The role of banks in the Brazilian interbank market: Does bank type matter?

This paper analyzes the Brazilian interbank network structure using a complex network-based approach. Results suggest a weak evidence of community structure, high heterogeneity of the network and that this market is characterized by money centers having exposures to many banks. Furthermore, we go beyond the structure of the network using information about the characteristics of the nodes and a non-parametric test in order to understand the role of the banks in the interbanking market.     

Is the efficiency of stock market correlated with multifractality? An evidence from the Shanghai stock market

In this paper, we propose an efficiency index and multifractality degree for financial markets, and investigate the dynamics of the relationship between the two indices for the Shanghai stock market employing the technique of rolling window. By using the DCCA cross-correlation coefficient, we find that, for the Shanghai stock market, the increase in the degree of market multifractality can lead to a lower degree of market efficiency before the equity division reforms, whereas it can result in a lower degree of market efficiency in the short-term and a higher degree of market efficiency in the long-term after the equity division reforms. This finding reflects the process of development of the Shanghai stock market and also provides strong evidence which supports Liu’s argument that the increase in the degree of market complexity can improve the market efficiency Liu (2009) [1].     

Does Basel II destabilize financial markets? An agent-based financial market perspective

We use a financial market model that is able to replicate stylized facts of financial markets quite successfully. We adjust this model by integrating regulations of Basel II concerning market risk. The result is a considerable destabilization of the regulated financial market with a significant increase of extreme events (extraordinary profits and losses). Since the intention of Basel II regulations is to ensure banks have enough regulatory capital to withstand periods involving extraordinary losses, it is alarming that – on the contrary – these regulations may provoke an increase in precisely such extraordinary events.     

Does the electron have a structure?

... it ain't likely to have a radius of exactly zero, is the conclusion of H. G. Dehmelt⁽¹⁾ from his Nobel Prize (1989) winning observations on trapped electrons. There are small discrepancies between Dehmelt's observations and the theoretical predictions of quantum electrodynamics (QED), which assumes that the electron is a point particle. Here we present evidence in support of Dehmelt's contention that the electron has a structure. Essentially, we point out that the nonrelativistic limit of QED is at variance with a fundamental principle underlying all of physics, viz. the second law of thermodynamics.     

Does the Gaussian thermostat maximize the phase-space compression factor?

A recent hypothesis of D. J. Evans and A. Baranyai according to which the Gaussian thermostat maximizes the average phase-space compression factor in nonequilibrium steady states is analyzed for a dilute gas under uniform shear flow. Three routes have been followed: (i) an exact solution of the Bhatnagar-Gross-Krook kinetic equation for arbitrary shear rate, (ii) an exact solution of the Boltzmann equation through super-Burnett order, and (iii) a numerical solution of the Boltzmann equation for finite shear rates. The results show that the above hypothesis does not exactly hold for arbitrary shear rates, although the thermostat that maximizes is close to the Gaussian one. In addition, the influence of the thermostat considered on the nonlinear shear viscosity is also analyzed.     

Does the planck mass run on the cosmological-horizon scale?

Einstein's theory of general relativity contains a universal value of the Planck mass. However, one may envisage that in alternative theories of gravity the effective value of the Planck mass (or Newton's constant), which quantifies the coupling of matter to metric perturbations, can run on the cosmological-horizon scale. In this Letter, we study the consequences of a glitch in the Planck mass from subhorizon to superhorizon scales. We show that current cosmological observations severely constrain this glitch to less than 1.2%.     

Does the interface experience the van der Waals loop?

A discussion is given of the role of the unstable and metastable parts (the loop) in the equation of state of the van der Waals or Landau type for the interface theory. The role of the loop in the field-theoretic renormalization calculation of the interface is analyzed. It is shown that in real-space renormalization no loop occurs and that a satisfactory interface calculation can be made using Migdal's renormalization procedure.     

Does proton decay follow the exponential law?

Tetrads cause the breakdown of symmetry in gravitational theories. Their vacuum expected values reduce the symmetry of the vacuum from that of the action to what is global Poincaré invariance at ordinary distances. Gravitational theories can be written in terms of rescaled fields in such a way that the Planck mass never appears. The rescaled fields are dimensionless, except for gauge fields and tetrads, both of which acquire the dimension of mass. The empirical distribution of energy throughout spacetime causes the tetrads to assume vacuum expected values of the order of the Planck mass,m _p . Thus the gravitational constant,G=hc/m _p ² , may be viewed not as a fundamental constant, but as a mass scale that is dynamically determined by the large-scale structure of the universe. Generalized tetrads may also break internal symmetries.     

Does the glory have a simple explanation?

The explanation for the meteorological glory provided by the complex angular momentum theory is revisited in response to comments that a simpler physical picture would be desirable. New results that confirm the tunneling origin of the glory and the roles of resonances and surface waves in this phenomenon are presented, and expressions for averaged angular distribution and polarization features are given.     

Does the Aharonov–Bohm Effect Exist?

