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Normal State Spectral Lineshapes of Nodal Quasiparticles in Single Layer Bi2201 Superconductor

Description: A detailed study of the normal state photoemission lineshapes and quasiparticle dispersion for the single layer Bi{sub 2}Sr{sub 2-x}La{sub x}CuO{sub 6+{delta}}(Bi2201) superconductor is presented. We report the first experimental evidence of a double peak structure and a dip of spectral intensity in the energy distribution curves (EDCs) along the nodal direction. The double peak structure is well identified in the normal state, up to ten times the critical temperature. As a result of the same self-energy effect, a strong mass renormalization of the quasiparticle dispersion, i.e. kink, and an increase of the quasiparticle lifetime in the normal state are also observed. Our results provide unambiguous evidence on the existence of bosonic excitation in the normal state, and support a picture where nodal quasiparticles are strongly coupled to the lattice.
Date: April 30, 2010
Creator: Lanzara, A.
Partner: UNT Libraries Government Documents Department

The charm quark mass to two-loop order

Description: The truncation of the perturbative series at one loop order for the mass renormalization constants remain a significant systematic uncertainty in the determination of heavy quark masses in lattice QCD. We present here a high beta Monte Carlo calculation of the two loop mass renormalization constant for clover-improved fermions near the charm mass in the Fermilab heavy quark formalism. A preliminary value for the charm quark mass in the {ovr MS} scheme at two loop order is reported.
Date: October 23, 2001
Creator: Juge, Keisuke Jimmy
Partner: UNT Libraries Government Documents Department

Two-loop perturbative quark mass renormalization from large {beta} Monte Carlo

Description: We present the calculation of heavy Wilson quark mass renormalization constants from large beta Monte Carlo simulations. Simulations were performed at various beta larger than 9, each on several spatial lattice sizes to allow for an infinite volume extrapolation. We use twisted boundary conditions to suppress tunneling and work in Coulomb gauge with appropriate adjustments for the temporal links. The one-loop coefficient obtained from this method is in agreement with the analytical result and a preliminary result for the second order coefficient is reported.
Date: February 14, 2001
Creator: Juge, Keisuke Jimmy
Partner: UNT Libraries Government Documents Department

Direct observation of the mass renormalization in SrVO3 by angle resolved photoemission spectroscopy

Description: We have performed an angle-resolved photoemission study of the three-dimensional perovskite-type SrVO{sub 3}. Observed spectral weight distribution of the coherent part in the momentum space shows cylindrical Fermi surfaces consisting of the V 3d t{sub 2g} orbitals as predicted by local-density approximation (LDA) band-structure calculation. The observed energy dispersion shows a moderately enhanced effective mass compared to the LDA results, corresponding to the effective mass enhancement seen in the thermodynamic properties. Contributions from the bulk and surface electronic structures to the observed spectra are discussed based on model calculations.
Date: May 3, 2010
Creator: Yoshida, t.
Partner: UNT Libraries Government Documents Department

Reduction of Quark Mass Scheme Dependence in B bar -> Xs gamma at the NNLL Level

Description: The uncertainty of the theoretical prediction of the B {yields} X{sub s}{gamma} branching ratio at NLL level is dominated by the charm mass renormalization scheme ambiguity. In this paper we calculate those NNLL terms which are related to the renormalization of m{sub c}, in order to get an estimate of the corresponding uncertainty at the NNLL level. We find that these terms significantly reduce (by typically a factor of two) the error on BR(B {yields} X{sub s}{gamma}) induced by the definition of m{sub c}. Taking into account the experimental accuracy of around 10% and the future prospects of the B factories, we conclude that a NNLL calculation would increase the sensitivity of the observable B {yields} X{sub s}{gamma} to possible new degrees of freedom beyond the SM significantly.
Date: June 20, 2005
Creator: Asatrian, H.M.; Inst., /Yerevan Phys.; Greub, C.; U., /Bern; Hovhannisyan, A.; Inst., /Yerevan Phys. et al.
Partner: UNT Libraries Government Documents Department

Towards the NNLL Precision in the Decay $\bar B \rightarrow X_s \gamma$

Description: The present NLL prediction for the decay rate of the rare inclusive process {bar B} {yields} X{sub s}{gamma} has a large uncertainty due to the charm mass renormalization scheme ambiguity. We estimate that this uncertainty will be reduced by a factor of 2 at the NNLL level. This is a strong motivation for the on-going NNLL calculation, which will thus significantly increase the sensitivity of the observable {bar B} {yields} X{sub s}{gamma} to possible new degrees of freedom beyond the SM. We also give a brief status report of the NNLL calculation.
Date: January 5, 2006
Creator: Asatrian, Hrachia M.; Hovhannisyan, Artyom; Poghosyan, Vahagn; Inst., /Yerevan Phys.; Greub, Christoph; U., /Bern et al.
Partner: UNT Libraries Government Documents Department

PHOTOEMISSION AS A PROBE OF THE COLLECTIVE EXCITATIONS IN CONDENSED MATTER SYSTEMS.

Description: New developments in instrumentation have recently allowed photoemission measurements to be performed with very high energy and momentum resolution.[1] This has allowed detailed studies of the self-energy corrections to the lifetime and mass renormalization of excitations in the vicinity of the Fermi level. These developments come at an opportune time. Indeed the discovery of high temperature superconductivity in the cuprates and related systems is presenting a range of challenges for condensed matter physics.[2] Does the mechanism of high T{sub c} superconductivity represent new physics? Do we need to go beyond Landau's concept of the Fermi liquid?[3] What, if any, is the evidence for the presence or absence of quasiparticles in the excitation spectra of these complex oxides? The energy resolution of the new instruments is comparable to or better than the energy or temperature scale of superconductivity and the energy of many collective excitations. As such, photoemission has again become recognized as an important probe of condensed matter. Studies of the high T{sub c} superconductors and related materials are aided by the observation that they are two dimensional. To understand this, we note that the photoemission process results in both an excited photoelectron and a photohole in the final state. Thus the experimentally measured photoemission peak is broadened to a width reflecting contributions from both the finite lifetime of the photohole and the momentum broadening of the outgoing photoelectron.
Date: August 1, 2006
Creator: JOHNSON, P.D. & VALLA, T.
Partner: UNT Libraries Government Documents Department

Calculability of the n-p mass difference in gauge theories

Description: The requirement of a calculable n-p mass difference leads to a consideration of unified gauge theories. Future developments in grand unified models may provide a realistic framework for the calculation of the n-p mass difference. The possibility that the relatively soft ultraviolet behavior of QCD softens the divergence in the lowest-order electromagnetic mass shift is considered in detail. It is shown that, if the bare mass and QCD coupling are constrained to be independent of the electromagnetic coupling, as is natural, then the lowest-order electromagnetic shifts of the renormalized mass and QCD coupling are infinite.
Date: January 1, 1980
Creator: Kiskis, J.
Partner: UNT Libraries Government Documents Department