scholarly journals HELICAL MAGNETIC FIELDS FROM INFLATION

2009 ◽  
Vol 18 (09) ◽  
pp. 1395-1411 ◽  
Author(s):  
LEONARDO CAMPANELLI
Keyword(s):  
Magnetic Fields ◽  
Power Law ◽  
Background Field ◽  
Wave Number ◽  
Conformal Time ◽  
De Sitter ◽  
Simple Power ◽  
Dimensionless Constant ◽  
Real Positive Number

We analyze the generation of seed magnetic fields during de Sitter inflation considering a noninvariant conformal term in the electromagnetic Lagrangian of the form [Formula: see text], where I(ϕ) is a pseudoscalar function of a nontrivial background field ϕ. In particular, we consider a toy model that could be realized owing to the coupling between the photon and either a (tachyonic) massive pseudoscalar field or a massless pseudoscalar field nonminimally coupled to gravity, where I follows a simple power law behavior I(k,η) = g/(-kη)β during inflation, while it is negligibly small subsequently. Here, g is a positive dimensionless constant, k the wave number, η the conformal time, and β a real positive number. We find that only when β = 1 and 0.1 ≲ g ≲ 2 can astrophysically interesting fields be produced as excitation of the vacuum, and that they are maximally helical.

scholarly journals X-ray Properties of 3C 111: Separation of Primary Nuclear Emission and Jet Continuum

Universe ◽  
2020 ◽  
Vol 6 (11) ◽  
pp. 219
Author(s):  
Elena Fedorova ◽  
B.I. Hnatyk ◽  
V.I. Zhdanov ◽  
A. Del Popolo
Keyword(s):  
Accretion Disk ◽  
Power Law ◽  
Line Emission ◽  
High Energy ◽  
Power Law Model ◽  
X Ray ◽  
Additional Information ◽  
Observational Dataset ◽  
Simple Power ◽  
Photon Index

3C111 is BLRG with signatures of both FSRQ and Sy1 in X-ray spectrum. The significant X-ray observational dataset was collected for it by INTEGRAL, XMM-Newton, SWIFT, Suzaku and others. The overall X-ray spectrum of 3C 111 shows signs of a peculiarity with the large value of the high-energy cut-off typical rather for RQ AGN, probably due to the jet contamination. Separating the jet counterpart in the X-ray spectrum of 3C 111 from the primary nuclear counterpart can answer the question is this nucleus truly peculiar or this is a fake “peculiarity” due to a significant jet contribution. In view of this question, our aim is to estimate separately the accretion disk/corona and non-thermal jet emission in the 3C 111 X-ray spectra within different observational periods. To separate the disk/corona and jet contributions in total continuum, we use the idea that radio and X-ray spectra of jet emission can be described by a simple power-law model with the same photon index. This additional information allows us to derive rather accurate values of these contributions. In order to test these results, we also consider relations between the nuclear continuum and the line emission.

scholarly journals De Sitter and power-law solutions in non-local Gauss–Bonnet gravity

2018 ◽  
Vol 15 (11) ◽  
pp. 1850188 ◽  
Author(s):  
E. Elizalde ◽  
S. D. Odintsov ◽  
E. O. Pozdeeva ◽  
S. Yu. Vernov
Keyword(s):  
Power Law ◽  
Sufficient Conditions ◽  
Model Parameters ◽  
Local Form ◽  
De Sitter ◽  
Dynamical Equations ◽  
Non Local ◽  
Necessary And Sufficient ◽  
The Universe ◽  
Universe Evolution

The cosmological dynamics of a non-locally corrected gravity theory, involving a power of the inverse d’Alembertian, is investigated. Casting the dynamical equations into local form, the fixed points of the models are derived, as well as corresponding de Sitter and power-law solutions. Necessary and sufficient conditions on the model parameters for the existence of de Sitter solutions are obtained. The possible existence of power-law solutions is investigated, and it is proven that models with de Sitter solutions have no power-law solutions. A model is found, which allows to describe the matter-dominated phase of the Universe evolution.

Prediction of Bubbles, Crashes, and Antibubbles

2017 ◽  
Author(s):  
Didier Sornette
Keyword(s):  
Stock Market ◽  
Case Studies ◽  
Power Law ◽  
Statistical Tests ◽  
Statistical Significance ◽  
Large Market ◽  
Simple Power ◽  
Market Crashes ◽  
Successes And Failures

This chapter examines how to predict stock market crashes and other large market events as well as the limitations of forecasting, in particular in terms of the horizon of visibility and expected precision. Several case studies are presented in detail, with a careful count of successes and failures. After providing an overview of the nature of predictions, the chapter explains how to develop and interpret statistical tests of log-periodicity. It then considers the concept of an “antibubble,” using as an example the Japanese collapse from the beginning of 1990 to the present. It also describes the first guidelines for prediction, a hierarchy of prediction schemes that includes the simple power law, and the statistical significance of the forward predictions.

