3,087 research outputs found

### String-String triality for d=4, Z_2 orbifolds

We investigate the perturbative and non-perturbative correspondence of a
class of four dimensional dual string constructions with N=4 and N=2
supersymmetry, obtained as Z_2 or Z_2 x Z_2 orbifolds of the type II, heterotic
and type I string. In particular, we discuss the heterotic and type I dual of
all the symmetric Z_2 x Z_2 orbifolds of the type II string, classified in
hep-th/9901123. .Comment: latex, 50 pages, figures, final published versio

### Classification of the N=2, Z2 X Z2-symmetric type II orbifolds and their type II asymmetric duals

Using free world-sheet fermions, we construct and classify all the N=2, Z2 X
Z2 four-dimensional orbifolds of the type IIA/B strings for which the orbifold
projections act symmetrically on the left and right movers. We study the
deformations of these models out of the fermionic point, deriving the partition
functions at a generic point in the moduli of the internal torus T6=T2 X T2 X
T2. We investigate some of their perturbative and non-perturbative dualities
and construct new dual pairs of type IIA/type II asymmetric orbifolds, which
are related non-perturbatively and allow us to gain insight into some of the
non-perturbative properties of the type IIA/B strings in four dimensions. In
particular, we consider some of the (non-)perturbative gravitational
corrections.Comment: Latex, 47 pages, no figure

### The Thomson scattering cross section in a magnetized, high density plasma

We calculate the Thomson scattering cross section in a non-relativistic,
magnetized, high density plasma -- in a regime where collective excitations can
be described by magnetohydrodynamics. We show that, in addition to cyclotron
resonances and an elastic peak, the cross section exhibits two pairs of peaks
associated with slow and fast magnetosonic waves; by contrast, the cross
section arising in pure hydrodynamics possesses just a single pair of Brillouin
peaks. Both the position and the width of these magnetosonic-wave peaks depend
on the ambient magnetic field and temperature, as well as transport and
thermodynamic coefficients, and so can therefore serve as a diagnostic tool for
plasma properties that are otherwise challenging to measure.Comment: Main paper: pp 1-8. Appendix: pp 8-10. 2 figure

### Axion-like-particle decay in strong electromagnetic backgrounds

The decay of a massive pseudoscalar, scalar and U(1) boson into an
electron-positron pair in the presence of strong electromagnetic backgrounds is
calculated. Of particular interest is the constant-crossed-field limit,
relevant for experiments that aim to measure high-energy axion-like-particle
conversion into electron-positron pairs in a magnetic field. The total
probability depends on the quantum nonlinearity parameter - a product of field
and lightfront momentum invariants. Depending on the seed particle mass,
different decay regimes are identified. In the below-threshold case, we find
the probability depends on a non-perturbative tunnelling exponent depending on
the quantum parameter and the particle mass. In the above-threshold case, we
find that when the quantum parameter is varied linearly, the probability
oscillates nonlinearly around the spontaneous decay probability. A strong-field
limit is identified in which the threshold is found to disappear. In modelling
the fall-off of a quasi-constant-crossed magnetic field, we calculate
probabilities beyond the constant limit and investigate when the decay
probability can be regarded as locally constant.Comment: 22 pages, 7 figure

