Large Distance Scales Research Articles

Inter-simple sequence repeat (ISSR) analysis of genetic variation of Chondrus crispus populations from North Atlantic

ISSR analysis was used to investigate genetic variations of 184 haploid and diploid samples from nine North Atlantic Chondrus crispus Stackhouse populations and one outgroup Yellow Sea Chondrus ocellatus Holmes population. Twenty-two of 50 primers were selected and 163 loci were scored for genetic diversity analysis. Genetic diversity varied among populations, percentage of polymorphic bands (PPB) ranged from 27.0 to 55.8%, H (Nei's genetic diversity) ranged from 0.11 to 0.20 and I (Shannon's information index) ranged from 0.16 to 0.30. Estimators PPB, H and I had similar values in intra-population genetic diversity, regardless of calculation methods. Analysis of molecular variance (AMOVA) apportioned inter-population and intra-population variations for C. crispus, showing more genetic variance (56.5%) occurred in intra-population, and 43.5% variation among nine populations. The Mantel test suggested that genetic differentiation between nine C. crispus populations was closely related with geographic distances ( R = 0.78, P = 0.002). Results suggest that, on larger distance scale (ca. >1000 km), ISSR analysis is useful for determining genetic differentiations of C. crispus populations including morphologically inseparable haploid and diploid individuals.

Is the Schwinger model at finite density a crystal?

It has been believed since the paper by Fischler, Kogut, and Susskind that in ${\mathrm{QED}}_{2}$ at finite charge density the chiral condensate exhibits a spatially inhomogeneous, oscillating behavior. In this paper we demonstrate that this inhomogeneity is due to the explicit breaking of the translational invariance by a uniform background charge density. Moreover, we investigate in the context of a simple statistical model what happens if the neutralizing background is composed instead of heavy, but dynamical, particles. We find that in contrast to the standard picture of Fischler et al., the chiral condensate will not exhibit coherent oscillations on large distance scales, unless the heavy neutralizing particles themselves form a crystal and the density is high.

DGP specteroscopy

We systematically explore the spectrum of gravitational perturbations in codimension-1 DGP braneworlds, and find a 4D ghost on the self-accelerating branch of solutions. The ghost appears for any value of the brane tension, although depending on the sign of the tension it is either the helicity-0 component of the lightest localized massive tensor of mass $0<m^2 < 2H^2$ for positive tension, the scalar `radion' for negative tension, or their admixture for vanishing tension. Because the ghost is gravitationally coupled to the brane-localized matter, the self-accelerating solutions are not a reliable benchmark for cosmic acceleration driven by gravity modified in the IR. In contrast, the normal branch of solutions is ghost-free, and so these solutions are perturbatively safe at large distance scales. We further find that when the $\mathbb{Z}_2$ orbifold symmetry is broken, new tachyonic instabilities, which are much milder than the ghosts, appear on the self-accelerating branch. Finally, using exact gravitational shock waves we analyze what happens if we relax boundary conditions at infinity. We find that non-normalizable bulk modes, if interpreted as 4D phenomena, may open the door to new ghost-like excitations.

General relativity in the undergraduate physics curriculum

Einstein’s general relativity is increasingly important in contemporary physics on the frontiers of very large distance scales (astrophysics and cosmology) and very small length scales (elementary particle physics). This paper makes the case for a “physics first” approach to introducing general relativity to undergraduate physics majors.

More about spontaneous Lorentz-violation and infrared modification of gravity

We consider a model with Lorentz-violating vector field condensates, in which dispersion laws of all perturbations, including tensor modes, undergo non-trivial modification in the infrared. The model is free of ghosts and tachyons at high 3-momenta. At low 3-momenta there are ghosts, and at even lower 3-momenta there exist tachyons. Still, with appropriate choice of parameters, the model is phenomenologically acceptable. Beyond a certain large distance scale and even larger time scale, the gravity of a static source changes from that of General Relativity to that of van Dam--Veltman--Zakharov limit of the Fierz--Pauli theory. Yet the late time cosmological evolution is always determined by the standard Friedmann equation, modulo small correction to the ``cosmological Planck mass'', so the modification of gravity cannot by itself explain the accelerated expansion of the Universe. We argue that the latter property is generic in a wide class of models with condensates.

