3,397 research outputs found
Top compositeness and precision unification
No full textThe evolution of standard model gauge couplings is studied in a nonsupersymmetric scenario in which the hierarchy problem is resolved by Higgs compositeness above the weak scale. It is argued that massiveness of the top quark combined with precision tests of the bottom quark imply that the right-handed top must also be composite. If, further, the standard model gauge symmetry is embedded into a simple subgroup of the unbroken composite-sector flavor symmetry, then precision coupling unification is shown to occur at â1015GeV, to a degree comparable to supersymmetric unification. © 2005 The American Physical Society
Strong Coupling and Weak Scale SUSY
No full textSundrum, Raman. (2010). Strong Coupling and Weak Scale SUSY. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/93291
Warped/composite phenomenology simplified
No full textThis is the first of two papers aimed at economically capturing the collider phenomenology of warped extra dimensions with bulk Standard Model fields, where the hierarchy problem is solved non-supersymmetrically. This scenario is related via the AdS/CFT correspondence to that of partial compositeness of the Standard Model. We present a purely four-dimensional, two-sector effective field theory describing the Standard Model fields and just their first Kaluza-Klein/composite excitations. This truncation, while losing some of the explanatory power and precision of the full higher-dimensional warped theory, greatly simplifies phenomenological considerations and computations. We describe the philosophy and explicit construction of our two-sector model, and also derive formulas for residual Higgs fine tuning and electroweak and flavor precision variables to help identify the most motivated parts of the parameter space. We highlight several of the most promising channels for LHC exploration. The present paper focusses on the most minimal scenario, while the companion paper addresses the even richer phenomenology of the minimal scenario of precision gauge couplin
Raman microspectroscopy interrogating 19th and 20th century painted trades union banners
No full textWe have previously developed protocols for the application of Raman microspectroscopy to studies on painted textiles. We have further assessed the value of such microanalyses in the identification of both inorganic and organic constituents, including original components and consolidants used in conservation treatments. This paper presents the results of a recent study on a number of 19th- and 20th-century trades union banners directed at collating a spectral database of inorganic pigments used in the illustrations and at probing the preparative process prior to painting. Such information will contribute to an understanding of the manufacture of such banners and their current condition, leading to the development of optimum conservation procedures.While Raman spectroscopy has the potential to be used in situ and, with the appropriate protocol, is non-destructive, nonetheless we have found that the analysis of resin-embedded cross-sections is to be preferred with microtoming providing the cleanest sample surface. The optimum methodology for acquiring good quality Raman spectra is described including operation in the confocal mode, with consideration of fluorescence, interference from resin, laser-induced photochemistry, and so on
Stimulated terahertz emission due to electronic Raman scattering in silicon
No full textSilicon-based semiconductors are intensively investigated over the past years as promising candidates for optoelectronic devices at terahertz (THz) frequencies [1]. Optically pumped intracenter silicon lasers, realized in the past decade in the THz range, are based on direct optical transitions between shallow levels of different shallow donors [2]. Recently, terahertz Raman laser emission has been demonstrated in silicon doped by antimony [3] and phosphorus [4].
