Exotic Scalar States in the AdS/CFT Correspondence

We investigate a family of solutions of Type IIb supergravity which asymptotically approach AdS_5 X S^5 but contain a non-constant dilaton and volume scalar for the five-sphere. These solutions preserve an SO(1,3) X SO(6) symmetry. We discuss the solution in the context of the AdS/CFT correspondence, and we find that as well as running coupling from the nontrivial dilaton, the corresponding field theory has no supersymmetry and displays confinement at least for a certain range of parameters.Comment: 18 pages. 3 figures. Revised discussion section, added references. Final version to appear in JHE

Spin-Two Glueballs, Positive Energy Theorems and the AdS/CFT Correspondence

We determine the spectrum of graviton excitations in the background geometry of the AdS soliton in p+2 dimensions. Via the AdS/CFT correspondence this corresponds to determining the spectrum of spin two excitations in the dual effective p-dimensional field theories For the cases of D3- and M5-branes these are the spin two glueballs of QCD_3 and QCD_4 respectively. For all values of p we find an exact degeneracy of the spectra of these tensor states and certain scalar excitations. Our results also extend the perturbative proof of a positive energy conjecture for asymptotically locally AdS spacetimes (originally proposed for p=3) to an arbritrary number of dimensions.Comment: 25 pages, 3 figure

The Free Energy of N=4 Super-Yang-Mills and the AdS/CFT Correspondence

We compute the high-temperature limit of the free energy for four-dimensional N=4 supersymmetric SU(N_c) Yang-Mills theory. At weak coupling we do so for a general ultrastatic background spacetime, and in the presence of slowly-varying background gauge fields. Using Maldacena's conjectured duality, we calculate the strong-coupling large-N_c expression for the special case that the three-space has constant curvature. We compare the two results paying particular attention to curvature corrections to the leading order expressions.Comment: 26 pages.Minor corrections to eqs.(19),(21). Results and conclusions unchanged. References adde

Fractional Branes and the Entropy of 4D Black Holes

We reconsider the four dimensional extremal black hole constructed in type IIB string theory as the bound state of D1-branes, D5-branes, momentum, and Kaluza-Klein monopoles. Specifically, we examine the case of an arbitrary number of monopoles. Consequently, the weak coupling calculation of the microscopic entropy requires a study of the D1-D5 system on an ALE space. We find that the complete expression for the Bekenstein-Hawking entropy is obtained by taking into account the massless open strings stretched between the fractional D-branes which arise in the orbifold limit of the ALE space. The black hole sector therefore arises as a mixed Higgs-Coulomb branch of an effective 1+1 dimensional gauge theory.Comment: 12 pages. 1 figure. v2: References adde

Statistics of the geomagnetic secular variation for the past 5Ma

A new statistical model is proposed for the geomagnetic secular variation over the past 5Ma. Unlike previous models, the model makes use of statistical characteristics of the present day geomagnetic field. The spatial power spectrum of the non-dipole field is consistent with a white source near the core-mantle boundary with Gaussian distribution. After a suitable scaling, the spherical harmonic coefficients may be regarded as statistical samples from a single giant Gaussian process; this is the model of the non-dipole field. The model can be combined with an arbitrary statistical description of the dipole and probability density functions and cumulative distribution functions can be computed for declination and inclination that would be observed at any site on Earth's surface. Global paleomagnetic data spanning the past 5Ma are used to constrain the statistics of the dipole part of the field. A simple model is found to be consistent with the available data. An advantage of specifying the model in terms of the spherical harmonic coefficients is that it is a complete statistical description of the geomagnetic field, enabling us to test specific properties for a general description. Both intensity and directional data distributions may be tested to see if they satisfy the expected model distributions