### Cauchyness and convergence in fuzzy metric spaces

[EN] In this paper we survey some concepts of convergence and Cauchyness appeared separately in the context of fuzzy metric spaces in the sense of George and Veeramani. For each convergence (Cauchyness) concept we find a compatible Cauchyness (convergence) concept. We also study the relationship among them and the relationship with compactness and completeness (defined in a natural sense for each one of the Cauchy concepts). In particular, we prove that compactness implies p-completeness.Almanzor Sapena acknowledges the support of Ministry of Economy and Competitiveness of Spain under grant TEC2013-45492-R.
ValentÃn Gregori acknowledges the support of Ministry of Economy and Competitiveness of Spain under grant MTM 2012-37894-C02-01.Gregori Gregori, V.; MiÃ±ana, J.; Morillas, S.; Sapena Piera, A. (2017). Cauchyness and convergence in fuzzy metric spaces. Revista de la Real Academia de Ciencias Exactas FÃsicas y Naturales Serie A MatemÃ¡ticas. 111(1):25-37. https://doi.org/10.1007/s13398-015-0272-0S25371111Alaca, C., Turkoglu, D., Yildiz, C.: Fixed points in intuitionistic fuzzy metric spaces. Chaos Solitons Fractals 29, 1073â€“1078 (2006)Edalat, A., Heckmann, R.: A computational model for metric spaces. Theor. Comput. Sci. 193, 53â€“73 (1998)Engelking, R.: General topology. PWN-Polish Sci. Publ, Warsawa (1977)Fang, J.X.: On fixed point theorems in fuzzy metric spaces. Fuzzy Sets Syst. 46(1), 107â€“113 (1992)George, A., Veeramani, P.: On some results in fuzzy metric spaces. Fuzzy Sets Syst. 64, 395â€“399 (1994)George, A., Veeramani, P.: Some theorems in fuzzy metric spaces. J. Fuzzy Math. 3, 933â€“940 (1995)George, A., Veeramani, P.: On some results of analysis for fuzzy metric spaces. Fuzzy Sets Syst. 90, 365â€“368 (1997)Grabiec, M.: Fixed points in fuzzy metric spaces. Fuzzy Sets Syst. 27, 385â€“389 (1989)Gregori, V., Romaguera, S.: Some properties of fuzzy metric spaces. Fuzzy Sets Syst. 115, 485â€“489 (2000)Gregori, V., Romaguera, S.: On completion of fuzzy metric spaces. Fuzzy Sets Syst. 130, 399â€“404 (2002)Gregori, V., Romaguera, S.: Characterizing completable fuzzy metric spaces. Fuzzy Sets Syst. 144, 411â€“420 (2004)Gregori, V., LÃ³pez-CrevillÃ©n, A., Morillas, S., Sapena, A.: On convergence in fuzzy metric spaces. Topol. Appl. 156, 3002â€“3006 (2009)Gregori, V., MiÃ±ana, J.J.: Some concepts realted to continuity in fuzzy metric spaces. In: Proceedings of the conference in applied topology WiATâ€™13, pp. 85â€“91 (2013)Gregori, V., MiÃ±ana, J.-J., Sapena, A.: On Banach contraction principles in fuzzy metric spaces (2015, submitted)Gregori, V., MiÃ±ana, J.-J.: std-Convergence in fuzzy metric spaces. Fuzzy Sets Syst. 267, 140â€“143 (2015)Gregori, V., MiÃ±ana, J.-J.: Strong convergence in fuzzy metric spaces Filomat (2015, accepted)Gregori, V., MiÃ±ana, J.-J., Morillas, S.: Some questions in fuzzy metric spaces. Fuzzy Sets Syst. 204, 71â€“85 (2012)Gregori, V., MiÃ±ana, J.-J., Morillas, S.: A note on convergence in fuzzy metric spaces. Iran. J. Fuzzy Syst. 11(4), 75â€“85 (2014)Gregori, V., Morillas, S., Sapena, A.: On a class of completable fuzzy metric spaces. Fuzzy Sets Syst. 161, 2193â€“2205 (2010)Gregori, V., Morillas, S., Sapena, A.: Examples of fuzzy metric spaces and applications. Fuzzy Sets Syst. 170, 95â€“111 (2011)Kramosil, I., Michalek, J.: Fuzzy metric and statistical metric spaces. Kybernetika 11, 326â€“334 (1975)Mihet, D.: On fuzzy contractive mappings in fuzzy metric spaces. Fuzzy Sets Syst. 158, 915â€“921 (2007)Mihet, D.: Fuzzy $\varphi$ Ï† -contractive mappings in non-Archimedean fuzzy metric spaces. Fuzzy Sets Syst. 159, 739â€“744 (2008)Mihet, D.: A Banach contraction theorem in fuzzy metric spaces. Fuzzy Sets Syst. 144, 431â€“439 (2004)Mishra, S.N., Sharma, N., Singh, S.L.: Common fixed points of maps on fuzzy metric spaces Internat. J. Math. Math. Sci. 17(2), 253â€“258 (1994)Morillas, S., Sapena, A.: On Cauchy sequences in fuzzy metric spaces. In: Proceedings of the conference in applied topology (WiATâ€™13), pp. 101â€“108 (2013)Ricarte, L.A., Romaguera, S.: A domain-theoretic approach to fuzzy metric spaces. Topol. Appl. 163, 149â€“159 (2014)Sherwood, H.: On the completion of probabilistic metric spaces. Z.Wahrschein-lichkeitstheorie verw. Geb. 6, 62â€“64 (1966)Sherwood, H.: Complete Probabilistic Metric Spaces. Z. Wahrschein-lichkeitstheorie verw. Geb. 20, 117â€“128 (1971)Tirado, P.: On compactness and G-completeness in fuzzy metric spaces. Iran. J. Fuzzy Syst. 9(4), 151â€“158 (2012)Tirado, P.: Contraction mappings in fuzzy quasi-metric spaces and [0,1]-fuzzy posets. Fixed Point Theory 13(1), 273â€“283 (2012)Vasuki, R., Veeramani, P.: Fixed point theorems and Cauchy sequences in fuzzy metric spaces. Fuzzy Sets Syst. 135(3), 415â€“417 (2003)Veeramani, P.: Best approximation in fuzzy metric spaces. J. Fuzzy Math. 9, 75â€“80 (2001

