10,151 research outputs found
Energy-momentum tensor is nonsymmetric for spin-polarized photons
It has been assumed for a century that the energy-momentum tensor of the
photon takes a symmetric form, with the renowned Poynting vector assigned as
the same density for momentum and energy flow. Here we show that the symmetry
of the photon energy-momentum tensor can actually be inferred from the known
difference between the diffraction patterns of light with spin and orbital
angular momentum, respectively. The conclusion is that the symmetric expression
of energy-momentum tensor is denied, and the nonsymmetric canonical expression
is favored.Comment: 3 pages, 1 figur
Quantized electron transport by interference-induced quantum dots of two cross-travelling surface acoustic waves
In traditional approaches of obtaining quantized acoustoelectric current, a
narrow channel is fabricated to form quantum dots, which hold a fixed number of
electrons at a certain depth. We propose a natural way of forming quantum dots
without the narrow channel, by the interference of two surface acoustic waves
(SAWs) propagating across each other. A wide transportation area is defined by
the usual (but widely separated) split-gate structure with another independent
gate in between. This design can increase the quantized current by one to two
orders of magnitude. The three-gate structure also allows separate control of
the barrier height and the side-gate pinch-off voltage, thus avoids current
leakage through the area beneath the side gates.Comment: 2 pages, 3 figure
Co-existence of Gravity and Antigravity: The Unification of Dark Matter and Dark Energy
Massive gravity with second and fourth derivatives is shown to give both
attractive and repulsive gravities. In contrast to the attractive gravity
correlated with the energy-momentum tensor, the repulsive gravity is related to
a fixed mass , which equals a spin-dependent factor times the
graviton mass. Therefore, particles with energy below are both dark
matter and dark energy: Their overall gravity is attractive with normal matter
but repulsive among themselves. Detailed analyses reveal that this unified dark
scenario can properly account for the observed dark matter/energy phenomena:
galaxy rotation curves, transition from early cosmic deceleration to recent
acceleration; and naturally overcome other dark scenarios' difficulties: the
substructure and cuspy core problems, the difference of dark halo distributions
in galaxies and clusters, and the cosmic coincidence. Very interestingly, Dirac
particles have , all bosonic matter particles have
, and the only exceptional boson is the graviton itself, which may
have .Comment: 3 pages, no figure; discussions added that low-energy gravitons can
also serve as both dark matter and dark energy; references adde
Reverse the force direction at long distance by a running coupling
We reveal that a suitable running coupling can reverse the
direction of the one-particle-exchange (OPE) force at long distance if (and
under general assumptions, only if) the exchanged particle has a mass ,
either intrinsic or effective. The essential requirement on is an
extrapolating restriction . The running of can
be from either renormalization-group evolution or certain derivatives in the
Lagrangian. Reversal of the OPE force direction at long distance (namely,
attraction transits to repulsion, or vice versa) may have important
implications for gravity and cosmic acceleration, particle and nuclear physics,
and also condensed matter properties such as superconductivity.Comment: 6 pages, 2 figures; title changed, explicit example added with
referenc
Poincar\'e subalgebra and gauge invariance in nucleon structure
By separating the gluon field into physical and pure-gauge components, the
usual Poincar\'e subalgebra for an interacting system can be reconciled with
gauge-invariance when decomposing the total rotation and translation generators
of QCD into quark and gluon parts. The gauge-invariant quark/gluon parts act as
the generators for the gauge-invariant physical component of the quark/gluon
field, not the full quark/gluon field which also contains the gauge degrees of
freedom. We clarify that the naive canonical decomposition of generators, while
trivially respecting the Poincar\'e subalgebra, might not give a completely
gauge-invariant quark-gluon structure of the nucleon momentum and spin, though
limited invariance within a certain gauge class can be proven.Comment: 4 pages, no figure; presented at INT Workshop INT-12-49W "Orbital
Angular Momentum in QCD", Seattle, February 6-17, 201
Gauge invariance and hadron structure
We prove that the {\em gauge dependent} gluon spin, gluon and quark orbital
angular momenta operators have {\em gauge invariant} expectation values on
hadron states with {\em definite} momentum and polarization, therefore the
conventional decomposition of nucleon spin into contributions from the spin and
orbital angular momentum of quark and gluon is {\em gauge independent}. Similar
conclusions apply to the {\em gauge dependent} quark momentum and kinetic
energy operators, and accordingly nucleon momentum and mass structures.Comment: This revised version gives a complete, comprehensive proof of our
conclusion, and explains why the specific calculations of Hoodbhoy, Ji and Lu
(hep-ph/9808305) do not necessarily contradict our theore
Spin content of the nucleon in a valence and sea quark mixing model
A dynamical valence and sea quark mixing model is shown to fit the baryon
ground state properties as well as the spin content of the nucleon. The
relativistic correction and the transition
terms induced by the quark axial vector current
in this model space is responsible for the
quark spin reduction.Comment: 11 pages, Latex, one figure, to be published in Phys. Rev. C5
Some Problems in Defining Functional Integration over the Gauge Group
We find that sometimes the usual definition of functional integration over
the gauge group through limiting process may have internal difficulties.Comment: 2 pages revtex, no figur
A Note on Functional Integral over the Local Gauge Group
We evaluated some particular type of functional integral over the local gauge
group C^{\infty}({\bf R}^n, U(1)) by going to a discretized lattice. The
results explicitly violates the property of the Haar measure. We also analysed
the Faddeev-Popov method through a toy example. The results also violates the
property of the Haar measure.Comment: 7 pages, Revte
A Note on Invariant Measure on the Local Gauge Group
In this paper we investigated the problem of the existence of invariant
meaures on the local gauge group. We prove that it is impossible to define a
{\it finite} translationally invariant measure on the local gauge group
(where is an arbitrary matrix Lie group).Comment: 4 pages, REVTE
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