70 research outputs found
The Distributional Implications of a Carbon Tax in Ireland. ESRI WP250. July 2008
We study the effects of carbon tax and revenue recycling across the income distribution in the Republic of Ireland. In absolute terms, a carbon tax of €20/tCO2 would cost the poorest households less than €3/week and the richest households more than €4/week. A carbon tax is regressive, therefore. However, if the tax revenue is used to increase social benefits and tax credits, households across the income distribution can be made better off without exhausting the total carbon tax revenue
On the spectral density from instantons in quenched QCD
We investigate the contribution of instantons to the eigenvalue spectrum of
the Dirac operator in quenched QCD. The instanton configurations that we use
have been derived, elsewhere, from cooled SU(3) lattice gauge fields and, for
comparison, we also analyse a random `gas' of instantons. Using a set of
simplifying approximations, we find a non-zero chiral condensate. However we
also find that the spectral density diverges for small eigenvalues, so that the
chiral condensate, at zero quark mass, diverges in quenched QCD. The degree of
divergence decreases with the instanton density, so that it is negligible for
the smallest number of cooling sweeps but becomes substantial for larger number
of cools. We show that the spectral density scales, that finite volume
corrections are small and we see evidence for the screening of topological
charges. However we also find that the spectral density and chiral condensate
vary rapidly with the number of cooling sweeps -- unlike, for example, the
topological susceptibility. Whether the problem lies with the cooling or with
the identification of the topological charges is an open question. This problem
needs to be resolved before one can determine how important is the divergence
we have found for quenched QCD.Comment: 33 pages, 16 figures (RevTex), substantial revisions; to appear in
Phys.Rev.
Analysis of the vector form factors and with light-cone QCD sum rules
In this article, we calculate the vector form factors and
within the framework of the light-cone QCD sum rules
approach. The numerical values of the are compatible with the
existing theoretical calculations, the central value of the ,
, is in excellent agreement with the values from the chiral
perturbation theory and lattice QCD. The values of the are
very large comparing with the theoretical calculations and experimental data,
and can not give any reliable predictions. At large momentum transfers with
, the form factors and can
either take up the asymptotic behavior of or decrease more
quickly than , more experimental data are needed to select the
ideal sum rules.Comment: 22 pages, 16 figures, revised version, to appear in Eur. Phys. J.
Duality Versus Supersymmetry and Compactification
We study the interplay between T-duality, compactification and supersymmetry.
We prove that when the original configuration has unbroken space-time
supersymmetries, the dual configuration also does if a special condition is
met: the Killing spinors of the original configuration have to be independent
on the coordinate which corresponds to the isometry direction of the bosonic
fields used for duality. Examples of ``losers" (T-duals are not supersymmetric)
and ``winners" (T-duals are supersymmetric) are given.Comment: LaTeX file, 19 pages, U. of Groningen Report UG-8/94, Stanford U.
Report SU-ITP-94-19, QMW College Report QMW-PH-94-1
The Study of Goldstone Modes in =2 Bilayer Quantum Hall Systems
At the filling factor =2, the bilayer quantum Hall system has three
phases, the spin-ferromagnet phase, the spin singlet phase and the canted
antiferromagnet (CAF) phase, depending on the relative strength between the
Zeeman energy and interlayer tunneling energy. We present a systematic method
to derive the effective Hamiltonian for the Goldstone modes in these three
phases. We then investigate the dispersion relations and the coherence lengths
of the Goldstone modes. To explore a possible emergence of the interlayer phase
coherence, we analyze the dispersion relations in the zero tunneling energy
limit. We find one gapless mode with the linear dispersion relation in the CAF
phase.Comment: 13 pages, no figures. One reference is added. Typos correcte
(Non) singular Kantowski-Sachs Universe from quantum spherically reduced matter
Using s-wave and large N approximation the one-loop effective action for 2d
dilaton coupled scalars and spinors which are obtained by spherical reduction
of 4d minimal matter is found. Quantum effective equations for reduced Einstein
gravity are written. Their analytical solutions corresponding to 4d
Kantowski-Sachs (KS) Universe are presented. For quantum-corrected Einstein
gravity we get non-singular KS cosmology which represents 1) quantum-corrected
KS cosmology which existed on classical level or 2)purely quantum solution
which had no classical limit. The analogy with Nariai BH is briefly mentioned.
