arXiv subjects
Publications and source records attributed to Hagen Kleinert.
We present a path integral formulation of 't Hooft's derivation of quantum from classical physics. Our approach is based on two concepts: Faddeev-Jackiw's treatment of constrained systems and Gozzi's path integral formulation of classical mechanics. This treatment is compared with our earlier one [quant-ph/0409021] based on Dirac-Bergmann's method.
We set up a method for a recursive calculation of the effective potential which is applied to a cubic potential with imaginary coupling. The result is resummed using variational perturbation theory (VPT), yielding an exponentially fast convergence.
We calculate the quantum phase transition for a homogeneous Bose gas in the plane of s-wave scattering length a_s and temperature T. This is done by improving a one-loop result near the interaction-free Bose-Einstein critical temperature T_c^{(0)} with the help of recent high-loop results on the shift of the critical temperature due to a weak atomic repulsion using variational perturbation theory. The quantum phase diagram shows a nose above T_c^{(0)}, so that we predict the existence of a reentrant transition above T_c^{(0)}, where an increasing repulsion leads to the formation of a condensate.
We point out that the permanent confinement in a compact 2+1-dimensional U(1) Abelian Higgs model is destroyed by matter fields in the fundamental representation. The deconfinement transition is Kosterlitz-Thouless like. The dual theory is shown to describe a three-dimensional gas of point charges with logarithmic interactions which arises from an anomalous dimension of the gauge field caused by critical matter field fluctuations. The theory is equivalent to a sine-Gordon-like theory in 2+1 dimensions with an anomalous gradient energy proportional to $k^3$. The Callan-Symanzik equation is used to demonstrate that this theory has a massless and a massive phase. The renormalization group equations for the fugacity $y(l)$ and stiffness parameter $K(l)$ of the theory show that the renormalization of $K(l)$ induces an anomalous scaling dimension $η_y$ of $y(l)$. The stiffness parameter of the theory has a universal jump at the transition determined by the dimensionality and $η_y$. As a byproduct of our analysis, we relate the critical coupling of the sine-Gordon-like theory to an {\it a priori} arbitrary constant that enters into the computation of critical exponents in the Abelian Higgs model at the charged infrared-stable fixed point of the theory, enabling a determination of this parameter. This facilitates the computation of the critical exponent $ν$ at the charged fixed point in excellent agreement with one-loop renormalization group calculations for the three-dimensional XY-model, thus confirming expectations based on duality transformations.
Several field theoretical approaches to the superconducting phase transition are discussed. Emphasis is given to theories of scaling and renormalization group in the context of the Ginzburg-Landau theory and its variants. Also discussed is the duality approach, which allows to access the strong-coupling limit of the Ginzburg-Landau theory.
We set up simple harmonic lattice models for elastic fluctuations in bcc and fcc lattices and the excitation of dislocations and disclinations. From these we derive, in a lowest approximation, universal formulas which predict melting temperatures in good agreement with the experiments. This new theory is more precise than Lindemann's rule by factor 2, and more predictive, since the size of the Lindemann number has to be fixed by experiments. In addition, our theory allows for systematic improvements.
We develop a convergent variational perturbation theory for the frequency of time-periodic solutions of nonlinear dynamical systems. The power of the theory is illustrated by applying it to the Duffing oscillator.
We present a semi-perturbative approach which yields an infrared-stable fixed point in the Ginzburg-Landau for N=2, where $N/2$ is the number of complex components. The calculations are done in $d=3$ dimensions and below $T_c$, where the renormalization group functions can be expressed directly as functions of the Ginzburg parameter $κ$ which is the ratio between the two fundamental scales of the problem, the penetration depth $λ$ and the correlation length $ξ$. We find a charged fixed point for $κ>1/\sqrt{2}$, that is, in the type II regime, where $Δκ\equivκ-1/\sqrt{2}$ is shown to be a natural expansion parameter. This parameter controls a momentum space instability in the two-point correlation function of the order field. This instability appears at a nonzero wave-vector ${\bf p}_0$ whose magnitude scales like $\simΔκ^{\barβ}$, with a critical exponent $\barβ=1/2$ in the one-loop approximation, a behavior known from magnetic systems with a Lifshitz point in the phase diagram. This momentum space instability is argued to be the origin of the negative $η$-exponent of the order field.