### R^2 Corrections and Non-perturbative Dualities of N=4 String ground states

We compute and analyse a variety of four-derivative gravitational terms in
the effective action of six- and four-dimensional type II string ground states
with N=4 supersymmetry. In six dimensions, we compute the relevant perturbative
corrections for the type II string compactified on K3. In four dimensions we do
analogous computations for several models with (4,0) and (2,2) supersymmetry.
Such ground states are related by heterotic-type II duality or type II-type II
U-duality. Perturbative computations in one member of a dual pair give a
non-perturbative result in the other member. In particular, the exact CP-even
R^2 coupling on the (2,2) side reproduces the tree-level term plus NS 5-brane
instanton contributions on the (4,0) side. On the other hand, the exact CP-odd
coupling yields the one-loop axionic interaction a.R\wedge R together with a
similar instanton sum. In a subset of models, the expected breaking of the
SL(2,Z)_S S-duality symmetry to a \Gamma(2)_S subgroup is observed on the
non-perturbative thresholds. Moreover, we present a duality chain that provides
evidence for the existence of heterotic N=4 models in which N=8 supersymmetry
appears at strong coupling.Comment: Latex2e, 51 pages, 1 figur

### Proton imaging of stochastic magnetic fields

Recent laser-plasma experiments report the existence of dynamically
significant magnetic fields, whose statistical characterisation is essential
for understanding the physical processes these experiments are attempting to
investigate. In this paper, we show how a proton imaging diagnostic can be used
to determine a range of relevant magnetic field statistics, including the
magnetic-energy spectrum. To achieve this goal, we explore the properties of an
analytic relation between a stochastic magnetic field and the image-flux
distribution created upon imaging that field. We conclude that features of the
beam's final image-flux distribution often display a universal character
determined by a single, field-scale dependent parameter - the contrast
parameter - which quantifies the relative size of the correlation length of the
stochastic field, proton displacements due to magnetic deflections, and the
image magnification. For stochastic magnetic fields, we establish the existence
of four contrast regimes - linear, nonlinear injective, caustic and diffusive -
under which proton-flux images relate to their parent fields in a qualitatively
distinct manner. As a consequence, it is demonstrated that in the linear or
nonlinear injective regimes, the path-integrated magnetic field experienced by
the beam can be extracted uniquely, as can the magnetic-energy spectrum under a
further statistical assumption of isotropy. This is no longer the case in the
caustic or diffusive regimes. We also discuss complications to the
contrast-regime characterisation arising for inhomogeneous, multi-scale
stochastic fields, as well as limitations currently placed by experimental
capabilities on extracting magnetic field statistics. The results presented in
this paper provide a comprehensive description of proton images of stochastic
magnetic fields, with applications for improved analysis of given proton-flux
images.Comment: Main paper pp. 1-29; appendices pp. 30-84. 24 figures, 2 table

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