicit effects due to non-adiabatic passage
of the atoms through the splitter region. We are thus able to probe the fully
three dimensional structure of the beam splitter, gathering quantitative
information about mode-mixing, splitting ratios,and reflection and transmission
probabilities
A comparative study of some models of incoherence at the mesoscopic scale
The pre-existing literature on phenomena at the mesoscopic scale is concerned
among other things with phase coherent transport. Phase coherent transport
dominates at very low temperatures. With increase in temperature, as the system
size becomes comparable to the inelastic mean free path phase incoherence sets
in. This incoherence further leads to dephasing, and as a consequence purely
quantum effects in electron transport give way to classical macroscopic
behavior. In this work we consider two distinct phenomenological models of
incoherent transport, the Coherent Absorption and Wave Attenuation models. We
reveal some physical problems in the Coherent Absorption model as opposed to
the Wave Attenuation model. We also compare our proposed model with experiments
in case of the much studied peak to valley ratios in resonant tunneling diodes,
magneto-conductance oscillations and Fano resonances in case of Aharonov-Bohm
rings.Comment: 20 pages, 9 figure
Time-dependent approach to many-particle tunneling in one-dimension
Employing the time-dependent approach, we investigate a quantum tunneling
decay of many-particle systems. We apply it to a one-dimensional three-body
problem with a heavy core nucleus and two valence protons. We calculate the
decay width for two-proton emission from the survival probability, which well
obeys the exponential decay-law after a sufficient time. The effect of the
correlation between the two emitted protons is also studied by observing the
time evolution of the two-particle density distribution. It is shown that the
pairing correlation significantly enhances the probability for the simultaneous
diproton decay.Comment: 9 pages, 10 eps figure
Covariant Hamiltonian Field Theory
A consistent, local coordinate formulation of covariant Hamiltonian field
theory is presented. Whereas the covariant canonical field equations are
equivalent to the Euler-Lagrange field equations, the covariant canonical
transformation theory offers more general means for defining mappings that
preserve the form of the field equations than the usual Lagrangian description.
It is proved that Poisson brackets, Lagrange brackets, and canonical 2-forms
exist that are invariant under canonical transformations of the fields. The
technique to derive transformation rules for the fields from generating
functions is demonstrated by means of various examples. In particular, it is
shown that the infinitesimal canonical transformation furnishes the most
general form of Noether's theorem. We furthermore specify the generating
function of an infinitesimal space-time step that conforms to the field
equations.Comment: 93 pages, no figure
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