Vibrational assignments and line shapes in inelastic tunnelling spectroscopy: H on Cu(100)

We have carried out a computational study of the inelastic electron tunneling spectrum (IETS) of the two vibrational modes of a single hydrogen atom on a Cu(100) surface in a scanning tunneling microscopy (STM) junction. This study addresses key issues about vibrational assignment and line shape of observed peaks in IETS within the framework of density functional theory calculations and the Lorente-Persson theory for STM-IETS. We argue that the observation of only a single, broad peak in the STM-IETS [L.J. Lauhon and W. Ho, Phys. Rev. Lett. 85, 4566 (2000)] is not caused by any symmetry restrictions or any cancellation between inelastic and elastic vibrational contributions for one of the two modes but is due to strongly overlapping superposition of the contributions from the two modes caused by the rather large instrumental broadening and the narrow vibrational energy separation between the modes. In particular, we find that this broadening and the large asymmetry of the vibrational line shapes gives rise to substantial apparent vibrational energy shifts of the two modes and decrease their apparent energy separation

Loop corrections and a new test of inflation

Inflation is the leading paradigm for explaining the origin of primordial density perturbations and the observed temperature fluctuations of the cosmic microwave background. However many open questions remain, in particular whether one or more scalar fields were present during inflation and how they contributed to the primordial density perturbation. We propose a new observational test of whether multiple fields, or only one (not necessarily the inflaton) generated the perturbations. We show that our test, relating the bispectrum and trispectrum, is protected against loop corrections at all orders, unlike previous relations.Comment: 6 pages; v2: references added, minor changes; v3: Extended discussion, including the role of gravitational corrections. References added. Version accepted for publication in PR

Methods of payment and exporter's risk exposure: A view to exporter's payment risks and their management by different methods of payment during contracting for an international sale of goods

Crucially important to a seller of any merchandise is to know, whether or not he will in fact be paid for the goods he ships to his buyer. The question becomes even more important when a foreign element is added to the transaction in the form of a buyer located in a far-away country about which no one knows too much. The exporter faces a risk of not being able to obtain the money due to him even if he himself has fulfilled his part of the bargain. Facing that problem he may end up using all sorts of methods and mechanisms to lower his risk exposure to an acceptable level, still realising, that the possibility of something going wrong cannot be eliminated completely. Some of the methods of payment risk management, which the exporter can employ, fall outside the realms of that agreement of sale which he has with the buyer and some, on the other hand, he must include into the contract itself Different methods of effecting payment clearly belong to the latter group due to the fact that the parties always have to agree on some method of effecting payment, using which the buyer fulfils his part of the agreement. It is submitted that it would be impossible to discuss a broad topic such as this without leaving something important outside the scope of the paper. That has been done in the context of this paper by leaving out all procedural aspects that do not have an effect on the exporters security of payment. Especially in the section that discusses documentary credits, the workings of the credit and banking procedures have been cut to minimum in order to include aspects that in my mind were important. It follows that this paper is in, principle about the possibilities that an exporter has, to use methods of payment beneficially and economically during the period of drafting the contract of sale. Furthermore, it must be mentioned that by assuming that the exporter is a bona fide merchant I've decided to leave out the vast material and case law relating to the fraud exception in the context of documentary credits

Inflationary Infrared Divergences: Geometry of the Reheating Surface vs. delta N Formalism

We describe a simple way of incorporating fluctuations of the Hubble scale during the horizon exit of scalar perturbations into the delta N formalism. The dominant effect comes from the dependence of the Hubble scale on low-frequency modes of the inflaton. This modifies the coefficient of the log-enhanced term appearing in the curvature spectrum at second order in field fluctuations. With this modification, the relevant coefficient turns out to be proportional to the second derivative of the tree-level spectrum with respect to the inflaton phi at horizon exit. A logarithm with precisely the same coefficient appears in a calculation of the log-enhancement of the curvature spectrum based purely on the geometry of the reheating surface. We take this agreement as strong support for the proposed implementation of the delta N formalism. Moreover, our analysis makes it apparent that the log-enhancement of the inflationary power-spectrum is indeed physical if this quantity is defined using a global coordinate system on the reheating surface (or any other post-inflationary surface of constant energy density). However, it can be avoided by defining the spectrum using invariant distances on this surface.Comment: 13 pages, LaTeX. v3: Referencing improve

Correspondence between Loop-inspired and Braneworld Cosmology

Braneworld scenarios are motivated by string/M-theory and can be characterized by the way in which they modify the conventional Friedmann equations of Einstein gravity. An alternative approach to quantum gravity, however, is the loop quantum cosmology program. In the semi-classical limit, the cosmic dynamics in this scenario can also be described by a set of modified Friedmann equations. We demonstrate that a dynamical correspondence can be established between these two paradigms at the level of the effective field equations. This allows qualitatively similar features between the two approaches to be compared and contrasted as well as providing a framework for viewing braneworld scenarios in terms of constrained Hamiltonian systems. As concrete examples of this correspondence, we illustrate the relationships between different cosmological backgrounds representing scaling solutions

Non-chiral fusion rules, structure constants of D_m minimal models

We present a technique to construct, for $D_{m}$ unitary minimal models, the non-chiral fusion rules which determines the operator content of the operator product algebra. Using these rules we solve the bootstrap equations and therefore determine the structure constants of these models. Through this approach we emphasize the role played by some discrete symmetries in the classification of minimal models.Comment: 30 page