Spin-density-wave instabilities in the organic conductor (TMTSF)_2ClO_4: Role of anion ordering

We study the spin-density-wave instabilities in the quasi-one-dimensional conductor (TMTSF)_2ClO_4. The orientational order of the anions ClO_4 doubles the unit cell and leads to the presence of two electrnic bands at the Fermi level. From the Ginzburg-Landau expansion of the free energy, we determine the low-temperature phase diagram as a function of the strength of the Coulomb potential due to the anions. Upon increasing the anion potential, we first find a SDW phase corresponding to an interband pairing. This SDW phase is rapidly supressed, the metallic phase being then stable down to zero temperature. The SDW instability is restored when the anion potential becomes of the order of the hopping amplitude. The metal-SDW transition corresponds to an intraband pairing which leaves half of the Fermi surface metallic. At lower temperature, a second transition, corresponding to the other intraband pairing, takes place and opens a gap on the whole Fermi surface. We discuss the consequences of our results for the experimental phase diagram of (TMTSF)_2ClO_4 at high magnetic field.Comment: 13 pages, 10 figures, Version 2 with minor correction

Remarks on the Causality, Unitarity and Supersymmetric Extension of the Lorentz and CPT-Violating Maxwell-Chern-Simons Model

The gauge-invariant Chern-Simons-type Lorentz- and CPT-breaking term is here re-assessed and issues like causality, unitarity, spontaneous gauge-symmetry breaking are investigated. Moreover, we obtain a minimal extension of such a system to a supersymmetric environment. We comment on resulting peculiar self-couplings for the gauge sector, as well as on background contribution for gaugino masses.Comment: 5 pages, NPB style, talk presented at "Renormalization Group and Anomalies in Gravity and Cosmology", Ouro Preto, Brazil, March 200

Transition to meson-dominated matter at RHIC. Consequences for kaon flow

Anisotropic flow of kaons and antikaons is studied in heavy-ion collisions at CERN SPS and BNL RHIC energies within the microscopic quark-gluon string model. In the midrapidity range the directed flow of kaons v_1 differs considerably from that of antikaons at SPS energy (E_{lab} = 160 AGeV), while at RHIC energy (\sqrt{s} = 130 AGeV) the excitation functions of both, kaon and antikaon, flows coincide within the statistical error bars. The change is attributed to formation of dense meson-dominated matter at RHIC, where the differences in interaction cross-sections of kaons and antikaons become unimportant. The time evolution of the kaon anisotropic flow is also investigated. The elliptic flow of these hadrons is found to develop at midrapidity at times 3 < t < 10 fm/c, which is much larger than the nuclear passing time t^{pass} = 0.12 fm/c. As a function of transverse momentum the elliptic flow increases almost linearly with rising p_t. It stops to rise at p_t > 1.5 GeV/c reaching the saturation value $v_2^K (p_t) \approx 10$.Comment: REVTEX, 14 pages, 4 figure

Conserved Central Domains Control the Quaternary Structure of Type I and Type II Hsp40 Molecular Chaperones

Hsp40s play an essential role in protein metabolism by regulating the polypeptide binding and release cycle of Hsp70. The Hsp40 family is large and specialized family members direct Hsp70 to perform highly specific tasks. Type I and Type II Hsp40s, such as yeast Ydj1 and Sis1, are homodimers that dictate functions of cytosolic Hsp70, but how they do so is unclear. Type I Hsp40s contain a conserved centrally located Cysteine-rich domain that is replaced by a Glycine and Methionine rich region in Type II Hsp40s, but the mechanism by which these unique domains influence Hsp40 structure and function is unknown. This is the case because high-resolution structures of full-length forms of these Hsp40s have not been solved. To fill this void we built low-resolution models of the quaternary structure of Ydj1 and Sis1 with information obtained from biophysical measurements of protein shape, small angle X-ray scattering and ab initio protein modeling. Low resolution models were also calculated for the chimeric Hsp40s YSY and SYS, in which the central domains of Ydj1 and Sis1 were exchanged. Similar to their human homologs, Ydj1 and Sis1 each has a unique shape with major structural differences apparently being the orientation of the J-domains relative to the long axis of the dimers. Central domain swapping in YSY and SYS correlates with the switched ability of YSY and SYS to perform unique functions of Sis1 and Ydj1, respectively. Models for the mechanism by which the conserved Cysteine-rich domain and Glycine and Methionine rich region confer structural and functional specificity to Type I and Type II Hsp40s are discussed

Automatic regularization by quantization in reducible representations of CCR: Point-form quantum optics with classical sources

