23 research outputs found
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Nontopological Q-solitons and their Implications for Macroscopic Dark Matter
No full textQ-balls are stable, compact objects (more precisely, nontopological solitons) that can arise in complex scalar field theories with a U(1) symmetry in which the potential adheres to certain criteria. These objects are of phenomenological interest as candidates for macroscopic dark matter, an as of yet still relatively underconstrained region of dark matter parameter space. Many of the features of Q-balls -- including their size, charge, energy, and stability dynamics -- can be qualitatively and approximately quantitatively extracted from their potential under minimal assumptions, although exact solutions are only attainable numerically. A thorough analytic study of Q-balls leads to a simplified understanding of the interconnectedness of their parameters, attributes, and dynamics, culminating most notably in a direct mapping between global Q-ball parameters and related gauged and Proca Q-ball parameters.This work presents several novel results, as previously published by the author and collaborators, including: precise analytic profiles for global, gauged, and Proca Q-balls; proof of various Q-ball relations and identities; precise analytic estimates of a Q-ball's radius, charge, and energy in terms of a universal Q-ball parameter; new bounds on Q-ball radii and stability; and the aforementioned parameter mapping between global Q-balls and gauged and Proca Q-balls. More complex Q-solitons, including excited Q-balls and Q-shells, are also discussed. Together, these objects represent a new candidate class for dark matter
On the equivalence and non-equivalence of Dirac and Faddeev-Jackiw formalisms for constrained systems
No full textWe present a comparative analysis between the Dirac method and the original Faddeev-Jackiw formalism for constrained systems such as Dirac free field, Proca model, electromagnetism coupled to matter and source-free Maxwell field. We establish the possible differences between both approaches and show that they are not completely equivalent.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
Translating Feminism: Taiwan, Spivak, A-Wu
No full textEste artículo establece un diálogo entre las propuestas de Gayatri Spivak y las de la feminista taiwanesa A-Wu. Exponiendo las tensiones existentes dentro de los feminismos taiwaneses y su relación y negociación con las presiones imperialistas que configuran la identidad de la isla, la autora propone vías para una crítica recíproca entre grupos feministas que logre negociar productivamente con la universalización e intraducibilidad en cuyo marco tienen lugar los encuentros feministas transnacionales.This article establishes a dialogue between the proposals of Gayatri SPivak and Taiwanese scholar A-Wu. Through exposing the tensions, relationships, and negotiations between feminism in Taiwan and the imperialist pressures that shape the identity of the island, the author proposes ways for mutual criticism between feminists groups to negotiate productively with the universalization and the untranslatability that occur within transnational feminist gatherings
On infrared problems of effective Lagrangians of massive spin 2 fields coupled to gauge fields
No full textAbstractIn this paper we analyze the interactions of massive spin-2 particles charged under both Abelian and non-Abelian group using the Porrati–Rahman Lagrangian. This theory is valid up to an intrinsic cutoff scale. Phenomenologically a theory valid up to a cutoff scale is sensible as all known higher spin particles are non-fundamental and it is shown that indeed this action can be used to estimate some relevant cross section. Such action necessarily includes Stückelberg field and therefore it is necessary to fix the corresponding gauge symmetry. We show that this theory, when the Stückelberg symmetry is gauge-fixed, possesses a non-trivial infrared problem. A gauge fixing ambiguity arises which is akin to the Gribov problem in QCD in the Abelian case as well. In some cases (such as when the space–time is the four-dimensional torus) the vacuum copies can be found analytically. A similar phenomenon also appears in the case of Proca fields. A very interesting feature of these copies is that they arise only for “large enough” gauge potentials. This opens the possibility to avoid the appearance of such gauge fixing ambiguities by using a Gribov–Zwanziger like approach
Crystal symmetry and nonlinear optical properties
No full textIn an introductory section, the symmetry properties of some of the higher rank polar tensors relating to nonlinear optical polarization are briefly enumerated. It is noted that linear magneto-electric polarizability has been experimentally measured and that the reported results are in conformity with the theory. Symmetry properties of the higher rank axial tensors relating to nonlinear magneto-electric effect are enumerated and it is suggested that such an effect is possible in some crystals in the anti-ferromagnetic state. In all these studies, methods developed earlier by the author have been used