Heat loss from colonies of bumblebees: mechanisms and consequences

Pollinating insects provide ecosystem services worth billions of dollars globally and the pollination of crop plants is vital for food security. Declines in pollinating insects have been associated with a variety of anthropogenic drivers of change. With a global population expected to reach nine billion by 2050 a better understanding of the relationship between agroecosystems and pollinators is required to maintain food security. Bumblebees are important pollinators that utilise efficient thermoregulation to develop their colonies. Heat loss by convection, conduction and radiation are potential obstacles to thermoregulation. Insulation limits heat loss and so behaviours of bumblebees that mitigate heat loss could have high adaptive significance. This thesis aimed to identify the relative importance of convection, conduction and radiation as mechanisms of heat loss from bumblebee colonies. Secondly, model the impacts of shortfalls in incubation on colony fecundity. Microcolonies of six orphaned worker bumblebees were used to the effect of different types of insulation of thermoregulation. Sugar consumption and average brood temperature were measured in order to determine the effects of different types of insulation, which allows insight into the mechanisms of heat loss in bumblebee nests. Developmental and demographic models were used to investigate the relationship between brood temperature on developmental time and colony fecundity in bumblebees. The results presented here show that heat loss by radiation is likely to be a small obstacle to thermoregulation in bumblebee nests. In contrast, insulation to reduce heat loss by convection and conduction resulted in higher average brood temperatures with no difference in syrup consumption compared to uninsulated boxes. Modelling revealed that queen production is highly sensitive to relatively small drops in average brood temperature. For example, a one degree reduction in average brood temperature from approximately 27.2⁰C to 26.2⁰C could result in an 11.4% reduction in queen production. The impact of nest thermoregulation on queen production highlights the adaptive significance of nesting behaviours, both the initial nest site choice by the queen and insulation behaviours of workers. The results of the model on the effect of temperature on colony fecundity demonstrate the mechanism by which shortfalls in incubation could reduce colony fecundity and result in declines in bumblebee populations

Geomagnetic spikes on the core-mantle boundary

Extreme variations of Earth’s magnetic field occurred in the Levant region around 1000 BC, when the field intensity rapidly rose and fell by a factor of 2. No coherent link currently exists between this intensity spike and the global field produced by the core geodynamo. Here we show that the Levantine spike must span >60° longitude at Earth’s surface if it originates from the core–mantle boundary (CMB). Several low intensity data are incompatible with this geometric bound, though age uncertainties suggest these data could have sampled the field before the spike emerged. Models that best satisfy energetic and geometric constraints produce CMB spikes 8–22° wide, peaking at O(100) mT. We suggest that the Levantine spike reflects an intense CMB flux patch that grew in place before migrating northwest, contributing to growth of the dipole field. Estimates of Ohmic heating suggest that diffusive processes likely govern the ultimate decay of geomagnetic spikes

Geomagnetic spikes on the core-mantle boundary

Extreme variations of Earth’s magnetic field occurred in the Levant region around 1000 BC, when the field intensity rapidly rose and fell by a factor of 2. No coherent link currently exists between this intensity spike and the global field produced by the core geodynamo. Here we show that the Levantine spike must span >60° longitude at Earth’s surface if it originates from the core–mantle boundary (CMB). Several low intensity data are incompatible with this geometric bound, though age uncertainties suggest these data could have sampled the field before the spike emerged. Models that best satisfy energetic and geometric constraints produce CMB spikes 8–22° wide, peaking at O(100) mT. We suggest that the Levantine spike reflects an intense CMB flux patch that grew in place before migrating northwest, contributing to growth of the dipole field. Estimates of Ohmic heating suggest that diffusive processes likely govern the ultimate decay of geomagnetic spikes

QCD4_4 Glueball Masses from AdS-6 Black Hole Description

By using the generalized version of gauge/gravity correspondence, we study the mass spectra of several typical QCD$_4$ glueballs in the framework of AdS$_6$ black hole metric of Einstein gravity theory. The obtained glueball mass spectra are numerically in agreement with those from the AdS$7 \times S^4$ black hole metric of the 11-dimensional supergravity.Comment: 10 pages, references updated and minor change