Statistics on Jupiter's Current Sheet with Juno Data: Geometry, Magnetic Fields and Energetic Particles

2021 ◽  
Author(s):  
Zhi-Yang Liu ◽  
Qiu-Gang Zong ◽  
Michel Blanc
Keyword(s):  
Magnetic Fields ◽  
Current Sheet ◽  
Power Law ◽  
Heavy Ions ◽  
Particle Interaction ◽  
The Other ◽  
Gaussian Functions ◽  
Fixed Energy ◽  
Thin Current Sheet ◽  
A Current

<p>Jupiter's magnetosphere contains a current sheet of huge size near its equator. The current sheet not only mediates the global mass and energy cycles of Jupiter's magnetosphere, but also provides an occurring place for many localized dynamic processes, such as reconnection and wave-particle interaction. To correctly evaluate its role in these processes, a statistical description of the current sheet is required. To this end, here we conduct statistics on Jupiter's current sheet, with four-year Juno data recorded in the 20-100 Jupiter radii, post-midnight magnetosphere. The results suggest a thin current sheet whose thickness is comparable with the gyro-radius of dominant ions. Magnetic fields in the current sheet decrease in power-law with increasing radial distances. At fixed energy, the flux of electrons and protons increases with decreasing radial distances. On the other hand, at fixed radial distances, the flux decreases in power-law with increasing energy. The flux also varies with the distances to the current sheet center. The corresponding relationship can be well described by Gaussian functions peaking at the current sheet center. In addition, the statistics show the flux of oxygen- and sulfur-group ions is comparable with the flux of protons at the same energy and radial distances, indicating the non-negligible effects of heavy ions on current sheet dynamics. From these results, a statistical model of Jupiter's current sheet is constructed, which provides us with a start point of understanding the dynamics of the whole Jupiter's magnetosphere.</p>

scholarly journals Small-Scale Solar Magnetic Fields

1976 ◽  
Vol 71 ◽  
pp. 69-99 ◽  
Author(s):  
J. O. Stenflo
Keyword(s):  
Magnetic Fields ◽  
Magnetic Flux ◽  
Solar Surface ◽  
Life Time ◽  
Wave Number ◽  
Small Scale ◽  
Solar Magnetic Fields ◽  
Field Amplification ◽  
Wave Numbers ◽  
Diffuse Form

The observed properties of small-scale solar magnetic fields are reviewed. Most of the magnetic flux in the photosphere is in the form of strong fields of about 100–200 mT (1–2 kG), which have remarkably similar properties regardless of whether they occur in active or quiet regions. These fields are associated with strong atmospheric heating. Flux concentrations decay at a rate of about 107 Wb s-1, independent of the amount of flux in the decaying structure. The decay occurs by smaller flux fragments breaking loose from the larger ones, i.e. a transfer of magnetic flux from smaller to larger Fourier wave numbers, into the wave-number regime where ohmic diffusion becomes significant. This takes place in a time-scale much shorter than the length of the solar cycle.The field amplification occurs mainly below the solar surface, since very little magnetic flux appears in diffuse form in the photosphere, and the life-time of the smallest flux elements is very short. The observations further suggest that most of the magnetic flux in quiet regions is supplied directly from below the solar surface rather than being the result of turbulent diffusion of active-region magnetic fields.

String inspired cosmological models through Lagrangian invariance

2020 ◽  
Vol 17 (06) ◽  
pp. 2050085
Author(s):  
José Antonio Belinchón ◽  
Danae Polychroni
Keyword(s):  
Perfect Fluid ◽  
Power Law ◽  
Matter Field ◽  
Scale Factor ◽  
Cosmological Models ◽  
De Sitter ◽  
Text Field ◽  
Duality Property ◽  
Constant Potential ◽  
Variable Potential