We draw a distinction between the Aharonov–Bohm phase shift and the Aharonov–Bohm effect. Although the Aharonov–Bohm phase shift occurring when an electron beam passes around a magnetic solenoid is well-verified experimentally, it is not clear whether this phase shift occurs because of classical forces or because of a topological effect occurring in the absence of classical forces as claimed by Aharonov and Bohm. The mathematics of the Schroedinger equation itself does not reveal the physical basis for the effect. However, the experimentally observed Aharonov–Bohm phase shift is of the same form as the shift observed due to electrostatic forces for which the consensus view accepts the role of the classical forces. The Aharonov–Bohm phase shift may well arise from classical electromagnetic forces which are simply more subtle in the magnetic case since they involve relativistic effects of the order v ² /c ² . Here we first review the experimentally observable differences between phenomena arising from classical forces and phenomena arising from the quantum topological effect suggested by Aharonov and Bohm. Second we point out that most discussions of the classical electromagnetic forces involved when a charged particle passes a solenoid are inaccurate because they omit the Faraday induction terms. The subtleties of the relativisitic v ² /c ² classical electromagnetic forces between a point charge and a solenoid have been explored by Coleman and Van Vleck in their analysis of the Shockley–James paradox; indeed, we point out that an analysis exactly parallel to that of Coleman and Van Vleck suggests that the Aharonov–Bohm phase shift is actually due to classical electromagnetic forces. Finally we note that electromagnetic velocity fields penetrate even excellent conductors in a form which is unfamiliar to many physicists. An ohmic conductor surrounding a solenoid does not screen out the magnetic field of the passing charge, but rather the time-integral of the magnetic field is an invariant; this time integral is precisely what is involved in the classical explanation of the Aharonov–Bohm phase shift. Thus the persistence of the Aharonov–Bohm phase shift when the solenoid is surrounded by a conductor does not exclude a classical force-based explanation for the phase shift. At present there is no experimental evidence for the Aharonov–Bohm effect.     

How Does an Electron Tell the Time?

We examine a model of a digital clock to clarify the origin of the spacetime approach in special relativity. Specifically, we consider a two photon clock and assemble a statistical mechanics of such clocks to see how Minkowski space relates to local finite frequency clock behaviour. The result suggests that finite frequency clocks measure spacetime area and it is this feature that provides a simple mechanism behind Minkowski space on large scales. The same feature appears to implicate quantum mechanics on small scales.     

Why Does the Geometric Product Simplify the Equations of Physics?

In the last decades it was observed that Clifford algebras and geometric product provide a model for different physical phenomena. We propose an explanation of this observation based on the theory of bounded symmetric domains and the algebraic structure associated with them. The invariance of physical laws is a result of symmetry of the physical world that is often expressed by the symmetry of the state space for the system implying that this state space is a symmetric domain. For example, the ball of all possible velocities is a bounded symmetric domain. The symmetry on this ball follow from the symmetry of the space-time transformations between two inertial systems, which fixes the so-called symmetric velocity between them. The Lorenz transformations acts on the ball Sof symmetric velocities by conformal transformations. The ball Sis a spin ball (type IV in Cartan's classification). The Lie algebra of this ball is defined a triple product that is closely related to geometric product. The relativistic dynamic equations in mechanics and for the Lorenz force is described by this Lie algebra and the triple product.     

Does the entropy of the Universe tend to a maximum?

Ordinary, macroscopic systems, naturally tend to a state of maximum entropy compatible with their constraints. However, this might not hold for gravity-dominated systems since their entropy may increase without bound unless this is precluded by the formation of a black hole. In this short note we suggest, based on the Hubble expansion history, that our Universe likely behaves as an ordinary system, i.e., that its entropy seems to tend to some maximum value.     

Does the multiple-scattering series in the pion-deuteron scattering actually converge?

It is demonstrated that the well-known answer for the multiple-scattering series (MSS) for a light particle interacting to a pair of static nucleons, calculated in the Fixed Centers Approximation (FCA), works well for a wide region of the two-body complex scattering length a. However, this approach is not applicable in a narrow region surrounding the real positive a half-axis, where the MSS does not converge. Simultaneously, for real positive a’s the 3-body system forms an infinite set of bound states.     

Does Charge Contribute to the Frame Dragging of?Spacetime?

Electrically charged systems bound by a strong gravitational force can sustain a huge amount of electric charge (up to 10²⁰ C) against Coulomb repulsion. General relativistically such systems form a stable hydrostatic configuration both in the non-rotating and rotating cases. Here we study the effects of electric charge (electric energy density) on the spacetime outside a rotating electrically charged system bound by a strong gravitational force. In particular we investigate the effect of charge density on frame-dragging of spacetime in the exterior region. Using the coupled Einstein-Maxwell equations it is found that in the slow rotation approximation charge accumulation not only acts like an additional mass, thus modifying the spherically symmetric part of the spacetime, the electric charge also contributes directly to the dragging of spacetime. A modified Lense-Thirring formula for the spacetime frame dragging frequency is obtained and its implication for rotating charged compact stars is discussed.