989 research outputs found
Renormalization of the antisymmetric tensor field propagator and dynamical generation of the mesons in Resonance Chiral Theory
We discuss the renormalization of the vector meson propagator within
Resonance chiral theory at one loop. Using the particular form of the
interaction Lagrangian we show that additional poles of the renormalized
propagator corresponding to degrees of freedom can be generated. We
give a concrete example of such an effect.Comment: 4 pages, 1 figure, to appear in Proceedings of the conference QCD 08,
Montpellier, 7-12 July 200
High energy constraints in the octet SS-PP correlator and resonance saturation at NLO in 1/Nc
We study the octet SS-PP correlator within resonance chiral theory up to the
one-loop level, i.e., up to next-to-leading order in the 1/Nc expansion. We
will require that our correlator follows the power behaviour prescribed by the
operator product expansion at high euclidian momentum. Nevertheless, we will
not make use of short-distance constraints from other observables. Likewise,
the high-energy behaviour will be demanded for the whole correlator, not for
individual absorptive channels. The amplitude is progressively improved by
considering more and more complicated operators in the hadronic lagrangian.
Matching the resonance chiral theory result with chiral perturbation theory at
low energies produces the estimates L_8(mu)^{SU(3)} = (1.0+-0.4)10^-3 and
C_{38}(mu)^{SU(3)} = (8+-5) 10^-6 for mu=770 MeV. The effect of alternative
renormalization schemes is also discussed in the article.Comment: 40 pages, 18 figure
Renormalization and additional degrees of freedom within the chiral effective theory for spin-1 resonances
We study in detail various aspects of the renormalization of the spin-1
resonance propagator in the effective field theory framework. First, we briefly
review the formalisms for the description of spin-1 resonances in the path
integral formulation with the stress on the issue of propagating degrees of
freedom. Then we calculate the one-loop 1-- meson self-energy within the
Resonance chiral theory in the chiral limit using different methods for the
description of spin-one particles, namely the Proca field, antisymmetric tensor
field and the first order formalisms. We discuss in detail technical aspects of
the renormalization procedure which are inherent to the power-counting
non-renormalizable theory and give a formal prescription for the organization
of both the counterterms and one-particle irreducible graphs. We also construct
the corresponding propagators and investigate their properties. We show that
the additional poles corresponding to the additional one-particle states are
generated by loop corrections, some of which are negative norm ghosts or
tachyons. We count the number of such additional poles and briefly discuss
their physical meaning.Comment: 65 pages, 12 figure
Spin-charge separation in Aharonov-Bohm rings of interacting electrons
We investigate the properties of strongly correlated electronic models on a
flux-threaded ring connected to semi-infinite free-electron leads. The
interference pattern of such an Aharonov-Bohm ring shows sharp dips at certain
flux values, determined by the filling, which are a consequence of spin-charge
separation in a nanoscopic system.Comment: 4 pages, 3 figures, to appear in Phys. Rev. Let
Unconventional properties of superconducting cuprates
We present an explanation of the unusual peak/dip/hump features observed in
photoemission experiments on Bi2212 at . We argue that these
features arise from the interaction of the fermionic quasi-particles with
overdamped spin fluctuations. We show that the strong spin-fermion interaction
combined with the feedback effect on the spin damping due to superconductivity
yields a Fermi-liquid form of the fermionic spectral function for where is the maximum value of the superconducting gap, and a
non-Fermi-liquid form for . In the Fermi-liquid regime,
the spectral function displays a quasiparticle peak at
; in the non-Fermi-liquid regime it possesses a broad
maximum (hump) at . In between the two regimes, the
spectral function has a dip at . We argue that our
theory also explains the tunneling data for the superconducting density of
states.Comment: 4 pages, RevTeX, 4 eps figures embedded in the tex
Renormalizacija tenzorske svojstvene energije u rezonantnoj kiralnoj teoriji
We study the problems related to the renormalization of propagators in resonance chiral theory, concentrating on the case of vector resonances in the antisymmetric tensor formalism. The general form of the propagators for antisymmetric tensor fields contains not only the resonance states but also the states that are ghosts or tachyons which decouple in the free-field limit. However, when the interaction terms are taking into account they are dynamically generated through the renormalization procedure.ProuÄavamo probleme oko renormalizacije propagatora u rezonantnoj kiralnoj teoriji, usredotoÄivĆĄi se na vektorske rezonancije u formalizmu antisimetriÄnih tenzora. OpÄi oblik propagatora antisimetriÄnih tenzorskih polja sadrĆŸi pored rezonantnih stanja i duhove i tahione koji se odvajaju u granici slobodnog polja. MeÄutim, ako se Älanovi meÄudjelovanja uzmu u obzir, oni se stvaraju dinamiÄki renormalizacijskim postupkom
Chiral expansions of the pi0 lifetime
The corrections induced by light quark masses to the current algebra result
for the lifetime are reexamined. We consider NNLO corrections and we
compute all the one-loop and the two-loop diagrams which contribute to the
decay amplitude at NNLO in the two-flavour chiral expansion. We show that the
result is renormalizable, as Weinberg consistency conditions are satisfied. We
find that chiral logarithms are present at this order unlike the case at NLO.
