1,135 research outputs found
Matching functions for heavy particles
We introduce matching functions as a means of summing heavy-quark logarithms
to any order. Our analysis is based on Witten's approach, where heavy quarks
are decoupled one at a time in a mass-independent renormalization scheme. The
outcome is a generalization of the matching conditions of Bernreuther and
Wetzel: we show how to derive closed formulas for summed logarithms to any
order, and present explicit expressions for leading order and next-to-leading
order contributions. The decoupling of heavy quarks in theories lacking
asymptotic freedom is also considered.Comment: Revised version to be published in Physical Review D; added section
with application to decoupling of heavy particles in non-asymptotically free
theorie
Finite size scaling in the 2D XY-model and generalized universality
In recent works (BHP), a generalized universality has been proposed, linking
phenomena as dissimilar as 2D magnetism and turbulence. To test these ideas, we
performed a MC study of the 2D XY-model. We found that the shape of the
probability distribution function for the magnetization M is non Gaussian and
independent of the system size --in the range of the lattice sizes studied--
below the Kosterlitz-Thoules temperature. However, the shape of these
distributions does depend on the temperature, contrarily to the BHP's claim.
This behavior is successfully explained by using an extended finite-size
scaling analysis and the existence of bounds for M.Comment: 7 pages, 5 figures. Submitted to Phys. Rev. Lett. Details of changes:
1. We emphasized in the abstract the range of validity of our results. 2. In
the last paragraph the temperature dependence of the PDF was slightly
re-formulate
Dynamics of false vacuum bubbles in Brans-Dicke theory
We study the dynamics of false vacuum bubbles in the Brans-Dicke theory of
gravity by using the thin shell or thin wall approximation. We consider a false
vacuum bubble that has a different value for the Brans-Dicke field between the
inside false vacuum region and the outside true vacuum region. Within a certain
limit of field values, the difference of field values makes the effective
tension of the shell negative. This allows new expanding false vacuum bubbles
to be seen by the outside observer, which are disallowed in Einstein gravity.Comment: 29 pages, 20 figure
Stochastic magnetohydrodynamic turbulence in space dimensions
Interplay of kinematic and magnetic forcing in a model of a conducting fluid
with randomly driven magnetohydrodynamic equations has been studied in space
dimensions by means of the renormalization group. A perturbative
expansion scheme, parameters of which are the deviation of the spatial
dimension from two and the deviation of the exponent of the powerlike
correlation function of random forcing from its critical value, has been used
in one-loop approximation. Additional divergences have been taken into account
which arise at two dimensions and have been inconsistently treated in earlier
investigations of the model. It is shown that in spite of the additional
divergences the kinetic fixed point associated with the Kolmogorov scaling
regime remains stable for all space dimensions for rapidly enough
falling off correlations of the magnetic forcing. A scaling regime driven by
thermal fluctuations of the velocity field has been identified and analyzed.
The absence of a scaling regime near two dimensions driven by the fluctuations
of the magnetic field has been confirmed. A new renormalization scheme has been
put forward and numerically investigated to interpolate between the
expansion and the double expansion.Comment: 12 pages, 4 figure
Critical scaling of the a.c. conductivity for a superconductor above Tc
We consider the effects of critical superconducting fluctuations on the
scaling of the linear a.c. conductivity, \sigma(\omega), of a bulk
superconductor slightly above Tc in zero applied magnetic field. The dynamic
renormalization- group method is applied to the relaxational time-dependent
Ginzburg-Landau model of superconductivity, with \sigma(\omega) calculated via
the Kubo formula to O(\epsilon^{2}) in the \epsilon = 4 - d expansion. The
critical dynamics are governed by the relaxational XY-model
renormalization-group fixed point. The scaling hypothesis \sigma(\omega) \sim
\xi^{2-d+z} S(\omega \xi^{z}) proposed by Fisher, Fisher and Huse is explicitly
verified, with the dynamic exponent z \approx 2.015, the value expected for the
d=3 relaxational XY-model. The universal scaling function S(y) is computed and
shown to deviate only slightly from its Gaussian form, calculated earlier. The
present theory is compared with experimental measurements of the a.c.
conductivity of YBCO near Tc, and the implications of this theory for such
experiments is discussed.Comment: 16 pages, submitted to Phys. Rev.