Analysis of Ground-Measured and Passive-Microwave-Derived Snow Depth Variations in Midwinter across the Northern Great Plains

Abstract Accurate estimation of snow mass is important for the characterization of the hydrological cycle at different space and time scales. For effective water resources management, accurate estimation of snow storage is needed. Conventionally, snow depth is measured at a point, and in order to monitor snow depth in a temporally and spatially comprehensive manner, optimum interpolation of the points is undertaken. Yet the spatial representation of point measurements at a basin or on a larger distance scale is uncertain. Spaceborne scanning sensors, which cover a wide swath and can provide rapid repeat global coverage, are ideally suited to augment the global snow information. Satellite-borne passive microwave sensors have been used to derive snow depth (SD) with some success. The uncertainties in point SD and areal SD of natural snowpacks need to be understood if comparisons are to be made between a point SD measurement and satellite SD. In this paper three issues are addressed relating satellite derivation of SD and ground measurements of SD in the northern Great Plains of the United States from 1988 to 1997. First, it is shown that in comparing samples of ground-measured point SD data with satellite-derived 25 × 25 km2 pixels of SD from the Defense Meteorological Satellite Program Special Sensor Microwave Imager, there are significant differences in yearly SD values even though the accumulated datasets showed similarities. Second, from variogram analysis, the spatial variability of SD from each dataset was comparable. Third, for a sampling grid cell domain of 1° × 1° in the study terrain, 10 distributed snow depth measurements per cell are required to produce a sampling error of 5 cm or better. This study has important implications for validating SD derivations from satellite microwave observations.

CLASSICAL GHOSTS AND THE COSMOLOGICAL CONSTANT

For a large region of parameter space involving the cosmological constant and mass parameters, we discuss spacetime solutions that are effectively Minkowskian on large time and distance scales. A negative energy fluid is involved, resulting in a scale factor oscillating about a constant, with a frequency determined by the size of a negative cosmological constant. Gravity itself induces a coupling between the ghost-like and normal fields, and we find that this results in stochastic rather than unstable behavior. Ghosts could also allow for the existence of Lorentz invariant fluctuating solutions of finite energy density.

Fluctuations, ghosts, and the cosmological constant

For a large region of parameter space involving the cosmological constant and mass parameters, we discuss fluctuating spacetime solutions that are effectively Minkowskian on large time and distance scales. Rapid, small amplitude oscillations in the scale factor have a frequency determined by the size of a negative cosmological constant. A field with modes of negative energy is required. If it is gravity that induces a coupling between the ghost-like and normal fields, we find that this results in stochastic rather than unstable behavior. The negative energy modes may also permit the existence of Lorentz invariant fluctuating solutions of finite energy density. Finally we consider higher derivative gravity theories and find oscillating metric solutions in these theories without the addition of other fields.

Modified Gravity via Spontaneous Symmetry Breaking

We construct effective field theories in which gravity is modified via spontaneous breaking of local Lorentz invariance. This is a gravitational analogue of the Higgs mechanism. These theories possess additional graviton modes and modified dispersion relations. They are manifestly well-behaved in the UV and free of discontinuities of the van Dam-Veltman-Zakharov type, ensuring compatibility with standard tests of gravity. They may have important phenomenological effects on large distance scales, offering an alternative to dark energy. For the case in which the symmetry is broken by a vector field with the wrong sign mass term, we identify four massless graviton modes (all with positive-definite norm) and show the absence of the discontinuity.

Massive gravity on a brane

At present no theory of a massive graviton is known that is consistent with experiments at both long and short distances. The problem is that consistency with long distance experiments requires the graviton mass to be very small. Such a small graviton mass however implies an ultraviolet cutoff for the theory at length scales far larger than the millimeter scale at which gravity has already been measured. In this paper we attempt to construct a model which avoids this problem. We consider a brane world setup in warped AdS spacetime and we investigate the consequences of writing a mass term for the graviton on a the infrared brane where the local cutoff is of order a large (galactic) distance scale. The advantage of this setup is that the low cutoff for physics on the infrared brane does not significantly affect the predictivity of the theory for observers localized on the ultraviolet brane. For such observers the predictions of this theory agree with general relativity at distances smaller than the infrared scale but go over to those of a theory of massive gravity at longer distances. A careful analysis of the graviton two-point function, however, reveals the presence of a ghost in the low energy spectrum. A mode decomposition of the higher dimensional theory reveals that the ghost corresponds to the radion field. We also investigate the theory with a brane localized mass for the graviton on the ultraviolet brane, and show that the physics of this case is similar to that of a conventional four dimensional theory with a massive graviton, but with one important difference: when the infrared brane decouples and the would-be massive graviton gets heavier than the regular Kaluza--Klein modes, it becomes unstable and it has a finite width to decay off the brane into the continuum of Kaluza-Klein states.