As a step towards deriving universal amplitude ratios of the superconductive phase transition we calculate the vacuum energy density in the symmetric phase of O(N)-symmetric scalar QED in D=4-epsilon dimensions in an epsilon-expansion using the minimal subtraction scheme commonly denoted by MS-bar. From the diverging parts of the diagrams, we obtain the renormalization constant of the vacuum Z_v which also contains information on the critical exponent alpha of the specific heat. As a side result, we use an earlier two-loop calculation of the effective potential (H.K. and B.VdB., Phys.Rev. E63 (2001) 056113, cond-mat/0104102) to determine the renormalization constant of the scalar field Z_phi up to two loops.
It is shown that permanent confinement in three-dimensional compact U(1) gauge theory can be destroyed by matter fields in a deconfinement transition. This is a consequence of a non-trivial infrared fixed point caused by matter, and an anomalous scaling dimension of the gauge field. This leads to a logarithmic interaction between the defects of the gauge-fields, which form a gas of magnetic monopoles. In the presence of logarithmic interactions, the original electric charges are unconfined. The confined phase which is permanent in the absence of matter fields is reached at a critical electric charge, where the interaction between magnetic charges is screened by a pair unbinding transition in a Kosterlitz-Thouless type of phase-transition.
I explain the geometric basis for the recently-discovered nonholonomic mapping principle which permits deriving laws of nature in spacetimes with curvature and torsion from those in flat spacetime, thus replacing and extending Einstein's equivalence principle. As an important consequence, it yields a new action principle for determining the equation of motion of a free spinless point particle in such spacetimes. Surprisingly, this equation contains a torsion force, although the action involves only the metric. This force makes trajectories autoparallel rather than geodesic. Its geometric origin is the closure failure of parallelograms in the presence of torsion, A simple generalization of the mapping principle transforms path integrals from flat spacetimes to those with curvature and torsion, thus playing the role of a quantum equivalence principle, applicable at present only to spaces with gradient torsion.
From the path integral formalism for price fluctuations with non-Gaussian distributions I derive the appropriate stochastic calculus replacing Ito's calculus for stochastic fluctuations.
We point out interesting effects of additional massless Dirac fermions with N_F colors upon the critical behavior of the Ginzburg-Landau model. For increasing N_F, the model is driven into the type II regime of superconductivity. The critical exponents are given as a function of N_F.
We develop a convergent variational perturbation theory for conditional probability densities of Markov processes. The power of the theory is illustrated by applying it to the diffusion of a particle in an anharmonic potential.
Within a path integral formalism for non-Gaussian price fluctuations we set up a simple stochastic calculus and derive a natural martingale for option pricing from the wealth balance of options, stocks, and bonds. The resulting formula is evaluated for truncated Lévy distributions.
The Ginzburg-Landau model with a Chern-Simons term is shown to possess two different scaling regimes depending on whether the mass of the scalar field is zero or not. In contrast to pure $ϕ^4$ theories, the Ginzburg-Landau model with a topologically generated mass exhibits quite different properties in perturbation theory. Our analysis suggests that the two scalings could coincide at a non-perturbative level. This view is supported by a 1/N-expansion in the massive scalar field regime.
We derive the exact dual theory of a lattice Ginzburg-Landau theory with an additional topological Chern-Simons (CS) term. It is shown that in the zero-temperature limit, the statistical parameter $θ=1/2π$ corresponds to a fixed point of the duality transformation. Thus we have found a nontrivial example of self-duality in three dimensions. In this scenario, the specialization of anyonic to fermionic statistics my be viewed as a phase transition.
Using functional derivatives with respect to free propagators and interactions we derive a closed set of Schwinger-Dyson equations in quantum electrodynamics. Its conversion to graphical recursion relations allows us to systematically generate all connected and one-particle irreducible Feynman diagrams for the $n$-point functions and the vacuum energy together with their correct weights.