For purely induced gravity (no Einstein term) we found general analytical
solution but all KS cosmologies under discussion are singular. The
corresponding equations of motion are reformulated as classical mechanics
problem of motion of unit mass particle in some potential V.Comment: LaTeX file, 16 pages, a few misprints are correcte
Singularities In Scalar-Tensor Cosmologies
In this article, we examine the possibility that there exist special
scalar-tensor theories of gravity with completely nonsingular FRW solutions.
Our investigation in fact shows that while most probes living in such a
Universe never see the singularity, gravity waves always do. This is because
they couple to both the metric and the scalar field, in a way which effectively
forces them to move along null geodesics of the Einstein conformal frame. Since
the metric of the Einstein conformal frame is always singular for
configurations where matter satisfies the energy conditions, the gravity wave
world lines are past inextendable beyond the Einstein frame singularity, and
hence the geometry is still incomplete, and thus singular. We conclude that the
singularity cannot be entirely removed, but only be made invisible to most, but
not all, probes in the theory.Comment: 23 pages, latex, no figure
Exploring skewed parton distributions with two body models on the light front II: covariant Bethe-Salpeter approach
We explore skewed parton distributions for two-body, light-front wave
functions. In order to access all kinematical regimes, we adopt a covariant
Bethe-Salpeter approach, which makes use of the underlying equation of motion
(here the Weinberg equation) and its Green's function. Such an approach allows
for the consistent treatment of the non-wave function vertex (but rules out the
case of phenomenological wave functions derived from ad hoc potentials). Our
investigation centers around checking internal consistency by demonstrating
time-reversal invariance and continuity between valence and non-valence
regimes. We derive our expressions by assuming the effective qq potential is
independent of the mass squared, and verify the sum rule in a non-relativistic
approximation in which the potential is energy independent. We consider
bare-coupling as well as interacting skewed parton distributions and develop
approximations for the Green's function which preserve the general properties
of these distributions. Lastly we apply our approach to time-like form factors
and find similar expressions for the related generalized distribution
amplitudes.Comment: 25 pages, 12 figures, revised (minor changes but essential to
consistency
Modeling quark-hadron duality for relativistic, confined fermions
We discuss a model for the study of quark-hadron duality in inclusive
electron scattering based on solving the Dirac equation numerically for a
scalar confining linear potential and a vector color Coulomb potential. We
qualitatively reproduce the features of quark-hadron duality for all potentials
considered, and discuss similarities and differences to previous models that
simplified the situation by treating either the quarks or all particles as
scalars. We discuss the scaling results for PWIA and FSI, and the approach to
scaling using the analog of the Callan-Gross relation for y-scaling.Comment: 38 pages, 21 figure
Light-Front Approach for Heavy Pentaquark Transitions
Assuming the two diquark structure for the pentaquark state as advocated in
the Jaffe-Wilczek model, there exist exotic parity-even anti-sextet and
parity-odd triplet heavy pentaquark baryons. The theoretical estimate of
charmed and bottom pentaquark masses is quite controversial and it is not clear
whether the ground-state heavy pentaquark lies above or below the strong-decay
threshold. We study the weak transitions of heavy pentaquark states using the
light-front quark model. In the heavy quark limit, heavy-to-heavy pentaquark
transition form factors can be expressed in terms of three Isgur-Wise
functions: two of them are found to be normalized to unity at zero recoil,
while the third one is equal to 1/2 at the maximum momentum transfer, in
accordance with the prediction of the large-Nc approach or the quark model.
Therefore, the light-front model calculations are consistent with the
requirement of heavy quark symmetry. Numerical results for form factors and
Isgur-Wise functions are presented. Decay rates of the weak decays Theta_b+ to
Theta_c0 pi+ (rho+), Theta_c0 to Theta+ pi- (rho-), Sigma'_{5b}+ to
Sigma'_{5c}0 pi+ (rho+) and Sigma'_{5c}0 to N_8+ pi- (rho-) with Theta_Q,
Sigma'_{5Q} and N_8 being the heavy anti-sextet, heavy triplet and light
octet pentaquarks, respectively, are obtained. For weakly decaying Theta_b+ and
Theta_c0, the branching ratios of Theta_b+ to Theta_c0 pi+, Theta_c0 to Theta+
pi- are estimated to be at the level of 10^{-3} and a few percents,
respectively.Comment: 33 pages, 3 figures, version to be published in Phys. Rev.
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