Effective kinetic theory for high temperature gauge theories

Quasiparticle dynamics in relativistic plasmas associated with hot, weakly-coupled gauge theories (such as QCD at asymptotically high temperature T) can be described by an effective kinetic theory, valid on sufficiently large time and distance scales. The appropriate Boltzmann equations depend on effective scattering rates for various types of collisions that can occur in the plasma. The resulting effective kinetic theory may be used to evaluate observables which are dominantly sensitive to the dynamics of typical ultrarelativistic excitations. This includes transport coefficients (viscosities and diffusion constants) and energy loss rates. In this paper, we show how to formulate effective Boltzmann equations which will be adequate to compute such observables to leading order in the running coupling g(T) of high-temperature gauge theories [and all orders in 1/log g(T)−1]. As previously proposed in the literature, a leading-order treatment requires including both 2↔2 particle scattering processes as well as effective ``1↔2'' collinear splitting processes in the Boltzmann equations. The latter account for nearly collinear bremsstrahlung and pair production/annihilation processes which take place in the presence of fluctuations in the background gauge field. Our effective kinetic theory is applicable not only to near-equilibrium systems (relevant for the calculation of transport coefficients), but also to highly non-equilibrium situations, provided some simple conditions on distribution functions are satisfied.

Cosmic string induced sheetlike baryon inhomogeneities at the quark-hadron transition

Cosmic strings moving through matter produce wakes where the density is higher than the background density. We investigate the effects of such wakes occurring at the time of a first order quark-hadron transition in the early universe and show that they can lead to a separation of the quark-gluon plasma phase in the wake region, while the region outside the wake converts to the hadronic phase. Moving interfaces then trap large baryon densities in sheetlike regions which can extend across the entire horizon. A typical separation between such sheets, at formation, is of the order of 1 km. Regions of baryon inhomogeneity of this nature, i.e., having a planar geometry and separated by such large distance scales, appear to be well suited for recent models of inhomogeneous nucleosynthesis to reconcile the large baryon to photon ratio implied by the recent measurements of the cosmic microwave background power spectrum.

Development and testing of radionuclide transport models for fractured rock: examples from the Nagra/JNC Radionuclide Migration Programme in the Grimsel Test Site, Switzerland

The joint Swiss National Co-operative for the Disposal of Radioactive Waste (Nagra)/Japan Nuclear Cycle Development Institute (JNC) Radionuclide Migration Programme has now been on-going for over a decade in Nagra's Grimsel Test Site (GTS). The main aim of the programme has been the direct testing of radionuclide transport models in as realistic manner as possible. Although it will never be possible to fully test these models due to the large time and distance scales involved, tests of the model assumptions in scaled down but otherwise realistic conditions will contribute to developing confidence in the predictive power of the models. In this paper, the Nagra/JNC approach is highlighted with examples from a large programme of field, laboratory and natural analogue studies based around the GTS. The successes and failures are discussed as in the general approach to the thorough testing of predictive transport codes which will be used in repository performance assessment (PA). Some of the work is still on-going and this represents the first presentation of a unique set of results and conclusions.

Revealing Variety of Comets by Long-Term Monitoring Observation with a 50-cm Telescope

AbstractWe have been monitoring comets using the 50-cm telescope at the Mitaka campus of the National Astronomical Observatory, Japan since 1996. Over 20 comets, including bright ones such as comet C/1995 O1(Hale-Bopp), have been observed over long-term periods, namely over large heliocentric distance scales. Our samples show variety of comets in terms of both morphological and temporal variations. Several typical examples of various morphology, probably due to dust, are shown to emphasize the importance of long-term monitoring of comets.

