Large-scale filaments--Newtonian vs. modified dynamics

Eisenstein Loeb and Turner (ELT) have recently proposed a method for estimating the dynamical masses of large-scale filaments, whereby the filament is modeled by an axisymmetric, isothermal cylinder, for which ELT derive a global relation between the (constant) velocity dispersion and the total line density. We first show that the model assumptions of ELT can be relaxed materially: an exact relation between the velocity and line density is derived for any cylinder (not necessarily axisymmetric), with an arbitrary constituent distribution function (so isothermality need not be assumed). We then consider the same problem in the context of the modified dynamics (MOND). After a brief comparison between scaling properties in the two theories, we study idealized MOND model filaments. A preliminary application to the segment of the Perseus-Pisces filament treated by ELT, gives MOND M/L estimates of order 10 s.u., compared with the Newtonian value of about 450, which ELT find. In spite of the large uncertainties still besetting the analysis, this instance of MOND application is of particular interest because: 1. Objects of this geometry have not been dealt with before. 2. It pertains to large-scale structure. 3. The typical accelerations involved are the lowest so far encountered in a semi-virialized system.Comment: 12 page

Gravitational Cherenkov losses in MOND theories

Survival of high-energy cosmic rays (HECRs) against gravitational Cherenkov losses is shown not to cast strong constraints on MOND theories that are compatible with general relativity (GR): theories that coincide with GR in the high-acceleration limit. The energy-loss rate, L, is shown to be many orders smaller than those derived in the literature for theories with no extra scale. The gravitational acceleration produced by a HECR in its vicinity is much higher than the MOND acceleration a0. So, modification to GR, which underlies L, enters only beyond the MOND radius of the particle, within which GR holds sway: r_M=sqrt(Gp/c a0). The spectral cutoff, which enters L quadratically, is thus 1/r_M, not the particle's, much larger, de Broglie wavenumber: k_{dB}= p/hbar. Thus, L is smaller than published rates, which use k_{dB}, by a factor (r_M k_{dB})^2~10^{39}(cp/3.10^{11}Gev)^3. With 1/r_M as cutoff, the distance a HECR can travel without major losses is q l_M, where l_M=c^2/a0 is the MOND length, and q is a dimensionless function of parameters of the problem. Since l_M is ~2 pi times the Hubble distance, survival of HECRs does not strongly constrain GR-compatible, MOND theories. Such theories also easily satisfy existing preferred-frame limits, inasmuch as these limits are gotten in high-acceleration systems. I exemplify the results with MOND adaptations of Einstein-Aether theories.Comment: Phys. Rev. Lett.; 4 pages; added some clarifications and reference

Modelling the Pioneer anomaly as modified inertia

This paper proposes an explanation for the Pioneer anomaly: an unexplained Sunward acceleration of 8.74 +/- 1.33 x 10^-10 m s^-2 seen in the behaviour of the Pioneer probes. Two hypotheses are made: (1) Inertia is a reaction to Unruh radiation and (2) this reaction is weaker for low accelerations because some wavelengths in the Unruh spectrum do not fit within a limiting scale (twice the Hubble distance) and are disallowed: a process similar to the Casimir effect. When these ideas are used to model the Pioneer crafts' trajectories there is a slight reduction in their inertial mass, causing an anomalous Sunward acceleration of 6.9 +/- 3.5 x 10^-10 m s^-2 which agrees within error bars with the observed Pioneer anomaly beyond 10 AU from the Sun. This new scheme is appealingly simple and does not require adjustable parameters. However, it also predicts an anomaly within 10 AU of the Sun, which has not been observed. Various observational tests for the idea are proposed.Comment: 15 pages, 2 bw figures, accepted by MNRAS 19th December 200

Galaxy groups and the modified dynamics

I estimate Modified-Dynamics (MOND), median M/L values for recently published catalogues of galaxy groups. While the median, Newtonian M/L values quoted for these catalogues are 110-200 solar units, the corresponding values for MOND are less than 10 solar units.Comment: 5 pages, Latex, to appear in Astrophys. J. Let

The Pioneer anomaly and the holographic scenario

In this paper we discuss the recently obtained relation between the Verlinde's holographic model and the first phenomenological Modified Newtonian dynamics. This gives also a promising possible explanation to the Pioneer anomaly.Comment: 5 pages, Accepted for publication in Astrophysics & Space Scienc

Cosmological fluctuation growth in bimetric MOND

I look at the growth of weak density inhomogeneities of nonrelativistic matter, in bimetric-MOND (BIMOND) cosmology. I concentrate on matter-twin-matter-symmetric versions of BIMOND, and assume that, on average, the universe is symmetrically populated in the two sectors. MOND effects are absent in an exactly symmetric universe, apart from the appearance of a cosmological constant, Lambda~(a0/c)^2. MOND effects-local and cosmological-do enter when density inhomogeneities that differ in the two sectors appear and develop. MOND later takes its standard form in systems that are islands dominated by pure matter. I derive the nonrelativistic equations governing small-scale fluctuation growth. The equations split into two uncoupled systems, one for the sum, the other for the difference, of the fluctuations in the two sectors. The former is governed strictly by Newtonian dynamics. The latter is governed by MOND dynamics, which entails stronger gravity, and nonlinearity even for the smallest of perturbations. These cause the difference to grow faster than the sum, conducing to matter-twin-matter segregation. The nonlinearity also causes interaction between nested perturbations on different scales. Because matter and twin matter (TM) repel each other in the MOND regime, matter inhomogeneities grow not only by their own self gravity, but also through shepherding by flanking TM overdensitie. The relative importance of gravity and pressure in the MOND system depends also on the strength of the perturbation. The development of structure in the universe, in either sector, thus depends crucially on two initial fluctuation spectra: that of matter alone and that of the matter-TM difference. I also discuss the back reaction on cosmology of BIMOND effects that appear as "phantom matter" resulting from inhomogeneity differences between the two sectors.Comment: 14 pages. Some clarifications added. Version published in Phys. Rev.

Distributive Justice and CEO Compensation

This paper develops a framework for studying individuals’ ideas about what constitutes just compensation for chief executive officers (CEOs) and reports estimates of just CEO pay and the principles guiding ideas of justice. The sample consists of students pursuing a Master of Business Administration (MBA) degree in Sweden and the United States. The framework, based on justice theory and making use of Rossi’s factorial survey method, enables assessment of ideas of fairness in CEO compensation, including (1) the just CEO compensation, in the eyes of each observer; (2) the principles of microjustice – observers’ ideas about “who should get what” based on characteristics of CEOs and their firms; and (3) principles of macrojustice – ideas about the just level and dispersion in compensation across all CEOs. Our estimates yield the following main results: First, there is broad agreement on the median just CEO compensation but substantial inter-individual variation in the principles of microjustice and the other principles of macrojustice. Second, there is remarkable similarity in the distributions of the principles of microjustice and macrojustice across the MBA groups. Other important results include a pervasive gender attentiveness among MBA students and tolerance for large variability in CEO pay.justice theory, fairness, CEO compensation, factorial survey method, MBA students, gender, inequality, Gini coefficient, Atikinson measure, Theil's inequality measures