We study a string inspired cosmological with variable potential through the Lagrangian invariance method in order to determine the form of the potential. We have studied four cases by combining the different fields, that is, the dilaton [Formula: see text] the potential [Formula: see text] the [Formula: see text]-field and the matter field (a perfect fluid). In all the studied cases, we found that the potential can only take two possible forms: [Formula: see text] and [Formula: see text] where [Formula: see text] and [Formula: see text] are numerical constants. We conclude that when we take into account the Kalb–Ramond field, i.e. the [Formula: see text]-field, then it is only possible to get a constant potential, [Formula: see text] Nevertheless, if this field is not considered, then we get two possible solutions for the potential: [Formula: see text] and [Formula: see text] In all the cases, if the potential is constant, [Formula: see text] then we get a de Sitter like solution for the scale factor of the metric, [Formula: see text], which verifies the [Formula: see text]-duality property, while if the potential varies, then we get a power-law solution for the scale factor, [Formula: see text] [Formula: see text]

scholarly journals Energy conditions in non-local gravity

2019 ◽  
Vol 16 (10) ◽  
pp. 1950149 ◽  
Author(s):  
M. Ilyas
Keyword(s):  
Power Law ◽  
Arbitrary Function ◽  
Energy Conditions ◽  
De Sitter ◽  
Sitter Solution ◽  
Local Gravity ◽  
Non Local

We investigate the different energy conditions in non-local gravity, which is obtained by adding an arbitrary function of d’Alembertian operator, [Formula: see text], to the Hilbert–Einstein action. We analyze the validity of four different energy conditions and illustrate the different constraints over parameters of the power-law solution as well as de Sitter solution.

scholarly journals Near Infrared Polarimetry of Dark Clouds and Star Forming Regions - Two Micron Polarization Survey of T Tauri Stars

1990 ◽  
Vol 140 ◽  
pp. 327-328
Author(s):  
M. Tamura ◽  
S. Sato
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Near Infrared ◽  
Background Field ◽  
Star Forming ◽  
Dark Clouds ◽  
Star Forming Regions ◽  
Stellar Sources ◽  
Geometrical Relationship ◽  
The Magnetic Field

Infrared polarimetry is one of the most useful methods to delineate the magnetic field structure in dark clouds and star-forming regions, where the intracloud extinction is so large that optical polarimetry is inaccessible. We have been conducting a near-infrared polarization survey of background field stars and embedded sources toward nearby dark clouds and star-forming regions (Tamura 1988). Particularly, the magnetic field structure in the denser regions of the clouds are well revealed in Heiles Cloud 2 in Taurus, ρ Oph core, and NGC1333 region in Perseus (Tamura et al. 1987; Sato et al. 1988; Tamura et al. 1988). This survey also suggests an interesting geometrical relationship between magnetic field and star-formation: the IR polarization of young stellar sources associated with mass outflow phenomena is perpendicular to the magnetic fields. This relationship suggests a presence of circumstellar matter (probably dust disk) with its plane perpendicular to the ambient magnetic field. Combining with another geometrical relationship that the elongation of the denser regions of the cloud is perpendicular to the magnetic field, the geometry suggests that the cloud contraction and subsequent star-formation have been strongly affected by the magnetic fields. Thus, it is important to study the universality of such geometrical relationship between IR polarization of young stellar sources and magnetic fields. In this paper, we report the results on a 2 micron polarization survey of 39 T Tauri stars, 8 young stellar objects and 11 background field stars in Taurus dark cloud complex.

scholarly journals Decaying turbulence and magnetic fields in galaxy clusters

2019 ◽  
Vol 488 (3) ◽  
pp. 3439-3445 ◽  
Author(s):  
Sharanya Sur
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Galaxy Clusters ◽  
Power Law ◽  
Dynamo Action ◽  
Wide Range ◽  
Major Merger ◽  
Decaying Turbulence ◽  
Field Decay ◽  
The Magnetic Field

Abstract We explore the decay of turbulence and magnetic fields generated by fluctuation dynamo action in the context of galaxy clusters where such a decaying phase can occur in the aftermath of a major merger event. Using idealized numerical simulations that start from a kinetically dominated regime we focus on the decay of the steady state rms velocity and the magnetic field for a wide range of conditions that include varying the compressibility of the flow, the forcing wavenumber, and the magnetic Prandtl number. Irrespective of the compressibility of the flow, both the rms velocity and the rms magnetic field decay as a power law in time. In the subsonic case we find that the exponent of the power law is consistent with the −3/5 scaling reported in previous studies. However, in the transonic regime both the rms velocity and the magnetic field initially undergo rapid decay with an ≈t−1.1 scaling with time. This is followed by a phase of slow decay where the decay of the rms velocity exhibits an ≈−3/5 scaling in time, while the rms magnetic field scales as ≈−5/7. Furthermore, analysis of the Faraday rotation measure (RM) reveals that the Faraday RM also decays as a power law in time ≈t−5/7; steeper than the ∼t−2/5 scaling obtained in previous simulations of magnetic field decay in subsonic turbulence. Apart from galaxy clusters, our work can have potential implications in the study of magnetic fields in elliptical galaxies.

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