An assessment of steady-state scale-up for small-scale geological models

The calculation of pseudo-relative permeabilities can be speeded up considerably by using steady-state methods. The capillary equilibrium limit may be assumed at small scales (30 cm or less), when the flood rate is low. At high flow rates and larger distance scales, we may use a viscous-dominated steady-state method which assumes constant fractional flow. Steady-state pseudos may also be calculated at intermediate flow rates using fine-scale simulations, and allowing the flood to come into equilibrium at different fractional flow levels. The aim of this paper is to assess the accuracy of steady-state scale-up for small-scale sedimentary structures. We have tested steady-state scale-up methods using a variety of small-scale geological models. The success of steady-state scale-up depends not only on the flow rate, but also on the nature of the heterogeneity. If high permeability zones are surrounded by low permeability ones (e.g. low permeability laminae or bed boundaries), oil trapping may occur in a water-wet system. In this case pseudo-oil-relative permeabilities are very sensitive to flow rate, and care must be taken to upscale using the correct viscous/capillary ratio. However, in permeability models, where phase trapping may not occur (unconnected low permeability regions), the pseudos are similar, whatever the viscous/capillary ratio. The disadvantage of steady-state scale-up is that it cannot take account of numerical dispersion, in the manner in which dynamic methods can. However, we show examples of coarse-scale simulations with viscous-dominated steady-state pseudos which agree favourably with fine-scale simulations. Provided there are sufficient grid blocks in the coarse-scale model, the smearing of the flood front due to numerical effects is not serious.

Effective theory forω≪k≪gTcolor dynamics in hot non-Abelian plasmas

A proper sequence of effective theories, corresponding to larger and larger distance scales, is crucial for analyzing real-time equilibrium physics in hot non-Abelian plasmas. For the study of color dynamics (by which I mean physics involving long wavelength gauge fluctuations), an important stepping stone in the sequence of effective theories is to have a good effective theory for dynamics with wave number k well below the Debye screening mass. I review how such dynamics is associated with inverse time scales $\ensuremath{\omega}\ensuremath{\ll}k.$ I then give a compact way to package, in the $\ensuremath{\omega}\ensuremath{\ll}k$ limit, B\"odeker's description of $k\ensuremath{\ll}m$ physics, which was in terms of Vlasov equations with collision terms. Finally, I show how the resulting effective theory can be reformulated as a path integral.

Exact Stationary States of a Two-Dimensional Transport Model

Previous calculations of transport coefficients of particle systems in two or more dimensions have used computer simulations or various approximations, like those implicit in the Boltzmann equation or in the standard probability theory of diffusion. Here an exactly solved model of crystal growth in three dimensions is transformed into a 2D model of steady particle transport. Then the exact, many-body stationary distribution and exact transport coefficients can be found as well as correlation functions. The model is highly asymmetric. In the transverse direction, particles are strongly attracted, so that long transverse rows of particles tend to form at low temperature. Kinks in these rows are rare, so the transverse positions of kinks effectively move continuously on a large distance scale.

Time dilation and the star formation scenario

We investigate the dependence of the redshift vs. brightness relation of GRBs upon the width of GRB luminosity function and the cosmological models. The relation is then fit to our observed time dilation data of GRBs. It is found that the best fit average luminosity ranges from in a standard candle luminosity model to in a cosmological model with a broad luminosity function . Our fits suggest that it is only possible to accomodate the large distance scale suggested by the Star Formation Rate model when the luminosity function has a large width in a cosmological model with low matter density .

IR limits, pregalactic stars, neutrino decay and quantum gravity

The results of recent studies which seek to probe fundamental aspects of astrophysics using TeV gamma-ray observations of active galactic nuclei (AGN) are presented. These analyses take advantage of both spectral and temporal information together with the unique combination of the very high energies and large distance scales involved. The next generation of instruments currently planned are expected to make substantial improvements in the study of such phenomena.

Blue spectra of Kalb-Ramond axions and fully anisotropic string cosmologies

The inhomogeneities associated with massless Kalb-Ramond axions can be amplified not only in isotropic (four-dimensional) string cosmological models but also in the fully anisotropic case. If the background geometry is isotropic, the axions (which are not part of the homogeneous background) develop outside the horizon, the growing modes leading, ultimately, to logarithmic energy spectra which are ``red'' in frequency and increase at large distance scales. We show that this conclusion can be avoided not only in the case of higher dimensional backgrounds with contracting internal dimensions but also in the case of string cosmological scenarios which are completely anisotropic in four dimensions. In this case the logarithmic energy spectra turn out to be ``blue'' in frequency and, consequently, decreasing at large distance scales. We elaborate on anisotropic dilaton-driven models and we argue that, incidentally, the background models leading to blue (or flat) logarithmic energy spectra for axionic fluctuations are likely to be isotropized by the effect of string tension corrections.