Some remarks on the optical rotatory dispersion of quartz
No full textThe quantum mechanical theory of rotary dispersion leads to the rule that the sum of the rotational strengths ∑ar of the various terms in a dispersion formula of the Drude type expressed in terms of the characteristic frequencies should be zero. It is shown in this paper that the rotary dispersion formulAbroken vertical bar for quartz which had been proposed earlier do not satisfy this summation rule. On the other hand, the single-term formula of the form ρ= Kλ2/(λ2−λ02)2 suggested by the present author which fits the data along the optic axis accurately from the visible to the ultra-violet region of the spectrum, fulfils the summation condition. It is also shown that the data of Bruhat and Grivet for the rotary dispersion of quartz normal to the optic axis is fitted well by a formula of the same form as that given above if we put K= −3.56 and λ0= 0.111355Aμ
The florachromes: their chemical nature and spectroscopic behaviour
No full textThis memoir presents detailed studies of the two florachromes discovered by the author and shown by him to be responsible for the colours exhibited by a great many flowers, the two florachromes being present in the petals either separately or together as the case may be. Their characteristic absorption spectra have been photographed and reproduced and also represented as spectrophotometric records of their aqueous solutions and of the acetone extracts of the floral pigments. In appropriate circumstances, the florachromes in solution are found to be quite stable and continue to exhibit their characteristic spectroscopic behaviours permanently. The interesting discovery is recorded that Florachrome B is present as the colouring matter of the fleshy leaves of the shrub Setcreasia purpurea and can be readily obtained therefrom. The relation between the structure of the florachromes and of the well-known organic compound flavone which is itself a colourless solid is discussed and an explanation is given why there are two florachromes with distinct spectroscopic behaviours
Magnet Shape Optimization to Reduce Pulsating Torque for a Five-Phase Permanent-Magnet Low-Speed Machine
No full textThe author would like to thank S. Djebarri from the Research Institute of Naval Academy for his help with computing the machines with FEA program FEMM and F. Byrne from the French Naval Academy for her English proofreadingFive-phase Surface-Mounted Permanent Magnet (SMPM) machines can inherently produce a smooth electromagnetic torque which can be increased when using third harmonic current injection. To really take advantage of these characteristics, the rotor magnets can be shaped in order to obtain a back-emf with large third harmonic term. This is the scope of the paper. For the design specifications of a low speed marine propulsion machine, the following objective must be achieved: to significantly mitigate the pulsating torque without reducing the average torque bearing in mind the solution where the rotor is made with full pole-pitch magnets. An analytical field computation, called equivalent coil method, is developed in order to quicly explore the magnet geometries. Thus a procedure to optimize small trapezoid notches at the surface of the pole magnets is performed. Referring to the classical fully pole-pitch magnet shape, the solution found allows a substantial reduction of the pulsating torque without reducing the torque density. Furthermore, with regard to an equivalent three-phase machine, for the same copper losses, the average torque of the optimized five-phase machine can be potentially higher if the third harmonic current injection is implemented
The second order Raman spectrum of diamond
No full textUsing an exceptional1y colourless plate of diamond of the ultra-violet transparent type and
the λ2536.5 resonance radiation of mercury as exciter, the author has photographed the second
order Raman spectrum of diamond with greatly increased intensity and much better resolved than any
recorded hitherto. The spectrum exhibits ten distinct Raman lines with frequency shifts 2176, 2190,
2225, 22531 2299, 2330, 2430, 2460, 2502 and 2666 cm-1. The frequency shifts of the first
five lines, in particular, correspond very closely with the positions of a set of five absorption
peaks observed by Robertson, Fox and Martin while exploring the absorption band in the region 4-4.8
μ with the aid of a concave grating of the echelette type. Of the ten observed second order
Raman lines, the more intense and prominent ones have been identified as octaves of the prominent
lattice frequencies of diamond appearing in the luminescence and absorption spectra. These facts are
irreconcilable with the consequences of the Born lattice dynamics. They can, however, be
satisfactorily explained on the basis of the Raman dynamics of crystal lattices. The relative
intensities of the second order Raman lines, as well as the ratios of the intensities of the Stokes,
the anti-Stokes and the octave of the principal Raman shift of 1332 cm-1 have been
estimated by photographic photometry
