On the production of heavy axion-like particles in the accretion disks of gamma-ray bursts

Heavy axion-like particles have been introduced in several scenarios beyond the Standard Model and their production in some astrophysical systems should be possible. In this work, we re-examine the possibility that these type of particles can be generated in the accretion disks of gamma-ray bursts (GRB), the most powerful events in the universe. If the produced axions decay into photons or $e^+e-$ pairs at the correct distances, a fireball is generated. We calculate the structure transient accretion disks in GRBs (density, temperature and thickness profiles) taking into account the effect of heavy axion emission as well as the rest of the relevant standard cooling processes. This allows us to obtain the values of the coupling constant g_{aN} in order for the axions not to become trapped, and we can also compute the emitted heavy axion luminosity from the entire disk. We find that for the couplings within the ranges found, then the mechanism for powering GRBs based on heavy axion production and decay becomes an alternative to the standard picture based upon magnetohydrodynamic processes and neutrino-antineutrino annihilation. Otherwise, if heavy axions are produced in the disk but their decay to takes place further away, the mechanism fails. Still, the decay products (gamma rays or electrons and positrons) should leave observable signatures which are not observed for different ranges of values of the coupling constants, depending on the mass of the heavy axionComment: 14 pages, 7 figures. Updated version that matches the one to be published on Physics Letters

Can subsidiaries of foreign banks contribute to the stability of the Forex market in Emerging Economies?

Over the last decade, the ownership of the banking sector in Latin America has changed hands from local shareholders to large foreign banks from Spain and the United States. It is also a fact that the foreign exchange market in these countries has been segmented through various kinds of restrictions, because the central bank is unable to function as a lender of last resort in a currency other than its own. The standing issue is whether in practice, a parent bank effectively takes the role of such lender of last resort in supporting its subsidiaries overseas. If that were to be the case, the question is if having a significant participation of foreign subsidiaries is a necessary condition for lifting such restrictions. The data on the compliance of domestic and foreign banks with the dollar reserve requirements in Mexico is used to try to address this question. The answer is a qualified yes. When there are weak domestic banks, it seems that subsidiaries fo foreign banks have a better access to funding in foreign exchange, specially in times of stress. However, when compared with strong domestic banks, the evidence suggests that these local entities can do as well or even better than the foreign subsidiaries.

A two-zone approach to neutrino production in gamma-ray bursts

Gamma-ray bursts (GRB) are the most powerful events in the universe. They are capable of accelerating particles to very high energies, so are strong candidates as sources of detectable astrophysical neutrinos. We study the effects of particle acceleration and escape by implementing a two-zone model in order to assess the production of high-energy neutrinos in GRBs associated with their prompt emission. Both primary relativistic electrons and protons are injected in a zone where an acceleration mechanism operates and dominates over the losses. The escaping particles are re-injected in a cooling zone that propagates downstream. The synchrotron photons emitted by the accelerated electrons are taken as targets for $p\gamma$ interactions, which generate pions along with the $pp$ collisions with cold protons in the flow. The distribution of these secondary pions and the decaying muons are also computed in both zones, from which the neutrino output is obtained. We find that for escape rates lower than the acceleration rate, the synchrotron emission from electrons in the acceleration zone can account for the GRB emission, and the production of neutrinos via $p\gamma$ interactions in this zone becomes dominant for $E_\nu>10^5$ GeV. For illustration, we compute the corresponding diffuse neutrino flux under different assumptions and show that it can reach the level of the signal recently detected by IceCube.Comment: 11 pages, 7 figures, to appear in A&

Using Signal Processing Tools for Regulation Analysis and Implementation

Regulators often face the challenge of designing and implementing rules that both, respond to the policy objectives and that can be clearly referred to the day-to-day operations and practices in the marketplace. In many cases, the actual codes end up being a cumbersome collection of conditions that are very difficult to evaluate and re-design. This paper suggests that some of the most commonly used tools in Signal Processing could offer a convenient vehicle for tackling these difficulties. By starting from a SIMULINK(R) model of the regulation of Banco de Mexico on the foreign exchange transactions of commercial banks, this paper offers an example of how those tools could be used in this context.

On the Effects of Regulation-Induced Forex Market Segmentation in Small Open Economies

The central banks of small open economies have to procure the proper operation of the payments system for transactions with the rest of the world. They do so facing the constraint of a limited stock of international reserves. To make ends meet, they usually rely on three instruments: the choice of an exchange rate regime, the regulation of the foreign exchange transactions of commercial banks and general exchange controls. Based on some stylized facts of the Mexican experience of the past three decades, this paper uses a SIMULINK(R) model to show the effects of different institutional constructs on some key nominal variables. For a reasonable set of simulation parameters, it shows that either the complete segmentation of the peso-dollar market or a full integration of both markets are preferable to intermediate arrangements that contemplate some form of partial financial liberalization.

Can Subsidiaries of Foreign Banks Contribute to the Stability of the Forex Market in Emerging Economies? A Look at Some Evidence from the Mexican...

Over the last decade, the ownership of the banking sector in Latin America has changed hands from local shareholders to large foreign banks from Spain and the United States. It is also a fact that the foreign exchange market in these countries has been segmented through various kinds of restrictions, because the central bank is unable to function as a lender of last resort in a currency other than its own. The standing issue is whether in practice, a parent bank effectively takes the role of such lender of last resort in supporting its subsidiaries overseas. If that were to be the case, the question is if having a significant participation of foreign subsidiaries is a necessary condition for lifting such restrictions. The data on the compliance of domestic and foreign banks with the dollar reserve requirements in Mexico is used to try to address this question. The answer is a qualified yes. When there are weak domestic banks, it seems that subsidiaries of foreign banks have a better access to funding in foreign exchange, specially in times of stress. However, when compared with strong domestic banks, the evidence suggests that these local entities can do as well or even better than the foreign subsidiaries.