A hypothetical effect of the Maxwell-Proca electromagnetic stresses on galaxy rotation curves

The Maxwell-Proca electrodynamics corresponding to a finite photon mass causes a substantial change of the Maxwell stress tensor and, under certain circumstances, may cause the electromagnetic stresses to act effectively as "negative pressure." The paper describes a model where this negative pressure imitates gravitational pull and may produce forces comparable to gravity and even become dominant. The effect is associated with the random magnetic fields in the galactic disk with a scale exceeding the photon Compton wavelength. The presence of a weaker regular field does not affect the forces under consideration. The stresses act predominantly on the interstellar gas and cause an additional force pulling the gas towards the center and towards the galactic plane. The stars do not experience any significant direct force but get involved in this process via a "recycling loop" where rapidly evolving massive stars are formed from the gas undergoing galactic rotation and then lose their masses back to the gas within a time shorter than roughly 1/6 of the rotation period. This makes their dynamics inseparable from that of the rotating gas. The lighter, slowly evolving stars, as soon as they are formed, lose connection to the gas and are confined within the galaxy only gravitationally. Numerical examples based on the parameters of our galaxy reveal both opportunities and challenges of this model and motivate further analysis. The critical issue is the plausibility of formation of the irregular magnetic field that would be force free. Another challenge is developing a predictive model of the evolution of the gaseous and stellar population of the galaxy under the aforementioned scenario. It may be interesting to also explore possible broader cosmological implications of the negative-pressure model.Comment: 29 pages, 1 figur

Problems of the rotating-torsion-balance limit on the photon mass

We discuss the problems (and the promise) of the ingenious method introduced by Lakes, and recently improved on by Luo, to detect a possible small photon mass $\mu$ by measuring the ambient magnetic vector potential from large scale magnetic fields. We also point out how an improved ``indirect'' limit can be obtained using modern measurements of astrophysical magnetic fields and plasmas and that a good ``direct'' limit exists using properties of the solar wind.Comment: 4 pages, revised title and content

Effect of enhanced thermal dissipation on the Rayleigh-Taylor instability in emulsion-like media

Rayleigh-Taylor instability in a finely structured emulsion-like medium consisting of the two components of different compressibility is considered. Although the term ``emulsion`` is used to describe the structure of the medium, under typical fast Z-pinch conditions both components behave as gases. The two components are chosen in such a way that their densities in the unperturbed state are approximately equal. Specific emphasis has been made on the analysis of perturbations with the scale {lambda} considerably exceeding the size of the grains a. Averaged equations describing such perturbations am derived. The difference in compressibility of the two components leads to the formation of temperature variations at the scale a, and increases the rate of the thermal dissipation by a factor ({lambda}/a){sup 2}. The strongest stabilizing effect of the thermal dissipation takes place when the thermal relaxation time is comparable with the instability growth rate

Slow solitary waves in multi-layered magnetic structures

The propagation of slow sausage surface waves in a multi-layered magnetic configuration is considered. The magnetic configuration consists of a central magnetic slab sandwiched between two identical magnetic slabs (with equilibrium quantities different from those in the central slab) which in turn are embedded between two identical semi-infinite regions. The dispersion equation is obtained in the linear approximation. The nonlinear governing equation describing waves with a characteristic wavelength along the central slab much larger than the slab thickness is derived. Solitary wave solutions to this equation are obtained in the case where these solutions deviate only slightly from the algebraic soliton of the Benjamin-Ono equation

Some Physics Processes in the Nitrogen-Filled Photoluminescence Cell - Rev. 1

As shown in Ref. [1], the photoluminescence cell is a viable candidate for monitoring the total energy in the Linac Coherent Light Source. In Ref. [1], most of the discussion was concentrated on the cell with argon as a working gas. In the present note I provide a discussion of some physics processes that may affect the performance of the photoluminescence cell with the nitrogen fill. In particular, I will consider the role of the space charge effects, ambipolar diffusion, and recombination processes. This group of phenomena determines the duration of the afterglow process that follows an initial short (<100 ns) burst of optical radiation. The presence of this afterglow can be of some significance for the detection system. Compared to my previous note with the same title UCRL-TR-222274, a more detailed discussion of space charge effects is provided, with an emphasis on the electrostatic confinement of the primary electrons. Also, some additional atomic data are included into sections describing recombination processes. The general template for this discussion follows a draft report [1] where the argon-filled cell was considered. But some processes in nitrogen are different and require separate consideration. In what follows, I am not attempting to produce ''exact'' results, but rather to provide a quick order-of-magnitude scoping study

The LCLS Gas Attenuator Revisited

In the report ''X-ray attenuation cell'' [1] a preliminary analysis of the gas attenuator for the Linac Coherent Light Source (LCLS) was presented. This analysis was carried out for extremely stringent set of specifications. In particular, a very large diameter for the unobstructed beam was set (1 cm) to accommodate the spontaneous radiation; the attenuator was supposed to cover the whole range of energies of the coherent radiation, from 800 eV to 8000 eV; the maximum attenuation was set at the level of 10{sup 4}; the use of solid attenuators was not allowed, as well as the use of rotating shutters. The need to reach a sufficient absorption at the high-energy end of the spectrum predetermined the choice of Xe as the working gas (in order to have a reasonable absorption at a not-too-high pressure). A sophisticated differential pumping system that included a Penning-type ion pump was suggested in order to minimize the gas leak into the undulator/accelerator part of the facility. A high cost of xenon meant also that an efficient (and expensive) gas-recovery system would have to be installed. The main parameter that determined the high cost and the complexity of the system was a large radius of the orifice. The present viewpoint allows for much smaller size of the orifice, r{sub 0} = 1.5 mm. (1) The use of solid attenuators is also allowed (R.M. Bionta, private communication). It is, therefore, worthwhile to reconsider various parameters of the gas attenuator for these much less stringent conditions. This brief study should be considered as a physics input for the engineering design. As a working gas we consider now the argon, which, on the one hand, provides a reasonable absorption lengths and, on the other hand, is inexpensive enough to be exhausted into the atmosphere (no recovery). The absorption properties of argon are illustrated by Fig.1 where the attenuation factor A is shown for various beam energies, based on Ref. [2]. The other relevant parameters for argon are presented in Table 1

User facility for research on fusion systems with dense plasmas

There are a number of fusion systems whose dimensions can be scaled down to a few centimeters, if the plasma density and confining magnetic field are raised to sufficiently high values. This prompts a "user-facility" approach to the studies of this class of fusion systems. The concept of such a user facility was first briefly mentioned in Ref. 1. Here we present a more detailed description