The Minimum Total Mass of MACHOs and Halo Models of the Galaxy

If the density distribution \rho (r) of MACHOs is spherically symmetric with respect to the Galactic center, it is shown that the minimal total mass M_{min}^{{ MACHO}} of the MACHOs is 1.7\times 10^{10}\sol \tau_{-6.7}^{{ LMC}} where \tau_{-6.7}^{{ LMC}} is the optical depth (\tau^{{ LMC}}) toward the Large Magellanic Cloud (LMC) in the unit of 2\times 10^{-7}. If \rho (r) is a decreasing function of r, it is proved that M_{min}^{{ MACHO}} is 5.6\times 10^{10}\sol \tau_{-6.7}^{{ LMC}}. Several spherical and axially symmetric halo models of the Galaxy with a few free parameters are also considered. It is found that M_{min}^{{ MACHO}} ranges from 5.6\times 10^{10}\sol \tau_{-6.7}^{{ LMC}} to \sim 3 \times 10^{11}\sol \tau_{-6.7}^{{ LMC}}. For general case, the minimal column density \Sigma_{min}^{{ MACHO}} of MACHOs is obtained as \Sigma_{min}^{{ MACHO}} =25 \sol { pc}^{-2}\tau_{-6.7}^{{ LMC}}. If the clump of MACHOs exist only halfway between LMC and the sun, M_{min}^{{ MACHO}} is 1.5\times 10^9\sol. This shows that the total mass of MACHOs is smaller than 5 \times 10^{10}\sol , i.e. \sim 10\% of the mass of the halo inside LMC, either if the density distribution of MACHOs is unusual or \tau^{{ LMC}}\ll 2\times 10^{-7}.Comment: 5 pages, 5 Encapsulated PostScript figures, Latex, Accepted for publication in Apj. Letter

Shape of Deconstruction

We construct a six-dimensional Maxwell theory using a latticized extra space, the continuum limit of which is a shifted torus recently discussed by Dienes. This toy model exhibits the correspondence between continuum theory and discrete theory, and give a geometrical insight to theory-space model building.Comment: 10 pages, 2 figures, RevTeX4. a citation adde

Divergences in QED on a Graph

We consider a model of quantum electrodynamics (QED) on a graph. The one-loop divergences in the model are investigated by use of the background field method.Comment: 14 pages, no figures, RevTeX4. References and typos adde

Accessing Data: Methods for understanding mobile technology use

Mobile devices, applications and services have become integrated into people’s dailylives on a personal and professional level. Although traditional research methods arebeing used to understand the use of mobile devices and applications, methodologicalchallenges still exist. Researchers have responded to these challenges in a variety ofways, with an emphasis on developing methods that enable new ways of accessing,making available and collecting data about mobile technology use. This paper identifies,defines, describes and presents, a preliminary framework for understanding themethodological responses emerging in current Mobile Human Computer Interaction(Mobile HCI) research

Absence of evidence is not evidence of absence:On the limited use of regression discontinuity analysis in higher education

When higher education students are assessed multiple times, teachers need to consider how these assessments can be combined into a single pass or fail decision. A common question that arises is whether students should be allowed to take a resit. Previous research has found little to no clear learning benefits of resits and therefore suggested they might not be advantangeous as they are costly for both students and institutions. However, we conducted a simulation study that shows such a conclusion to be presumptuous. Absence of evidence is not evidence of absence; our results illustrate that if a resit effect were to exist, the analysis used in these studies (i.e. regression discontinuity analysis; RDA) lacked the power to detect such an effect. Power of RDA was only sufficient under extremely implausible conditions (i.e. large sample, large effect size, high correlation between examinations). To adequately compare the effect of assessment policies, researchers are recommended to use other methods than RDA

Discrete Gravitational Dimensions

We study the physics of a single discrete gravitational extra dimension using the effective field theory for massive gravitons. We first consider a minimal discretization with 4D gravitons on the sites and nearest neighbor hopping terms. At the linear level, 5D continuum physics is recovered correctly, but at the non-linear level the theory becomes highly non-local in the discrete dimension. There is a peculiar UV/IR connection, where the scale of strong interactions at high energies is related to the radius of the dimension. These new effects formally vanish in the limit of zero lattice spacing, but do not do so quickly enough to reproduce the continuum physics consistently in an effective field theory up to the 5D Planck scale. Nevertheless, this model does make sense as an effective theory up to energies parametrically higher than the compactification scale. In order to have a discrete theory that appears local in the continuum limit, the lattice action must have interactions between distant sites. We speculate on the relevance of these observations to the construction of finite discrete theories of gravity in four dimensions.Comment: 5 pages, 4 diagrams. Important typos in some equations corrected; conclusion s unchange

Bulk Fermion Stars with New Dimensions

Many efforts have been devoted to the studies of the phenomenology in particle physics with extra dimensions. We propose degenerate fermion stars with extra dimensions and study what features characterized by the size of extra dimensions should appear in its structure. We find that Kaluza-Klein excited modes arise for the larger scale of extra dimensions and examine the conditions on which different layers should be caused in the inside of the stars. We expound how the extra dimensions affect on physical quantities.Comment: 20 pages, 14 figure

Interparticle Potential up to Next-to-leading Order for Gravitational, Electrical, and Dilatonic Forces

Long-range forces up to next-to-leading order are computed in the framework of the Einstein-Maxwell-dilaton system by means of a semiclassical approach to gravity. As has been recently shown, this approach is effective if one of the masses under consideration is significantly greater than all the energies involved in the system. Further, we obtain the condition for the equilibrium of charged masses in the system.Comment: 19 pages, 19 figures, RevTeX4.1. Revised version, Title change

Coexistence of antiferromagnetic order and unconventional superconductivity in heavy fermion compounds CeRh_{1-x}Ir_xIn_5: nuclear quadrupole resonance studies

We present a systematic ^{115}In NQR study on the heavy fermion compounds CeRh_{1-x}Ir_xIn_5 (x=0.25, 0.35, 0.45, 0.5, 0.55 and 0.75). The results provide strong evidence for the microscopic coexistence of antiferromagnetic (AF) order and superconductivity (SC) in the range of 0.35 \leq x \leq 0.55. Specifically, for x=0.5, T_N is observed at 3 K with a subsequent onset of superconductivity at T_c=0.9 K. T_c reaches a maximum (0.94 K) at x=0.45 where T_N is found to be the highest (4.0 K). Detailed analysis of the measured spectra indicate that the same electrons participate in both SC and AF order. The nuclear spin-lattice relaxation rate 1/T_1 shows a broad peak at T_N and follows a T^3 variation below T_c, the latter property indicating unconventional SC as in CeIrIn_5 (T_c=0.4 K). We further find that, in the coexistence region, the T^3 dependence of 1/T_1 is replaced by a T-linear variation below T\sim 0.4 K, with the value \frac{(T_1)_{T_c}}{(T_1)_{low-T}} increasing with decreasing x, likely due to low-lying magnetic excitations associated with the coexisting magnetism.Comment: 20 pages, 14 figure