Racetrack Inflation

We develop a model of eternal topological inflation using a racetrack potential within the context of type IIB string theory with KKLT volume stabilization. The inflaton field is the imaginary part of the K\"ahler structure modulus, which is an axion-like field in the 4D effective field theory. This model does not require moving branes, and in this sense it is simpler than other models of string theory inflation. Contrary to single-exponential models, the structure of the potential in this example allows for the existence of saddle points between two degenerate local minima for which the slow-roll conditions can be satisfied in a particular range of parameter space. We conjecture that this type of inflation should be present in more general realizations of the modular landscape. We also consider `irrational' models having a dense set of minima, and discuss their possible relevance for the cosmological constant problem.Comment: 23 pages 7 figures. The final version with minor modifications, to appear in JHE

Generalized Second Law of Thermodynamics in f(T)f(T) Gravity with Entropy Corrections

We study the generalized second law (GSL) of thermodynamics in $f(T)$ cosmology. We consider the universe as a closed bounded system filled with $n$ component fluids in the thermal equilibrium with the cosmological boundary. We use two different cosmic horizons: the future event horizon and the apparent horizon. We show the conditions under which the GSL will be valid in specific scenarios of the quintessence and the phantom energy dominated eras. Further we associate two different entropies with the cosmological horizons: with a logarithmic correction term and a power-law correction term. We also find the conditions for the GSL to be satisfied or violated by imposing constraints on model parameters.Comment: 17 pages, no figure, title changed, version accepted for publication in Astrophysics and Space Scienc

Validation of TanDEM-X Surface Elevation on Devon Island Ice Cap

Remotely sensed surface elevation datasets are key to study mass balance and dynamic behaviours of glaciers, ice caps and ice sheets. Digital elevation models (DEM) generated from the TanDEM-X mission from single pass synthetic aperture radar interferometry (InSAR) at X-band provide an excellent potential resource for this purpose. However, they typically suffer from a negative bias in calculated surface elevations on glaciers due to penetration of radar waves in the snowpack and firn layers. Penetration depth depends on snowpack properties and acquisition parameters, and can be estimated using a simple model based on backscatter intensity, interferometric coherence and height of ambiguity parameters. To validate modelled penetration depths, multiple concurrent acquisitions of TanDEM-X images with ground measurements, airborne campaigns and spaceborne derived surface elevations were completed over Devon Island Ice Cap (75.25° N, 82.5° W) in the Canadian Arctic. Comparison of three TanDEM-X mosaic DEMs (winter 2010/11, 2013/14 and spring 2018) with differential GPS measurements (2011 and 2018), laser altimetry surveys (NASA ATM 2011 and SEARCH data 2018), and the Arctic DEM (2014), reveal an elevation bias of approximatively -3 m wherever firn layers are present below the snowpack. In this talk, we present corrected surface elevations for Devon Island Ice Cap and assess the spatial variability of penetration depths in relation to surface conditions and measured radar parameters. This validation case study improves the modelling of penetration depth for future application in all TanDEM-X DEMs over glaciated terrain

Mitochondrial Disease Sequence Data Resource (MSeqDR): a global grass-roots consortium to facilitate deposition, curation, annotation, and integrated analysis of genomic data for the mitochondrial disease clinical and research communities

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