Coordinate Representation of the One-Spinon One-Holon Wavefunction and Spinon-Holon Interaction
By deriving and studying the coordinate representation for the one-spinon
one-holon wavefunction we show that spinons and holons in the supersymmetric model with interaction attract each other. The interaction causes
a probability enhancement in the one-spinon one-holon wavefunction at short
separation between the particles. We express the hole spectral function for a
finite lattice in terms of the probability enhancement, given by the one-spinon
one-holon wavefunction at zero separation. In the thermodynamic limit, the
spinon-holon attraction turns into the square-root divergence in the hole
spectral function.Comment: 20 pages, 3 .eps figure
A new non-Fermi liquid fixed point
We study a new exchange interaction in which the conduction electrons with
pseudo spin interact with the impurity spin . Due to the
overscreening of the impurity spin by higher conduction electron spin, a new
non-trivial intermediate coupling strength fixed point is realized. Using the
numerical renormalization group (NRG), we show that the low-energy spectra are
described by a non-Fermi liquid excitation spectrum. A conformal field theory
analysis is compared with NRG results and excellent agreement is obtained.
Using the double fusion rule to generate the operator spectrum with the
conformal theory, we find that the specific heat coefficient and magnetic
susceptibility will diverge as , that the scaling dimension of an
applied magnetic field is , and that exchange anisotropy is always
relevant. We discuss the possible relevance of our work to two-level system
Kondo materials and dilute cerium alloys, and we point out a paradox in
understanding the Bethe-Ansatz solutions to the multichannel Kondo model.Comment: Revised. 20 page
Hidden non-Fermi liquid behavior due to crystal field quartet
We study a realistic Kondo model for crystal field quartet ground states
having magnetic and non-magnetic (quadrupolar) exchange couplings with
conduction electrons, using the numerical renormalization group method. We
focus on a local effect dependent on singlet excited states coupled to the
quartet, which reduces the non-magnetic coupling significantly and drives
non-Fermi liquid behavior observed in the calculated quadrupolar
susceptibility. A crossover from the non-Fermi liquid state to the Fermi liquid
state is characterized by a small energy scale very sensitive to the
non-magnetic coupling. On the other hand, the Kondo temperature observed in the
magnetic susceptibility is less sensitive. The different crystal-field
dependence of the two exchange couplings may be related to the different
dependence of quadrupolar and magnetic ordering temperatures in
CeLaB.Comment: 7 pages, 5 EPS figures, REVTe
Decay constants, light quark masses and quark mass bounds from light quark pseudoscalar sum rules
The flavor and pseudoscalar correlators are investigated using
families of finite energy sum rules (FESR's) known to be very accurately
satisfied in the isovector vector channel. It is shown that the combination of
constraints provided by the full set of these sum rules is sufficiently strong
to allow determination of both the light quark mass combinations ,
and the decay constants of the first excited pseudoscalar mesons in
these channels. The resulting masses and decay constants are also shown to
produce well-satisfied Borel transformed sum rules, thus providing non-trivial
constraints on the treatment of direct instanton effects in the FESR analysis.
The values of and obtained are in good agreement with the
values implied by recent hadronic decay analyses and the ratios obtained
from ChPT. New light quark mass bounds based on FESR's involving weight
functions which strongly suppress spectral contributions from the excited
resonance region are also presented.Comment: 28 pages, 10 figure
Magnetic Oscillations in Dense Cold Quark Matter with Four-Fermion Interactions
The phase structures of Nambu-Jona-Lasinio models with one or two flavours
have been investigated at non-zero values of and , where is an
external magnetic field and is the chemical potential. In the phase
portraits of both models there arise infinitely many massless chirally
symmetric phases, as well as massive ones with spontaneously broken chiral
invariance, reflecting the existence of infinitely many Landau levels. Phase
transitions of first and second orders and a lot of tricritical points have
been shown to exist in phase diagrams. In the massless case, such a phase
structure leads unavoidably to the standard van Alphen-de Haas magnetic
oscillations of some thermodynamical quantities, including magnetization,
pressure and particle density. In the massive case we have found an oscillating
behaviour not only for thermodynamical quantities, but also for a dynamical
quantity as the quark mass. Besides, in this case we have non-standard, i.e.
non-periodic, magnetic oscillations, since the frequency of oscillations is an
-dependent quantity.Comment: latex, 29 pages, 8 figure
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