Electromagnetic fields are quantized in manifestly covariant way by means of a class of reducible representations of CCR. $A_a(x)$ transforms as a Hermitian four-vector field in Minkowski four-position space (no change of gauge), but in momentum space it splits into spin-1 massless photons (optics) and two massless scalars (similar to dark matter). Unitary dynamics is given by point-form interaction picture, with minimal-coupling Hamiltonian constructed from fields that are free on the null-cone boundary of the Milne universe. SL(2,C) transformations and dynamics are represented unitarily in positive-norm Hilbert space describing $N$ four-dimensional oscillators. Vacuum is a Bose-Einstein condensate of the $N$-oscillator gas. Both the form of $A_a(x)$ and its transformation properties are determined by an analogue of the twistor equation. The same equation guarantees that the subspace of vacuum states is, as a whole, Poincar\'e invariant. The formalism is tested on quantum fields produced by pointlike classical sources. Photon statistics is well defined even for pointlike charges, with UV/IR regularizations occurring automatically as a consequence of the formalism. The probabilities are not Poissonian but of a R\'enyi type with $\alpha=1-1/N$. The average number of photons occurring in Bremsstrahlung splits into two parts: The one due to acceleration, and the one that remains nonzero even if motion is inertial. Classical Maxwell electrodynamics is reconstructed from coherent-state averaged solutions of Heisenberg equations. Static pointlike charges polarize vacuum and produce effective charge densities and fields whose form is sensitive to both the choice of representation of CCR and the corresponding vacuum state.Comment: 2 eps figures; in v2 notation in Eq. (39) and above Eq. (38) is correcte

Brane World Cosmology with Gauss-Bonnet Interaction

We study a Randall-Sundrum model modified by a Gauss-Bonnet interaction term. We consider, in particular, a Friedmann-Robertson-Walker metric on the brane and analyse the resulting cosmological scenario. It is shown that the usual Friedmann equations are recovered on the brane. The equation of state relating the enery density and the pressure is uniquely determined by the matching conditions. A cosmological solution with negative pressure is found.Comment: 9 pages, revtex styl

Di-Electron Bremsstrahlung in Intermediate-Energy pn and Dp Collisions

Invariant mass spectra of di-electrons stemming from bremsstrahlung processes are calculated in a covariant diagrammatical approach for the exclusive reaction D p \to p_{\rm sp} n p e^+ e^- with detection of a forward spectator proton, p_{sp}. We employ an effective nucleon-meson theory for parameterizing the sub-reaction n p \to n p e^+ e^- and, within the Bethe-Salpeter formalism, derive a factorization of the cross section in the form {d\sigma_{D p \to p_{\rm sp} n p e^+ e^-}}/{dM}= {d\sigma_{n p \to n p e^+ e^-}}/{dM} \times kinematical factor related solely to the deuteron (M is the e^+ e^- invariant mass). The effective nucleon-meson interactions, including the exchange mesons \pi, \sigma, \omega and \rho as well as excitation and radiative decay of \Delta(1232), have been adjusted to the process pp \to pp e^+ e^- at energies below the vector meson production threshold. At higher energies, contributions from \omega and \rho meson excitations are analyzed in both, NN and Dp collisions. A relation to two-step models is discussed. Subthreshold di-electron production in Dp collisions at low spectator momenta is investigated as well. Calculations have been performed for kinematical conditions envisaged for forthcoming experiments at HADES

Primeval Corrections to the CMB Anisotropies

We show that deviations of the quantum state of the inflaton from the thermal vacuum of inflation may leave an imprint in the CMB anisotropies. The quantum dynamics of the inflaton in such a state produces corrections to the inflationary fluctuations, which may be observable. Because these effects originate from IR physics below the Planck scale, they will dominate over any trans-Planckian imprints in any theory which obeys decoupling. Inflation sweeps away these initial deviations and forces its quantum state closer to the thermal vacuum. We view this as the quantum version of the cosmic no-hair theorem. Such imprints in the CMB may be a useful, independent test of the duration of inflation, or of significant features in the inflaton potential about 60 e-folds before inflation ended, instead of an unlikely discovery of the signatures of quantum gravity. The absence of any such substructure would suggest that inflation lasted uninterrupted much longer than ${\cal O}(100)$ e-folds.Comment: 17 pages, latex, no figures; v3: added references and comments, final version to appear in Phys. Rev.

Superfluidity and collective oscillations of trapped Bose-Einstein condensates in a periodical potential

Based on a unified theoretical treatment of the 1D Bogoliubov-de Genes equations, the superfluidity phenomenon of the Bose-Einstein condensates (BEC) loaded into trapped optical lattice is studied. Within the perturbation regime, an all-analytical framework is presented enabling a straightforward phenomenological mapping of the collective excitation and oscillation character of a trapped BEC where the available experimental configurations also fit.Comment: 5 pages and 2 Figs, some errors have been corrected in versions

Inflation and Preheating in NO models

We study inflationary models in which the effective potential of the inflaton field does not have a minimum, but rather gradually decreases at large $\phi$. In such models the inflaton field does not oscillate after inflation, and its effective mass becomes vanishingly small, so the standard theory of reheating based on the decay of the oscillating inflaton field does not apply. For a long time the only mechanism of reheating in such non-oscillatory (NO) models was based on gravitational particle production in an expanding universe. This mechanism is very inefficient. We will show that it may lead to cosmological problems associated with large isocurvature fluctuations and overproduction of dangerous relics such as gravitinos and moduli fields. We also note that the setting of initial conditions for the stage of reheating in these models should be reconsidered. All of these problems can be resolved in the context of the recently proposed scenario of instant preheating if there exists an interaction ${g^2} \phi^2\chi^2$ of the inflaton field $\phi$ with another scalar field $\chi$. We show that the mechanism of instant preheating in NO models is much more efficient than the usual mechanism of gravitational particle production even if the coupling constant $g^2$ is extremely small, $10^{-14} \ll g^2 \ll 1$.Comment: 10 pages, revte