The Nucleon Spectral Function at Finite Temperature and the Onset of Superfluidity in Nuclear Matter

Nucleon selfenergies and spectral functions are calculated at the saturation density of symmetric nuclear matter at finite temperatures. In particular, the behaviour of these quantities at temperatures above and close to the critical temperature for the superfluid phase transition in nuclear matter is discussed. It is shown how the singularity in the thermodynamic T-matrix at the critical temperature for superfluidity (Thouless criterion) reflects in the selfenergy and correspondingly in the spectral function. The real part of the on-shell selfenergy (optical potential) shows an anomalous behaviour for momenta near the Fermi momentum and temperatures close to the critical temperature related to the pairing singularity in the imaginary part. For comparison the selfenergy derived from the K-matrix of Brueckner theory is also calculated. It is found, that there is no pairing singularity in the imaginary part of the selfenergy in this case, which is due to the neglect of hole-hole scattering in the K-matrix. From the selfenergy the spectral function and the occupation numbers for finite temperatures are calculated.Comment: LaTex, 23 pages, 21 PostScript figures included (uuencoded), uses prc.sty, aps.sty, revtex.sty, psfig.sty (last included

Critical Enhancement of the In-medium Nucleon-Nucleon Cross Section at low Temperatures

The in-medium nucleon-nucleon cross section is calculated starting from the thermodynamic T-matrix at finite temperatures. The corresponding Bethe-Salpeter-equation is solved using a separable representation of the Paris nucleon-nucleon-potential. The energy-dependent in-medium N-N cross section at a given density shows a strong temperature dependence. Especially at low temperatures and low total momenta, the in-medium cross section is strongly modified by in-medium effects. In particular, with decreasing temperature an enhancement near the Fermi energy is observed. This enhancement can be discussed as a precursor of the superfluid phase transition in nuclear matter.Comment: 10 pages with 4 figures (available on request from the authors), MPG-VT-UR 34/94 accepted for publication in Phys. Rev.

Spontaneous breaking of rotational symmetry in superconductors

We show that homogeneous superconductors with broken spin/isospin symmetry lower their energy via a transition to a novel superconducting state where the Fermi-surfaces are deformed to a quasi-ellipsoidal form at zero total momentum of Cooper pairs. In this state, the gain in the condensation energy of the pairs dominates over the loss in the kinetic energy caused by the lowest order (quadrupole) deformation of Fermi-surfaces from the spherically symmetric form. There are two energy minima in general, corresponding to the deformations of the Fermi-spheres into either prolate or oblate forms. The phase transition from spherically symmetric state to the superconducting state with broken rotational symmetry is of the first order.Comment: 5 pages, including 3 figures, published versio

Corrections to Tribimaximal Mixing from Nondegenerate Phases

We propose a seesaw scenario that possible corrections to the tribimaximal pattern of lepton mixing are due to the small phase splitting of the right-handed neutrino mass matrix. we show that the small deviations can be expressed analytically in terms of two splitting parameters($\delta_1$ and $\delta_2$) in the leading order. The solar mixing angle $\theta_{12}$ favors a relatively smaller value compared to zero order value ($35.3^\circ$), and the Dirac type CP phase $\delta$ chooses a nearly maximal one. The two Majorana type CP phases $\rho$ and $\sigma$ turn out to be a nearly linear dependence. Also a normal hierarchy neutrino mass spectrum is favored due to the stability of perturbation calculations.Comment: 19 pages 6 figures, Accepted by Mod. Phy. Lett.

In medium T-matrix for superfluid nuclear matter

We study a generalized ladder resummation in the superfluid phase of the nuclear matter. The approach is based on a conserving generalization of the usual T-matrix approximation including also anomalous self-energies and propagators. The approximation here discussed is a generalization of the usual mean-field BCS approach and of the in medium T-matrix approximation in the normal phase. The numerical results in this work are obtained in the quasi-particle approximation. Properties of the resulting self-energy, superfluid gap and spectral functions are studied.Comment: 38 pages, 19 figures, Introduction rewritten, Refs. adde

Nuclear Self-energy and Realistic Interactions

The structure of nucleon self-energy in nuclear matter is evaluated for various realistic models of the nucleon-nucleon (NN) interaction. Starting from the Brueckner-Hartree-Fock approximation without the usual angle-average approximation, the effects of hole-hole contributions and a self-consistent treatment within the framework of the Green function approach are investigated. Special attention is paid to the predictions for the spectral function originating from various models of the NN interaction which all yield an accurate fit for the NN phase shifts.Comment: 26 pages, 12 figure

