scholarly journals ULTRALIGHT SCALARS AND SPIRAL GALAXIES

2001 ◽  
Vol 16 (08) ◽  
pp. 513-530 ◽  
Author(s):  
GIA DVALI ◽  
GREGORY GABADADZE ◽  
M. SHIFMAN
Keyword(s):  
Scalar Field ◽  
Domain Wall ◽  
Wall Thickness ◽  
Domain Walls ◽  
Spiral Galaxies ◽  
Zero Mode ◽  
Scalar Particle ◽  
Additional Term ◽  
Massless Scalar ◽  
Logarithmic Term

We study some possible astrophysical implications of a very weakly coupled ultralight dilaton-type scalar field. Such a field may develop an (approximately stable) network of domain walls. The domain wall thickness is assumed to be comparable with the thickness of the luminous part of the spiral galaxies. The walls provide trapping for galactic matter. This is used to motivate the very existence of the spiral galaxies. A zero-mode existing on the domain wall is a massless scalar particle confined to (1+2) dimensions. At distances much larger than the galaxy/wall thickness, the zero-mode exchange generates a logarithmic potential, acting as an additional term with respect to Newton's gravity. The logarithmic term naturally leads to constant rotational velocities at the periphery. We estimate the scalar field coupling to the matter energy–momentum tensor needed to fit the observable flat rotational curves of the spiral galaxies. The value of this coupling turns out to be reasonable — we find no contradiction with the existing data.

scholarly journals Domain Walls from M-Branes

1997 ◽  
Vol 12 (15) ◽  
pp. 1087-1094 ◽  
Author(s):  
H. Lü ◽  
C. N. Pope
Keyword(s):  
Domain Wall ◽  
Dimensional Reduction ◽  
Domain Walls ◽  
Additional Term ◽  
Cosmological Term ◽  
Domain Wall Solution ◽  
Toroidal Compactifications ◽  
Four Manifolds ◽  
M Theory ◽  
Kaluza Klein

We discuss the vertical dimensional reduction of M-sbranes to domain walls in D=7 and D=4, by dimensional reduction on Ricci-flat four-manifolds and seven-manifolds. In order to interpret the vertically-reduced five-brane as a domain wall solution of a dimensionally-reduced theory in D=7, it is necessary to generalize the usual Kaluza–Klein ansatz, so that the three-form potential in D=11 has an additional term that can generate the necessary cosmological term in D=7. We show how this can be done for general four-manifolds, extending previous results for toroidal compactifications. By contrast, no generalization of the Kaluza–Klein ansatz is necessary for the compactification of M-theory to a D=4 theory that admits the domain-wall solution coming from the membrane in D=11.

scholarly journals Electromagnetic field with induced massive term: Case with scalar field

Open Physics ◽  
2011 ◽  
Vol 9 (5) ◽  
Author(s):  
Yuri Rybakov ◽  
Georgi Shikin ◽  
Yuri Popov ◽  
Bijan Saha
Keyword(s):  
Electromagnetic Field ◽  
Field Equation ◽  
Scalar Field ◽  
Cosmological Model ◽  
Bianchi Type ◽  
Rest Mass ◽  
Additional Term ◽  
Equation Of Motion ◽  
Massless Scalar ◽  
Type I

AbstractWe consider an interacting system of massless scalar and electromagnetic fields, with the Lagrangian explicitly depending on the electromagnetic potentials, i.e., interaction with broken gauge invariance. The Lagrangian for interaction is chosen in such a way that the electromagnetic field equation acquires an additional term, which in some cases is proportional to the vector potential of the electromagnetic field. This equation can be interpreted as the equation of motion of photon with induced nonzero rest-mass. This system of interacting fields is considered within the scope of Bianchi type-I (BI) cosmological model. It is shown that, as a result of interaction the isotropization process of the expansion takes place.

scholarly journals INFLUENCE OF THE MAGNETIC FIELD ON THE FERMION SCATTERING OFF BUBBLE AND KINK WALLS

2000 ◽  
Vol 15 (28) ◽  
pp. 1755-1766 ◽  
Author(s):  
P. CEA ◽  
G. L. FOGLI ◽  
L. TEDESCO
Keyword(s):  
Magnetic Field ◽  
Domain Wall ◽  
Domain Walls ◽  
Zero Mode ◽  
Bubble Wall ◽  
Electroweak Phase Transition ◽  
Transmission And Reflection Coefficients ◽  
The Magnetic Field ◽  
Transmission And Reflection

