424,620 research outputs found
Ideal two-dimensional electron systems with a giant Rashba-type spin splitting in real materials: surfaces of bismuth tellurohalides
Spintronics is aimed at active controlling and manipulating the spin degrees
of freedom in semiconductor devices. A promising way to achieve this goal is to
make use of the tunable Rashba effect that relies on the spin-orbit interaction
(SOI) in a two-dimensional (2D) electron system immersed in an
inversion-asymmetric environment. The SOI induced spin-splitting of the
2D-electron state provides a basis for many theoretically proposed spintronic
devices. However, the lack of semiconductors with large Rashba effect hinders
realization of these devices in actual practice. Here we report on a giant
Rashba-type spin splitting in 2D electron systems which reside at
tellurium-terminated surfaces of bismuth tellurohalides. Among these
semiconductors, BiTeCl stands out for its isotropic metallic surface-state band
with the Gamma-point energy lying deep inside the bulk band gap. The giant
spin-splitting of this band ensures a substantial spin asymmetry of the
inelastic mean free path of quasiparticles with different spin orientations.Comment: 12 pages, 5 figure
Scalar field in cosmology: Potential for isotropization and inflation
The important role of scalar field in cosmology was noticed by a number of
authors. Due to the fact that the scalar field possesses zero spin, it was
basically considered in isotropic cosmological models. If considered in an
anisotropic model, the linear scalar field does not lead to isotropization of
expansion process. One needs to introduce scalar field with nonlinear potential
for the isotropization process to take place. In this paper the general form of
scalar field potentials leading to the asymptotic isotropization in case of
Bianchi type-I cosmological model, and inflationary regime in case of isotropic
space-time is obtained. In doing so we solved both direct and inverse problem,
where by direct problem we mean to find metric functions and scalar field for
the given potential, whereas, the inverse problem means to find the potential
and scalar field for the given metric function. The scalar field potentials
leading to the inflation and isotropization were found both for harmonic and
proper synchronic time.Comment: 10 page
Black-brane solution for C_2 algebra
Black p-brane solutions for a wide class of intersection rules and Ricci-flat
``internal'' spaces are considered. They are defined up to moduli functions H_s
obeying non-linear differential equations with certain boundary conditions
imposed. A new solution with intersections corresponding to the Lie algebra C_2
is obtained. The functions H_1 and H_2 for this solution are polynomials of
degree 3 and 4.Comment: 12 pages, Latex, submitted to J. Math. Phy
On the "scattering law" for Kasner parameters in the model with one-component anisotropic fluid
A multidimensional cosmological type model with 1-component anisotropic fluid
is considered. An exact solution is obtained. This solution is defined on a
product manifold containing n Ricci-flat factor spaces. We singled out a
special solution governed by the function cosh. It is shown that this special
solution has Kasner-like asymptotics in the limits \tau \to + 0 and
\tau \to + \infty, where \tau is a synchronous time variable. A relation
between two sets of Kasner parameters \alpha_{\infty} and \alpha_{0} is found.
This formula (of "scattering law") is coinciding with that obtained earlier for
the S-brane solution (when scalar fields are absent).Comment: 23 pages, 1 figure, Late
Finite-time Singularities in Swampland-related Dark Energy Models
In this work we shall investigate the singularity structure of the phase
space corresponding to an exponential quintessence dark energy model recently
related to swampland models. The dynamical system corresponding to the
cosmological system is an autonomous polynomial dynamical system, and by using
a mathematical theorem we shall investigate whether finite-time singularities
can occur in the dynamical system variables. As we demonstrate, the solutions
of the dynamical system are non-singular for all cosmic times and this result
is general, meaning that the initial conditions corresponding to the regular
solutions, belong to a general set of initial conditions and not to a limited
set of initial conditions. As we explain, a dynamical system singularity is not
directly related to a physical finite-time singularity. Then, by assuming that
the Hubble rate with functional form , is a
solution of the dynamical system, we investigate the implications of the
absence of finite-time singularities in the dynamical system variables. As we
demonstrate, Big Rip and a Type IV singularities can always occur if
respectively. However, Type II and Type III
singularities cannot occur in the cosmological system, if the Hubble rate we
quoted is considered a solution of the cosmological system.Comment: EPL Accepte
Cosmological dynamics in six-order gravity
We consider cosmological dynamics in generalized modified gravity theory with
the term added to the action of the form . Influence of term to the known solutions of modified gravity is described. We show