We report on realization of terahertz lasers based on intracenter electronic Raman scattering in silicon doped by arsenic (Si:As, frequency range 4.8 – 5.1 THz and 5.9 – 6.5 THz) and silicon doped by bismuth (Si:Bi, 4.6 – 5.9 THz) under optical excitation by infrared frequency-tunable free electron laser at low lattice temperatures. The Stokes shift of the observed laser emission is equal to the Raman-active donor electronic transition between the ground 1s(A1) and the excited 1s(E) donor states. Raman terahertz gain of the lasers is similar to those observed for the donor-type terahertz silicon donor lasers
Infrared and Raman studies of thin polymer films
No full text[Keywords:- Waveguide; Raman; Attenuated Total Reflection; Infrared; Polymer Films; Barrier Films; Epoxy; Diffusion; Isocyanate; Crosslinking Agents; Cure Time; Kinetics; Urethane; Film Quality]This thesis describes the experimental work carried out between October l(^st), 1990 and 30th September, 1993, in the Chemistry Department of the University of Durham, in association with Courtaulds Coatings plc, m partial fulfilment of the requirements for the degree of Doctor of Philosophy. The thesis is divided into three sections, namely Theoretical Considerations (three Chapters), Experimental Results (three Chapters) and Discussion of Results (one Chapter). There are also three appendices. The theoretical section presents a working description of Paint Chemistry, Vibrational spectroscopy, Waveguide Raman Spectroscopy, Attenuated Total Reflection Fourier Transform Infrared Spectroscopy and Diffusion Processes. The experimental section is divided into three chapters. The first describes methods of film preparation and characterisation and includes methods of film thickness determination and the development of an off-line waveguiding rig at the University of Durham. Raman spectroscopic results are detailed in the second chapter, and include waveguide experiments on both single polymer films and laminate systems, some of which are reported for the first time, along with some FT-Raman results, also reported for the first time. The FT-IR ATR spectroscopic results are presented in the third chapter and include some barrier film studies on polymeric laminate systems, plus the study of certain diffusion processes, along with an estimation of the associated diffusion coefficients and some kinetic parameters, occurring in epoxy resins, which are reported for the first time. The discussion section concentrates on a full elucidation of the results, and conclusions that may be drawn from them, and ends with suggestions for future work. Refractive indices quoted, unless otherwise stated, refer to indices measured usmg 632.8 nm radiation, and have been estimated either using previous literature, or with the off-line rig. It is accepted that electric field calculations performed with these values will be slightly different to the actual fields observed in the Raman experiments, due to slightly different refractive indices at 514.5 nm. T in tables, unless otherwise stated, refers to band intensities in absorbance units. Finally, the attention of the reader is drawn to the fact that some of the materials used in the course of this project have no precise structure given. This is due to the fact that some of the substances used are of either a highly complicated and/or confidential nature
Towards objective endoscopic diagnosis of Barrett's associated early neoplasia using fibre-optic Raman Spectroscopy
No full textThis translational research evaluates a novel, custom-built Raman probe for potential
application as an in vivo diagnostic tool in the oesophagus. Raman spectroscopy (RS) is a
well established analytical technique which is capable of probing the biochemical changes
associated with neoplastic progression in oesophageal tissue. RS relies on measurement of
subtle inelastic scattering signals following monochromatic laser excitation.
Clinical utilisation of RS within hollow organs requires accurate collection and transmission
of signal through fibre-optic cables. This research aims to evaluate the ability of a custom
built fibre-optic Raman probe, in conjunction with multivariate classification models, to
differentiate between benign and neoplastic oesophageal pathologies ex vivo. The need for
spectral stability and reproducibility are addressed, as are difficulties associated with multisystem
reliability. In addition, the biochemical basis of spectral classification is evaluated and
discussed. Cont/d
The Interplay Between Natural and Accidental Supersymmetry
No full textIn this thesis, we will explore the subject of the little hierarchy problem which plagues solutions to the big hierarchy problem of the Standard Model of particle physics.
In the first half of this thesis, we study the theoretical framework for a supersymmetric resolution of the little hierarchy problem, known as natural supersymmetry, and argue that regions of the parameter space of this model have been missed by search strategies employed at the large hadron collider, but could be searched for with new search strategies.
In the second half of this thesis, we explore the possibility of embedding natural supersymmetry in models of warped extra dimensions in order to UV-complete them by utilizing a mechanism known as accidental supersymmetry. We study the mechanism of accidental supersymmetry in the Randall-Sundrum framework by focusing
on a toy model, and argue that accidental supersymmetry is capable solving the little hierarchy problem in that toy model. Finally, as models in the Randall-Sundrum framework themselves require UV completions, we demonstrate that it is possible to
realize the mechanism of accidental supersymmetry within the UV-complete framework of type IIB superstring theory
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