Four-particle condensate in strongly coupled fermion systems

Four-particle correlations in fermion systems at finite temperatures are investigated with special attention to the formation of a condensate. Instead of the instability of the normal state with respect to the onset of pairing described by the Gorkov equation, a new equation is obtained which describes the onset of quartetting. Within a model calculation for symmetric nuclear matter, we find that below a critical density, the four-particle condensation (alpha-like quartetting) is favored over deuteron condensation (triplet pairing). This pairing-quartetting competition is expected to be a general feature of interacting fermion systems, such as the excition-biexciton system in excited semiconductors. Possible experimental consequences are pointed out.Comment: LaTeX, 11 pages, 2 figures, uses psfig.sty (included), to be published in Phys. Rev. Lett., tentatively scheduled for 13 April 1998 (Volume 80, Number 15

Thermodynamics of nn-pp condensate in asymmetric nuclear matter

We study the neutron-proton pairing in nuclear matter as a function of isospin asymmetry at finite temperatures and the saturation density using realistic nuclear forces and Brueckner-renormalized single particle spectra. Our computation of the thermodynamic quantities shows that while the difference of the entropies of the superconducting and normal phases anomalously changes its sign as a function of temperature for arbitrary asymmetry, the grand canonical potential does not; the superconducting state is found to be stable in the whole temperature-asymmetry plane. The pairing gap completely disappears for density-asymmetries exceeding $\alpha_c= (n_n-n_p)/n \simeq 0.11$.Comment: 7 pages, including 3 figures, uses revte

A Self-Consistent Solution to the Nuclear Many-Body Problem at Finite Temperature

The properties of symmetric nuclear matter are investigated within the Green's functions approach. We have implemented an iterative procedure allowing for a self-consistent evaluation of the single-particle and two-particle propagators. The in-medium scattering equation is solved for a realistic (non-separable) nucleon-nucleon interaction including both particle-particle and hole-hole propagation. The corresponding two-particle propagator is constructed explicitely from the single-particle spectral functions. Results are obtained for finite temperatures and an extrapolation to T=0 is presented.Comment: 11 pages 5 figure

Izučavanje morfologije jajnika i citologije jajne ćelije kao osnova za uspostavljanje metoda IVM, IVF i embriotransfera

In three types of domestic animals: cattle, pigs and sheep, morphology of ovary was studied. Results such as differences in shape, size within and between species, number of follicles in maturation, changes in sex cycle, connection of follicles in maturation are presented in figures. By method of aspiration, oocytes were isolated from ovaries and their cytology analyzed as the first step in methods of in vitro maturation (IVM), followed by in vitro fertilization (IVF) and embryo transfer. These methods are wide spread in modern livestock production (cattle, horses) since they have many advantages of which the most important is to obtain more offspring from high quality female heads. Method has disadvantage: potential diminishing of biodiversity, therefore special attention is necessary in order not to endanger biodiversity and still get more offspring with high production abilities and traits. IVM, IVF and embryo transfer represent new approach to selection, fast and with similar effect like in conventional artificial insemination, therefore they should be applied in practice also in our country.Kod tri vrste domaćih životinja: goveda, svinja i ovaca, izučavana je morfologija jajnika. Rezultati: razlika u obliku, veličini inter i intraspecies, broj folikula u zrenju, promene tokom polnog ciklusa, povezanost folikula u zrenju; prikazani su na slikama. Iz jajnika su metodom aspiracije iz jajnika izolovane jajne ćelije i analizirana njihova citologija kao prvi korak u metodi in vitro sazrevanja (IVM), nakon koje slede in vitro oplodnja (IVF) i embriotransfer. Ove metode su široko rasprostranjene u modernom stočarstvu (goveda, konji) jer imaju niz prednosti od kojih je najvažnije dobijanje većeg broja potomaka od kvalitetnih ženskih grla. Metoda ima i nedostatak: moguće smanjenje biodiverziteta, i stoga treba voditi računa da se biodiverzitet ne ugrozi, a da se dobije veći broj potomstva sa visokim proizvodnim osobinama. IVM, IVF i embriotransfer su nov pristup selekciji, brzi, a sa sličnim efektom kao kod klasične veštačke selekcije, i zbog toga bi bilo dobro da nađu primenu i na našim prostorima