29,195 research outputs found
The Role of Fermions in Bubble Nucleation
We present a study of the role of fermions in the decay of metastable states
of a scalar field via bubble nucleation. We analyze both one and
three-dimensional systems by using a gradient expansion for the calculation of
the fermionic determinant. The results of the one-dimensional case are compared
to the exact results of previous work.Comment: 15 pages, revtex, 9 figure
Absence of Gluonic Components in Axial and Tensor Mesons
A quarkonium-gluonium mixing scheme previously developed to describe the
characteristic of the pseudoscalar mesons is applied to axial and tensor
mesons. The parameters of the model are determined by fitting the eigenvalues
of a mass matrix. The corresponding eigenvectors give the proportion of light
quarks, strange quarks and glueball in each meson. However the predictions of
the model for branching ratios and electromagnetic decays are incompatible with
the experimental results. These results suggest the absence of gluonic
components in the states of axial and tensor isosinglet mesons analyzed here.Comment: 12 page
Comment on Market Discipline and Monetary Policy by Carl Walsh
This paper aims at correcting flaws in the way expectations are set in a paper by Walsh (2000) in order to assess with precision the impact of complex market rigidities and market expectations in the optimal choices of inflation in a monetary game between society and central bankers. After setting the expectations right, one of the results achieved indicates that the optimal inflation under any type of central banker is higher than that obtained in the original paper, suggesting that the time inconsistency phenomenon plays a more important role in explaining an inflationary bias than originally interpreted by Walsh (2000). However, if society organizes itself towards shorter tenure wage contracts, inflation will be lower. The results obtained for the output gap of the economy also differ from those achieved by Walsh in the sense that a central banker who is highly committed to previously announced inflation targets will have more opportunities to generate output growth above equilibrium rates and still commit. Finally, the stability of the premises regarding the contractual structure of the economy proposed by Walsh is tested under a game theoretic approach. The outcome of the test is that stability can be guaranteed only under strong assumptions and high symmetry in the sectoral distribution of firms. By using a social welfare function in which price surprises in any direction lead to welfare loss, the results indicate that society is better off by choosing longer tenure wage contracts, moving away from shorter tenure ones, at the cost of higher inflation.
Uniform semiclassical approximation in quantum statistical mechanics
We present a simple method to deal with caustics in the semiclassical
approximation to the partition function of a one-dimensional quantum system.
The procedure, which makes use of complex trajectories, is applied to the
quartic double-well potential.Comment: 5 pages, 1 figure, Latex. Contribution to the Proceedings of the XXI
Brazilian National Meeting on Particles and Fields (Sao Lourenco, October
23-27, 2000
Quantum statistical correlations in thermal field theories: boundary effective theory
We show that the one-loop effective action at finite temperature for a scalar
field with quartic interaction has the same renormalized expression as at zero
temperature if written in terms of a certain classical field , and if
we trade free propagators at zero temperature for their finite-temperature
counterparts. The result follows if we write the partition function as an
integral over field eigenstates (boundary fields) of the density matrix element
in the functional Schr\"{o}dinger field-representation, and perform a
semiclassical expansion in two steps: first, we integrate around the
saddle-point for fixed boundary fields, which is the classical field ,
a functional of the boundary fields; then, we perform a saddle-point
integration over the boundary fields, whose correlations characterize the
thermal properties of the system. This procedure provides a
dimensionally-reduced effective theory for the thermal system. We calculate the
two-point correlation as an example.Comment: 13 pages, 1 figur
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