that in particular case of these two non-Einstein terms are equally
important on power-law solutions. These solutions and their stability have been
studied using dynamical system approach. Some results for the case of
(including stability of de Sitter solution in the theory under investigation)
have been found using other methods
On a general class of brane-world black holes
We use the general solution to the trace of the 4-dimensional Einstein
equations for static, spherically symmetric configurations as a basis for
finding a general class of black hole (BH) metrics, containing one arbitrary
function which vanishes at some , the horizon
radius. Under certain reasonable restrictions, BH metrics are found with or
without matter and, depending on the boundary conditions, can be asymptotically
flat or have any other prescribed large behaviour. It is shown that this
procedure generically leads to families of solutions unifying non-extremal
globally regular BHs with a Kerr-like global structure, extremal BHs and
symmetric wormholes. Horizons in space-times with zero scalar curvature are
shown to be either simple or double. The same is generically true for horizons
inside a matter distribution, but in special cases there can be horizons of any
order. A few simple examples are discussed. A natural application of the above
results is the brane world concept, in which the trace of the 4D gravity
equations is the only unambiguous equation for the 4D metric, and its solutions
can be continued into the 5D bulk according to the embedding theorems.Comment: 9 pages, revtex
Toda p-brane black holes and polynomials related to Lie algebras
Black hole generalized p-brane solutions for a wide class of intersection
rules are obtained. The solutions are defined on a manifold that contains a
product of n - 1 Ricci-flat internal spaces. They are defined up to a set of
functions H_s obeying non-linear differential equations equivalent to Toda-type
equations with certain boundary conditions imposed. A conjecture on polynomial
structure of governing functions H_s for intersections related to semisimple
Lie algebras is suggested. This conjecture is proved for Lie algebras: A_m,
C_{m+1}, m > 0. For simple Lie algebras the powers of polynomials coincide with
the components of twice the dual Weyl vector in the basis of simple coroots.
The coefficients of polynomials depend upon the extremality parameter \mu >0.
In the extremal case \mu = 0 such polynomials were considered previously by H.
L\"u, J. Maharana, S. Mukherji and C.N. Pope. Explicit formulas for
A_2-solution are obtained. Two examples of A_2-dyon solutions, i.e. dyon in D =
11 supergravity with M2 and M5 branes intersecting at a point and Kaluza-Klein
dyon, are considered.Comment: 24 pages, Latex, typos are eliminated, a correct relation on
parameters of special block-orthogonal solution is added in third line after
eq. (4.10
Diversity of universes created by pure gravity
We show that a number of problems of modern cosmology may be solved in the
framework of multidimensional gravity with high-order curvature invariants,
without invoking other fields. We use a method employing a slow-change
approximation, able to work with rather a general form of the gravitational
action, and consider Kaluza-Klein type space-times with one or several extra
factor spaces. A vast choice of effective theories suggested by the present
framework may be stressed: even if the initial Lagrangian is entirely fixed,
one obtains quite different models for different numbers, dimensions and
topologies of the extra factor spaces. As examples of problems addressed we
consider (i) explanation of the present accelerated expansion of the Universe,
with a reasonably small cosmological constant, and the problem of its fine
tuning is considered from a new point of view; (ii) the mechanism of closed
wall production in the early Universe; such walls are necessary for massive
primordial black hole formation which is an important stage in some scenarios
of cosmic structure formation; (iii) sufficient particle production rate at the
end of inflation; (iv) it is shown that our Universe may contain spatial
domains with a macroscopic size of extra dimensions. We also discuss chaotic
attractors appearing at possible nodes of the kinetic term of the effective
scalar field Lagrangian.Comment: 14 pages, 8 figures, revtex4. Final version, some considerations
added in response to referee remark
Uniformization and an Index Theorem for Elliptic Operators Associated with Diffeomorphisms of a Manifold
We consider the index problem for a wide class of nonlocal elliptic operators
on a smooth closed manifold, namely differential operators with shifts induced
by the action of an isometric diffeomorphism. The key to the solution is the
method of uniformization: We assign to the nonlocal problem a
pseudodifferential operator with the same index, acting in sections of an
infinite-dimensional vector bundle on a compact manifold. We then determine the
index in terms of topological invariants of the symbol, using the Atiyah-Singer
index theorem.Comment: 16 pages, no figure
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