We investigate the scattering of fermions off domain walls at the electroweak phase transition in the presence of a magnetic field. We consider both the bubble wall and the kink domain wall. We derive and solve the Dirac equation for fermions with momentum perpendicular to the walls, and compute the transmission and reflection coefficients. In the case of kink domain wall, we briefly discuss the zero mode solutions localized on the wall. The possible role of the magnetic field for the electroweak baryogenesis is also discussed.

scholarly journals QUINTESSENCE AND BRANE WORLD SCENARIOS

2001 ◽  
Vol 16 (34) ◽  
pp. 2187-2195 ◽  
Author(s):  
Y. S. MYUNG
Keyword(s):  
Domain Wall ◽  
Domain Walls ◽  
Zero Mode ◽  
Negative Energy ◽  
Brane World ◽  
Negative Potential ◽  
Positive Pressure ◽  
Accelerating Universe ◽  
Negative Energy Density ◽  
Type Potential

We discuss the possibility of quintessence in the dilatonic domain walls including the Randall–Sundrum brane world. We obtain the zero mode effective action for gravitating objects in the dilatonic domain wall. First we consider the four-dimensional (4D) gravity and the Brans–Dicke graviscalar with a potential. This can be further rewritten as a minimally coupled scalar with the Liouville-type potential in the Einstein frame. However this model fails to induce the quintessence on the dilatonic domain wall because the potential is negative. Second we consider the 4D gravity with the dilaton. In this case we also find a negative potential. Any negative potential gives us negative energy density and positive pressure, which does not lead to an accelerating universe. Consequently it turns out that the zero mode approach of the dilatonic domain wall cannot accommodate the quintessence in cosmology.

scholarly journals Domain Walls in the Early Universe and Generation of Matter and Antimatter Domains

2018 ◽  
Vol 182 ◽  
pp. 02048
Author(s):  
A.D. Dolgov ◽  
S.I. Godunov ◽  
A.S. Rudenko
Keyword(s):  
Scalar Field ◽  
Domain Wall ◽  
Early Universe ◽  
Parameter Space ◽  
Related Problem ◽  
Domain Walls ◽  
Numerical Study ◽  
Parameter Region ◽  
Wall Width ◽  
Domain Wall Width

We present a model where it is possible to generate cosmologically large domains of matter and antimatter separated by cosmologically large distances. Domain walls existed only in the early universe and later they disappeared. So the problem of domain walls in this model does not exist. These features are achieved through a postulated form of interaction between inflaton and a new scalar field. This scenario inspired a study of the related problem - evolution of the domain wall width in expanding universe. According to classical results there is a region of parameter space where the solutions with constant physical width exist. Numerical study of the problem demonstrates that initial configurations tend to these solutions with time. However, we have found that the wall width can grow exponentially outside of that parameter region.

Cross-Sectional Observation of Nano-Domain Dots Formed in Congruent Single-Crystal LiTaO3

2006 ◽  
Vol 966 ◽  
Author(s):  
Yasuo Cho ◽  
Yasuhiro Daimon
Keyword(s):  
Domain Wall ◽  
Single Crystal ◽  
Wall Thickness ◽  
Domain Walls ◽  
Front Surface ◽  
Entire Sample ◽  
Cross Sectional ◽  
Depth Position ◽  
Measurement Results ◽  
Sectional Measurement

ABSTRACTCross-sectional shapes of reversal nano-domain dots formed in a congruent LiTaO3 single-crystal recording medium were studied by scanning nonlinear dielectric microscopy (SNDM). Images obtained by SNDM measurements confirm that reversal nano-domain dots penetrate through the entire sample. The domain wall thickness was evaluated by the cross-sectional measurement results. The variation of the domain wall thickness as a function of sample thickness and of depth position was evaluated. It was found that thinner samples have a tendency to have thinner domain walls, and it was confirmed that the domain wall thickness at the bottom of the sample was thinner than at the front surface of the sample. A discussion of the measured result is also provided.

