arXiv subjects

Qing-hai Wang

Publications and source records attributed to Qing-hai Wang.

43 records · Page 3Linked to original sources

arXiv2010

Probability Density in the Complex Plane

The correspondence principle asserts that quantum mechanics resembles classical mechanics in the high-quantum-number limit. In the past few years many papers have been published on the extension of both quantum mechanics and classical mechanics into the complex domain. However, the question of whether complex quantum mechanics resembles complex classical mechanics at high energy has not yet been studied. This paper introduces the concept of a local quantum probability density $ρ(z)$ in the complex plane. It is shown that there exist infinitely many complex contours $C$ of infinite length on which $ρ(z) dz$ is real and positive. Furthermore, the probability integral $\int_Cρ(z) dz$ is finite. Demonstrating the existence of such contours is the essential element in establishing the correspondence between complex quantum and classical mechanics. The mathematics needed to analyze these contours is subtle and involves the use of asymptotics beyond all orders.

hep-th↗

arXiv2009

Complex Correspondence Principle

Quantum mechanics and classical mechanics are two very different theories, but the correspondence principle states that quantum particles behave classically in the limit of high quantum number. In recent years much research has been done on extending both quantum mechanics and classical mechanics into the complex domain. This letter shows that these complex extensions continue to exhibit a correspondence, and that this correspondence becomes more pronounced in the complex domain. The association between complex quantum mechanics and complex classical mechanics is subtle and demonstrating this relationship prequires the use of asymptotics beyond all orders.

hep-th↗

arXiv2009

Level Crossings in Complex Two-Dimensional Potentials

Two-dimensional PT-symmetric quantum-mechanical systems with the complex cubic potential V_{12}=x^2+y^2+igxy^2 and the complex Henon-Heiles potential V_{HH}=x^2+y^2+ig(xy^2-x^3/3) are investigated. Using numerical and perturbative methods, energy spectra are obtained to high levels. Although both potentials respect the PT symmetry, the complex energy eigenvalues appear when level crossing happens between same parity eigenstates.

quant-ph↗

arXiv2006

Multidimensional Worldline Instantons

We extend the worldline instanton technique to compute the vacuum pair production rate for spatially inhomogeneous electric background fields, with the spatial inhomogeneity being genuinely two or three dimensional, both for the magnitude and direction of the electric field. Other techniques, such as WKB, have not been applied to such higher dimensional problems. Our method exploits the instanton dominance of the worldline path integral expression for the effective action.

hep-th↗

arXiv2006

Fluctuations about Cosmological Instantons

We study the semiclassical fluctuation problem around bounce solutions for a self-interacting scalar field in curved space. As in flat space, the fluctuation problem separates into partial waves labeled by an integer l, and we determine the large l behavior of the fluctuation determinants, a quantity needed to define a finite fluctuation prefactor. We also show that while the Coleman-De Luccia bounce solution has a single negative mode in the l=0 sector, the oscillating bounce solutions also have negative modes in partial waves higher than the s-wave, further evidence that they are not directly related to quantum tunneling.

hep-th↗

arXiv2006

Worldline Instantons II: The Fluctuation Prefactor

In a previous paper [1], it was shown that the worldline expression for the nonperturbative imaginary part of the QED effective action can be approximated by the contribution of a special closed classical path in Euclidean spacetime, known as a worldline instanton. Here we extend this formalism to compute also the prefactor arising from quantum fluctuations about this classical closed path. We present a direct numerical approach for determining this prefactor, and we find a simple explicit formula for the prefactor in the cases where the inhomogeneous electric field is a function of just one spacetime coordinate. We find excellent agreement between our semiclassical approximation, conventional WKB, and recent numerical results using numerical worldline loops.

hep-th↗

arXiv2005

Secondary pairing in gapless color-superconducting quark matter

We calculate secondary pairing in a model of a color superconductor with a quadratic gapless dispersion relation for the quasiquarks of the primary pairing. Our model mimics the physics of the sector of blue up and red strange quarks in gapless color-flavor-locked quark matter. The secondary pairing opens up a gap Delta_s in the quark spectrum, and we confirm Hong's prediction that in typical secondary channels Delta_s is proportional to G_s^2 for coupling strength G_s. This shows that the large density of states of the quadratically gapless mode greatly enhances the secondary pairing over the standard BCS result, in which Delta is proportional to exp(-const/G). In all of the secondary channels that we analyzed we find that the secondary gap, even with this enhancement, is from ten to hundreds of times smaller than the primary gap at reasonable values of the secondary coupling, indicating that secondary pairing does not generically resolve the magnetic instability of the gapless phase.

hep-ph↗