The result could be used in conjunction with lattice QCD simulations, the
feasibility of which was recently demonstrated. We discuss the matching between
the two-flavour and the three-flavour chiral expansions in the anomalous sector
at order one-loop and derive the relations between the coupling constants. A
modified chiral counting is proposed, in which counts as . We have
updated the various inputs needed and used this to make a phenomenological
prediction.Comment: 20 pages, 1 figure; v2: comments and references added, accepted for
publication in PR
The Effect of Disorder in an Orbitally Ordered Jahn-Teller Insulator
We study a two dimensional, two-band double-exchange model for
electrons coupled to Jahn-Teller distortions in the presence of quenched
disorder using a recently developed Monte-Carlo technique. In the absence of
disorder the half-filled system at low temperatures is an orbitally ordered
ferromagnetic insulator with a staggered pattern of Jahn-Teller distortions. We
examine the finite temperature transition to the orbitally disordered phase and
uncover a qualitative difference between the intermediate and strongly coupled
systems, including a thermally driven insulator to metal crossover in the
former case. Long range orbital order is suppressed in the presence of disorder
and the system displays a tendency towards metastable states consisting of
orbitally disordered stripe-like structures enclosing orbitally ordered
domains.Comment: 10 pages, 9 figure
Phase diagrams of Kitaev models for arbitrary magnetic field orientations
The Kitaev model is an exactly solvable quantum spin model within the language of constrained real fermions. In spite of numerous studies for magnetic fields along special orientations, there is a limited amount of knowledge on the complete field-angle characterization, which can provide valuable information on the existence of fractionalized excitations. For this purpose, we first study the pure ferromagnetic and antiferromagnetic Kitaev models for arbitrary external magnetic field directions via a mean-field theory, showing that there are many topological phases with different (or zero) Chern numbers, depending on the magnetic field strength and orientations. However, a realistic description of the candidate Kitaev materials, within the edge-sharing octahedra paradigm, requires additional coupling terms, including a large off-diagonal term Î along with possible anisotropic corrections Îp. It is therefore not sufficient to rely on the topological properties of the bare Kitaev model as the basis for the observed thermal Hall-conductivity signals, and an understanding of these extended Kitaev models with a complete field response is demanded. Starting from the zero-field phase diagram of KâÎâÎp models, we identify, besides the Kitaev spin liquid phase, antiferromagnetic zigzag, ferromagnetic phases, as well as an unusual Kitaev(-Î) spin liquid phase. The magnetic field response of these phases for arbitrary field orientations provides a remarkably rich phase diagram. For an extended parameter range and just above the critical field where the zigzag phase is suppressed, there is an intermediate phase region with suppressed energy gaps and substantial spin fractionalization. To comply our findings with experiments, we also reproduce a large asymmetry in the extent of this intermediate phases specifically for the two different field directions Ξ=±60o with respect to the normal to the plane of the honeycomb lattice
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