scholarly journals GRAVITATIONAL HIGGS MECHANISM

2000 ◽  
Vol 15 (37) ◽  
pp. 2265-2280 ◽  
Author(s):  
ZURAB KAKUSHADZE ◽  
PETER LANGFELDER
Keyword(s):  
Scalar Field ◽  
Domain Wall ◽  
Plane Wave ◽  
Zero Mode ◽  
Transverse Dimension ◽  
Higgs Mechanism ◽  
The Other ◽  
Smooth Domain ◽  
Quantum Level ◽  
Other Hand

We discuss the gravitational Higgs mechanism in domain wall background solutions that arise in the theory of five-dimensional Einstein–Hilbert gravity coupled to a scalar field with a nontrivial potential. The scalar fluctuations in such backgrounds can be completely gauged away, and so can be the graviphoton fluctuations. On the other hand, we show that the graviscalar fluctuations do not have normalizable modes. As to the four-dimensional graviton fluctuations, in the case where the volume of the transverse dimension is finite the massive modes are plane-wave normalizable, while the zero mode is quadratically normalizable. We then discuss the coupling of domain wall gravity to localized four-dimensional matter. In particular, we point out that this coupling is consistent only if the matter is conformal. This is different from the Randall–Sundrum case as there is a discontinuity in the δ-function-like limit of such a smooth domain wall — the latter breaks diffeomorphisms only spontaneously, while the Randall–Sundrum brane breaks diffeomorphisms explicitly. Finally, at the quantum level both the domain wall as well as the Randall–Sundrum setups suffer from inconsistencies in the coupling between gravity and localized matter, as well as the fact that gravity is generically expected to be delocalized in such backgrounds due to higher curvature terms.

The direct determination of magnetic domain wall profiles using a split detector STEM

1978 ◽  
Vol 36 (1) ◽  
pp. 466-467
Author(s):  
J.N. Chapman ◽  
P.E. Batson ◽  
E.M. Waddell ◽  
R.P. Ferrier
Keyword(s):  
Electron Microscope ◽  
Domain Wall ◽  
Transmission Electron Microscope ◽  
Domain Walls ◽  
Photographic Plate ◽  
Magnetic Domain ◽  
Direct Determination ◽  
Quantitative Information ◽  
Scanning Transmission Electron Microscope ◽  
Transmission Electron

By far the most commonly used mode of Lorentz microscopy in the examination of ferromagnetic thin films is the Fresnel or defocus mode. Use of this mode in the conventional transmission electron microscope (CTEM) is straightforward and immediately reveals the existence of all domain walls present. However, if such quantitative information as the domain wall profile is required, the technique suffers from several disadvantages. These include the inability to directly observe fine image detail on the viewing screen because of the stringent illumination coherence requirements, the difficulty of accurately translating part of a photographic plate into quantitative electron intensity data, and, perhaps most severe, the difficulty of interpreting this data. One solution to the first-named problem is to use a CTEM equipped with a field emission gun (FEG) (Inoue, Harada and Yamamoto 1977) whilst a second is to use the equivalent mode of image formation in a scanning transmission electron microscope (STEM) (Chapman, Batson, Waddell, Ferrier and Craven 1977), a technique which largely overcomes the second-named problem as well.

The need of electron microscopy in the study of domains and domain walls in ferroelectrics

1994 ◽  
Vol 52 ◽  
pp. 550-551
Author(s):  
Wenwu Cao
Keyword(s):  
Domain Wall ◽  
Domain Walls ◽  
High Mobility ◽  
Continuum Theory ◽  
Polarization Vector ◽  
Ferroelectric Materials ◽  
Dielectric Constants ◽  
Nonlocal Coupling ◽  
Cubic Symmetry ◽  
Gradient Energy

Domain structures play a key role in determining the physical properties of ferroelectric materials. The formation of these ferroelectric domains and domain walls are determined by the intrinsic nonlinearity and the nonlocal coupling of the polarization. Analogous to soliton excitations, domain walls can have high mobility when the domain wall energy is high. The domain wall can be describes by a continuum theory owning to the long range nature of the dipole-dipole interactions in ferroelectrics. The simplest form for the Landau energy is the so called ϕ model which can be used to describe a second order phase transition from a cubic prototype,where Pi (i =1, 2, 3) are the components of polarization vector, α's are the linear and nonlinear dielectric constants. In order to take into account the nonlocal coupling, a gradient energy should be included, for cubic symmetry the gradient energy is given by,

Sign in / Sign up

Export Citation Format

Share Document