36,131 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
Coexistence of -loop-current order with checkerboard d-wave CDW/PDW order in a hot-spot model for cuprate superconductors
We investigate the strong influence of the -loop-current order
on both unidirectional and bidirectional d-wave
charge-density-wave/pair-density-wave (CDW/PDW) composite orders along axial
momenta and that emerge in an effective hot spot
model departing from the three-band Emery model relevant to the phenomenology
of the cuprate superconductors. This study is motivated by the compelling
evidence that the -loop-current order described by this model may
explain groundbreaking experiments such as spin-polarized neutron scattering
performed in these materials. Here, we demonstrate, within a saddle-point
approximation, that the -loop-current order clearly coexists with
bidirectional (i.e. checkerboard) d-wave CDW and PDW orders along axial
momenta, but is visibly detrimental to the unidirectional (i.e. stripe) case.
This result has potentially far-reaching implications for the physics of the
cuprates and agrees well with very recent x-ray experiments on YBCO that
indicate that at higher dopings the CDW order has indeed a tendency to be
bidirectional.Comment: Published in Physical Review
Optimal network topologies for information transmission in active networks
This work clarifies the relation between network circuit (topology) and
behavior (information transmission and synchronization) in active networks,
e.g. neural networks. As an application, we show how to determine a network
topology that is optimal for information transmission. By optimal, we mean that
the network is able to transmit a large amount of information, it possesses a
large number of communication channels, and it is robust under large variations
of the network coupling configuration. This theoretical approach is general and
does not depend on the particular dynamic of the elements forming the network,
since the network topology can be determined by finding a Laplacian matrix (the
matrix that describes the connections and the coupling strengths among the
elements) whose eigenvalues satisfy some special conditions. To illustrate our
ideas and theoretical approaches, we use neural networks of electrically
connected chaotic Hindmarsh-Rose neurons.Comment: 20 pages, 12 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.
Holonomy Transformation in the FRW Metric
In this work we investigate loop variables in Friedman-Robertson-Walker
spacetime. We analyze the parallel transport of vectors and spinors in several
paths in this spacetime in order to classify its global properties. The band
holonomy invariance is analysed in this background.Comment: 8 page
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