9,509 research outputs found

    Spin Polarisability of the Nucleon in the Heavy Baryon Effective Field Theory

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    We have constructed a heavy baryon effective field theory with photon as an external field in accordance with the symmetry requirements similar to the heavy quark effective field theory. By treating the heavy baryon and anti-baryon equally on the same footing in the effective field theory, we have calculated the spin polarisabilities γi,i=1...4\gamma_i, i=1...4 of the nucleon at third order and at fourth-order of the spin-dependent Compton scattering. At leading order (LO), our results agree with the corresponding results of the heavy baryon chiral perturbation theory, at the next-to-leading order(NLO) the results show a large correction to the ones in the heavy baryon chiral perturbation theory due to baryon-antibaryon coupling terms. The low energy theorem is satisfied both at LO and at NLO. The contributions arising from the heavy baryon-antibaryon vertex were found to be significant and the results of the polarisabilities obtained from our theory is much closer to the experimental data.Comment: 21pages, title changed, minimal correction

    Renormalization of the Cabibbo-Kobayashi-Maskawa Quark Mixing Matrix

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    We have investigated the present renormalization prescriptions of Cabibbo-Kobayashi-Maskawa (CKM) matrix. When considering the prescription which is formulated with reference to the case of zero mixing we find it doesn't satisfy the unitary condition of the bare CKM matrix. After added a delicate patch this problem can be solved at one-loop level. In this paper We generalize this prescription to all loop levels and keep the unitarity of the bare CKM matrix, simultaneously make the amplitude of an arbitrary physical process involving quark mixing convergent and gauge independent. We also find that in order to keep the CKM counterterms gauge independent the unitarity of the bare CKM matrix must be preserved.Comment: has been revised, 8 pages, 1 figur

    Multiple stellar populations in the Galactic globular cluster NGC 6752

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    We have carried out high-precision photometry on a large number of archival HST images of the Galactic globular cluster NGC 6752, to search for signs of multiple stellar populations. We find a broadened main sequence, and demonstrate that this broadening cannot be attributed either to binaries or to photometric errors. There is also some indication of a main-sequence split. No significant spread could be found along the subgiant branch, however. Ground-based photometry reveals that in the U vs. (U-B) color-magnitude diagram the red-giant branch exhibits a clear color spread, which we have been able to correlate with variations in Na and O abundances. In particular the Na-rich, O-poor stars identified by Carretta et al. (2007) define a sequence on the red side of the red-giant branch, while Na-poor, O-rich stars populate a bluer, more dispersed portion of the red-giant branch.Comment: 31 pages, 12 figures; Accepted for Publication in the Astrophysical Journa

    Optical conductivity in the normal state fullerene superconductors

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    We calculate the optical conductivity, σ(ω)\sigma(\omega), in the normal state fullerene superconductors by self-consistently including the impurity scatterings, the electron-phonon and electron-electron Coulomb interactions. The finite bandwidth of the fullerenes is explicitely considered, and the vertex corection is included aa lala Nambu in calculating the renormalized Green's function. σ(ω)\sigma(\omega) is obtained by calculating the current-current correlation function with the renormalized Green's function in the Matsubara frequency and then performing analytic continuation to the real frequency at finite temperature. The Drude weight in σ(ω)\sigma(\omega) is strongly suppressed due to the interactions and transfered to the mid-infrared region around and above 0.06 eV which is somewhat less pronounced and much broader compared with the expermental observation by DeGiorgi etet alal.Comment: 6 pages, 4 figures. To be published in Physical Review B, July 1

    A New Method of Probing the Phonon Mechanism in Superconductors including MgB2_{2}

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    Weak localization has a strong influence on both the normal and superconducting properties of metals. In particular, since weak localization leads to the decoupling of electrons and phonons, the temperature dependence of resistance (i.e., λtr\lambda_{tr}) is decreasing with increasing disorder, as manifested by Mooij's empirical rule. In addition, Testardi's universal correlation of TcT_{c} (i.e., λ\lambda) and the resistance ratio (i.e., λtr\lambda_{tr}) follows. This understanding provides a new means to probe the phonon mechanism in superconductors including MgB2_{2}. The merits of this method are its applicability to any superconductors and its reliability because the McMillan's electron-phonon coupling constant λ\lambda and λtr\lambda_{tr} change in a broad range, from finite values to zero, due to weak localization. Karkin et al's preliminary data of irradiated MgB2_{2} show the Testardi correlation, indicating that the dominant pairing mechanism in MgB2_{2} is the phonon-mediated interaction.Comment: 9 pages, latex, 3 figure

    Coulomb suppression of NMR coherence peak in fullerene superconductors

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    The suppressed NMR coherence peak in the fullerene superconductors is explained in terms of the dampings in the superconducting state induced by the Coulomb interaction between conduction electrons. The Coulomb interaction, modelled in terms of the onsite Hubbard repulsion, is incorporated into the Eliashberg theory of superconductivity with its frequency dependence considered self-consistently at all temperatures. The vertex correction is also included via the method of Nambu. The frequency dependent Coulomb interaction induces the substantial dampings in the superconducting state and, consequently, suppresses the anticipated NMR coherence peak of fullerene superconductors as found experimentally.Comment: 4 pages, Revtex, and 2 figures. Revised and final version to appear in Phys. Rev. Lett. (1998

    Unusual T_c variation with hole concentration in Bi_2Sr_{2-x}La_xCuO_{6+\delta}

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    We have investigated the TcT_c variation with the hole concentration pp in the La-doped Bi 2201 system, Bi2_2Sr2x_{2-x}Lax_xCuO6+δ_{6+\delta}. It is found that the Bi 2201 system does not follow the systematics in TcT_c and pp observed in other high-TcT_c cuprate superconductors (HTSC's). The TcT_c vs pp characteristics are quite similar to what observed in Zn-doped HTSC's. An exceptionally large residual resistivity component in the inplane resistivity indicates that strong potential scatterers of charge carriers reside in CuO2_2 planes and are responsible for the unusual TcT_c variation with pp, as in the Zn-doped systems. However, contrary to the Zn-doped HTSC's, the strong scatter in the Bi 2201 system is possibly a vacancy in the Cu site.Comment: RevTeX, 3 figures, to be published in the Physical Review

    Sommerfeld's quantum condition of action and the spectra of Schwarzschild black hole

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    If the situation of quantum gravity nowadays is nearly the same as that of the quantum mechanics in it's early time of Bohr and Sommerfeld, then a first step study of the quantum gravity from Sommerfeld's quantum condition of action might be helpful. In this short paper the spectra of Schwarzschild black hole(SBH) in quasi-classical approach of quantum mechanics is given. We find the quantum of area, the quantum of entropy and the Hawking evaporation will cease as the black hole reaches its ground state.Comment: 7 pages, no figures, submitted to Classical and Quantum Gravit
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