Supersymmetric Localization in GLSMs for Supermanifolds

In this paper we apply supersymmetric localization to study gauged linear sigma models (GLSMs) describing supermanifold target spaces. We use the localization method to show that A-twisted GLSM correlation functions for certain supermanifolds are equivalent to A-twisted GLSM correlation functions for hypersurfaces in ordinary spaces under certain conditions. We also argue that physical two-sphere partition functions are the same for these two types of target spaces. Therefore, we reproduce the claim of arXiv:hep-th/9404186, arXiv:hep-th/9506070. Furthermore, we explore elliptic genera and (0,2) deformations and find similar phenomena.Comment: 31 pages, no figure

On the adaptive elastic-net with a diverging number of parameters

We consider the problem of model selection and estimation in situations where the number of parameters diverges with the sample size. When the dimension is high, an ideal method should have the oracle property [J. Amer. Statist. Assoc. 96 (2001) 1348--1360] and [Ann. Statist. 32 (2004) 928--961] which ensures the optimal large sample performance. Furthermore, the high-dimensionality often induces the collinearity problem, which should be properly handled by the ideal method. Many existing variable selection methods fail to achieve both goals simultaneously. In this paper, we propose the adaptive elastic-net that combines the strengths of the quadratic regularization and the adaptively weighted lasso shrinkage. Under weak regularity conditions, we establish the oracle property of the adaptive elastic-net. We show by simulations that the adaptive elastic-net deals with the collinearity problem better than the other oracle-like methods, thus enjoying much improved finite sample performance.Comment: Published in at http://dx.doi.org/10.1214/08-AOS625 the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

Did the Electronic Trading System Make the Foreign Exchange Market More Efficient?

This paper examines the effects of introducing the electronic trading system (EBS) on the foreign exchange market, the biggest financial market in the world where trading occurs through many dealers. We find that increasing transparency leads to an increase in informational efficiency, an important aspect of market quality. However, informed dealers are found to quote less aggressively in the more transparent market. Overall, we conclude that semi-transparency raises market efficiency in general, but that it is the uninformed dealers who benefit more from this increased efficiency

An X-ray diffraction Approach : Bulk mineral assemblages as provenance indicator of sediments from the Arctic Ocean

Paleoclimate research and climate models demonstrate that the Arctic is very sensitive to climate change and also plays a key role in driving and amplifying global climate variability and sea-level change. Study of the late Quaternary paleoceanography in the Arctic Ocean is of great importance to understand the glacial-interglacial climate changes. As the sediment in the central Arctic Ocean is mostly transported by iceberg and sea-ice, provenance studies can be used to infer the ice-sheet history and the surface circulation pattern. Bulk mineral assemblages are one of the proxies that can be used to identify the source areas of the Arctic sediments. The main aim of this thesis is to study in detail the quantitative X-Ray Diffraction (qXRD) software package RockJock which is used to obtain the bulk mineral assemblages result and the comparison of the two qXRD software packages RockJock and QUAX. In Chapter 4, three different sets of artificial mixtures are used to access the accuracy of RockJock, and the possible sources of errors are proposed. The comparison of RockJock and QUAX is based on the surface sediment samples retrieved from the Siberian shelf seas as well as the central Arctic Ocean. Quartz, feldspars, calcite, dolomite, and the sum of clay minerals show fairly good correlations, while the differences of individual clay minerals are high. In Chapter 5, surface sediment samples, which are used in Chapter 4, were analyzed using RockJock to test the possibility to use bulk mineral assemblages as provenance indicator. It shows that the combination of quartz, Qz/Fsp, dolomite and kaolinite can be used to identify source areas. Sediment input from the Canadian Arctic is generally characterized by high dolomite and Qz/Fsp values. Sediment input from the Eurasian Arctic shelf seas is generally characterized by low dolomite, Qz/Fsp, kaolinite values and high quartz values. Although the contents of amphibole are mostly too small to be quantified, the occurrence of amphibole might be an indicator of sediments from the Siberian shelf seas. In Chapter 6, three sediment cores selected from a transect across the Mendeleev Ridge were used in this thesis to study the provenance of terrigenous sediments from the Central Arctic in order to study the ice sheet history. It shows that the provenance of sediments deposited on the Makarov Basin side of the Mendeleev Ridge is different from that deposited on the Canada Basin side of the Mendeleev Ridge. The IRD events of MIS16, 12, 10, 8 are characterized by high dolomite contents, high quartz/feldspar ratios and low plagioclase contents and may suggest IRD input from the Canadian Archipelago. The IRD events that occur in MIS6, are characterized by high quartz and low dolomite contents, which indicates IRD from the Eurasian sources

Exact Cosmological Solutions of f(R)f(R) Theories via Hojman Symmetry

Nowadays, $f(R)$ theory has been one of the leading modified gravity theories to explain the current accelerated expansion of the universe, without invoking dark energy. It is of interest to find the exact cosmological solutions of $f(R)$ theories. Besides other methods, symmetry has been proved as a powerful tool to find exact solutions. On the other hand, symmetry might hint the deep physical structure of a theory, and hence considering symmetry is also well motivated. As is well known, Noether symmetry has been extensively used in physics. Recently, the so-called Hojman symmetry was also considered in the literature. Hojman symmetry directly deals with the equations of motion, rather than Lagrangian or Hamiltonian, unlike Noether symmetry. In this work, we consider Hojman symmetry in $f(R)$ theories in both the metric and Palatini formalisms, and find the corresponding exact cosmological solutions of $f(R)$ theories via Hojman symmetry. There exist some new solutions significantly different from the ones obtained by using Noether symmetry in $f(R)$ theories. To our knowledge, they also have not been found previously in the literature. This work confirms that Hojman symmetry can bring new features to cosmology and gravity theories.Comment: 16 pages, revtex4; v2: discussions added, Nucl. Phys. B in press; v3: published version. arXiv admin note: text overlap with arXiv:1505.0754

Model-Independent Constraints on Lorentz Invariance Violation via the Cosmographic Approach

Since Lorentz invariance plays an important role in modern physics, it is of interest to test the possible Lorentz invariance violation (LIV). The time-lag (the arrival time delay between light curves in different energy bands) of Gamma-ray bursts (GRBs) has been extensively used to this end. However, to our best knowledge, one or more particular cosmological models were assumed {\it a priori} in (almost) all of the relevant works in the literature. So, this makes the results on LIV in those works model-dependent and hence not so robust in fact. In the present work, we try to avoid this problem by using a model-independent approach. We calculate the time delay induced by LIV with the cosmic expansion history given in terms of cosmography, without assuming any particular cosmological model. Then, we constrain the possible LIV with the observational data, and find weak hints for LIV.Comment: 15 pages, 4 figures, 3 tables, revtex4; v2: discussions added, Phys. Lett. B in pres