Complex Lagrangians and phantom cosmology

Motivated by the generalization of quantum theory for the case of non-Hermitian Hamiltonians with PT symmetry, we show how a classical cosmological model describes a smooth transition from ordinary dark energy to the phantom one. The model is based on a classical complex Lagrangian of a scalar field. Specific symmetry properties analogous to PT in non-Hermitian quantum mechanics lead to purely real equation of motion.Comment: 11 pages, to be published in J.Phys.A, refs. adde

Phantom universe from CPT symmetric QFT

Inspired by the generalization of quantum theory for the case of non-Hermitian Hamiltonians with CPT symmetry, we construct a simple classical cosmological scalar field based model describing a smooth transition from ordinary dark energy to the phantom one

Equivalence of the super Lax and local Dunkl operators for Calogero-like models

Following Shastry and Sutherland I construct the super Lax operators for the Calogero model in the oscillator potential. These operators can be used for the derivation of the eigenfunctions and integrals of motion of the Calogero model and its supersymmetric version. They allow to infer several relations involving the Lax matrices for this model in a fast way. It is shown that the super Lax operators for the Calogero and Sutherland models can be expressed in terms of the supercharges and so called local Dunkl operators constructed in our recent paper with M. Ioffe. Several important relations involving Lax matrices and Hamiltonians of the Calogero and Sutherland models are easily derived from the properties of Dunkl operators.Comment: 25 pages, Latex, no figures. Accepted for publication in: Jounal of Physics A: Mathematical and Genera

Dynamical Lorentz simmetry breaking from 3+1 Axion-Wess-Zumino model

We study the renormalizable abelian vector-field models in the presence of the Wess-Zumino interaction with the pseudoscalar matter. The renormalizability is achieved by supplementing the standard kinetic term of vector fields with higher derivatives. The appearance of fourth power of momentum in the vector-field propagator leads to the super-renormalizable theory in which the $\beta$-function, the vector-field renormalization constant and the anomalous mass dimension are calculated exactly. It is shown that this model has the infrared stable fixed point and its low-energy limit is non-trivial. The modified effective potential for the pseudoscalar matter leads to the possible occurrence of dynamical breaking of the Lorentz symmetry. This phenomenon is related to the modification of Electrodynamics by means of the Chern-Simons (CS) interaction polarized along a constant CS vector. Its presence makes the vacuum optically active that has been recently estimated from astrophysical data. We examine two possibilities for the CS vector to be time-like or space-like, under the assumption that it originates from v.e.v. of some pseudoscalar matter and show that only the latter one is consistent in the framework of the AWZ model, because a time-like CS vector makes the vacuum unstable under pairs creation of tachyonic photon modes with the finite vacuum decay rate.Comment: 33 pages, no Figures, Plain TeX, submitted to Phys. Rev.

Negative Magnetoresistance in (In,Mn)As

The magnetotransport properties of an In0.95Mn0.05As thin film grown by metal-organic vapor phase epitaxy were measured. Resistivity was measured over the temperature range of 5 to 300 K. The resistivity decreased with increasing temperature from 90 ohm-cm to 0.05 ohm-cm. The field dependence of the low temperature magnetoresistance was measured. A negative magnetoresistance was observed below 17 K with a hysteresis in the magnetoresistance observed at 5 K. The magnetoresistance as a function of applied field was described by the Khosla-Fischer model for spin scattering of carriers in an impurity band.Comment: 8 pages, 4 figures, accepted to Physical Review

Spontaneous Breaking of Lorentz Invariance

We describe how a stable effective theory in which particles of the same fermion number attract may spontaneously break Lorentz invariance by giving non-zero fermion number density to the vacuum (and therefore dynamically generating a chemical potential term). This mecanism yields a finite vacuum expectation value $$which we consider in the context of proposed models that require such a breaking of Lorentz invariance in order to yield composite degrees of freedom that act approximately like gauge bosons. We also make general remarks about how the background source provided by$$ could relate to work on signals of Lorentz violation in electrodynamics.Comment: revtex4, 11 pages, 5 figures; v2:references added; v3:more references added, typos fixed, some points in sect. IV clarified; v4:even more references added, discussion in sect. V extended; v5:replaced to match published version (minor corrections of form

Distinct mechanisms of signal processing by lamina I spino-parabrachial neurons

Lamina I spino-parabrachial neurons (SPNs) receive peripheral nociceptive input, process it and transmit to the supraspinal centres. Although responses of SPNs to cutaneous receptive field stimulations have been intensively studied, the mechanisms of signal processing in these neurons are poorly understood. Therefore, we used an ex-vivo spinal cord preparation to examine synaptic and cellular mechanisms determining specific input-output characteristics of the neurons. The vast majority of the SPNs received a few direct nociceptive C-fiber inputs and generated one spike in response to saturating afferent stimulation, thus functioning as simple transducers of painful stimulus. However, 69% of afferent stimulation-induced action potentials in the entire SPN population originated from a small fraction (19%) of high-output neurons. These neurons received a larger number of direct Ad- and C-fiber inputs, generated intrinsic bursts and efficiently integrated a local network activity via NMDA-receptor-dependent mechanisms. The high-output SPNs amplified and integrated the nociceptive input gradually encoding its intensity into the number of generated spikes. Thus, different mechanisms of signal processing allow lamina I SPNs to play distinct roles in nociception.The authors thank Mr. Andrew Dromaretsky for the technical assistance. P.B. was supported by the National Academy of Sciences of Ukraine (NASU), grant NASU # 0116U004470, grant NASU#67/15-Н. N.V. was supported by the NASU Biotechnology and NASU-KNU grants; NIH 1R01NS113189-01. B.V.S. was supported by the FEDER funds through the COMPETE 2020 (POCI), Portugal 2020, and by the FCT project PTDC/NEU-NMC/1259/2014 (POCI-01-0145-FEDER-016588

Quantum toboggans: models exhibiting a multisheeted PT symmetry

A generalization of the concept of PT-symmetric Hamiltonians H=p^2+V(x) is described. It uses analytic potentials V(x) (with singularities) and a generalized concept of PT-symmetric asymptotic boundary conditions. Nontrivial toboggans are defined as integrated along topologically nontrivial paths of coordinates running over several Riemann sheets of wave functions.Comment: 16 pp, 5 figs. Written version of the talk given during 5th International Symposium on Quantum Theory and Symmetries, University of Valladolid, Spain, July 22 - 28 2007, webpage http://tristan.fam.uva.es/~qts

Parity doubling in particle physics

Parity doubling in excited hadrons is reviewed. Parity degeneracy in hadrons was first experimentally observed 40 years ago. Recently new experimental data on light mesons caused much excitement and renewed interest to the phenomenon, which still remains to be enigmatic. The present retrospective review is an attempt to trace the history of parity doubling phenomenon, thus providing a kind of introduction to the subject. We begin with early approaches of 1960s (Regge theory and dynamical symmetries) and end up with the latest trends (manifestations of broader degeneracies and AdS/QCD). We show the evolution of various ideas about parity doubling. The experimental evidence for this phenomenon is scrutinized in the non-strange sector. Some experiments of 1960s devoted to the search for missing non-strange bosons are re-examined and it is argued that results of these experiments are encouraging from the modern perspective.Comment: Version to appear in Int. J. Mod. Phys. A, 63 pages, 9 figure