33,101 research outputs found
Resolution of the strong CP and U(1) problems
Definition of the determinant of Euclidean Dirac operator in the nontrivial
sector of gauge fields suffers from an inherent ambiguity. The popular
Osterwalder-Schrader (OS) recipe for the conjugate Dirac field leads to the
option of a vanishing determinant. We propose a novel representation for the
conjugate field which depends linearly on the Dirac field and yields a
nonvanishing determinant in the nontrivial sector. Physics, it appears, chooses
this second option becuase the novel representation leads to a satisfactory
resolution of two outstanding problems, the strong CP and U(1) problems,
attributed to instanton effects.Comment: Latex file, 9 pages, no figur
Is there still a strong CP problem?
The role of a chiral U(1) phase in the quark mass in QCD is analysed from
first principles. In operator formulation, there is a parity symmetry and the
phase can be removed by a change in the representation of the Dirac gamma
matrices. Moreover, these properties are also realized in a Pauli-Villars
regularized version of the theory. In the functional integral scenario,
attempts to remove the chiral phase by a chiral transformation are thought to
be obstructed by a nontrivial Jacobian arising from the fermion measure and the
chiral phase may therefore seem to break parity. But if one starts from the
regularized action with the chiral phase also present in the regulator mass
term, the Jacobian for a combined chiral rotation of quarks and regulators is
seen to be trivial and the phase can be removed by a combined chiral rotation.
This amounts to a taming of the strong CP problem.Comment: 6 pages, REVTeX; brief discussion available at
http://theory.saha.ernet.in/~mitra/scp.htm
A Canonical Approach to the Quantization of the Damped Harmonic Oscillator
We provide a new canonical approach for studying the quantum mechanical
damped harmonic oscillator based on the doubling of degrees of freedom
approach. Explicit expressions for Lagrangians of the elementary modes of the
problem, characterising both forward and backward time propagations are given.
A Hamiltonian analysis, showing the equivalence with the Lagrangian approach,
is also done. Based on this Hamiltonian analysis, the quantization of the model
is discussed.Comment: Revtex, 6 pages, considerably expanded with modified title and refs.;
To appear in J.Phys.
Artificial Life in an Exciton-Polariton Lattice
We show theoretically that a lattice of exciton-polaritons can behave as a
life-like cellular automaton when simultaneously excited by a continuous wave
coherent field and a time-periodic sequence of non-resonant pulses. This
provides a mechanism of realizing a range of highly sought spatiotemporal
structures under the same conditions, including: discrete solitons, oscillating
solitons, rotating solitons, breathers, soliton trains, guns, and choatic
behaviour. These structures can survive in the system indefinitely, despite the
presence of dissipation, and allow universal computation.Comment: 14 pages, 14 figure
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