392 research outputs found
Band Structure of the Growth Rate of the Two-Stream Instability of an Electron Beam Propagating in a Bounded Plasma
This paper presents a study of the two-stream instability of an electron beam
propagating in a finite-size plasma placed between two electrodes. It is shown
that the growth rate in such a system is much smaller than that of an infinite
plasma or a finite size plasma with periodic boundary conditions. Even if the
width of the plasma matches the resonance condition for a standing wave, a
spatially growing wave is excited instead with the growth rate small compared
to that of the standing wave in a periodic system. The approximate expression
for this growth rate is , where is the
electron plasma frequency, and are the beam and the plasma
densities, respectively, is the beam velocity, and is the plasma
width. The frequency, wave number and the spatial and temporal growth rates as
functions of the plasma size exhibit band structure. The amplitude of
saturation of the instability depends on the system length, not on the beam
current. For short systems, the amplitude may exceed values predicted for
infinite plasmas by more than an order of magnitude.Comment: 9 page
New Cosmic Low Energy States of Neutrino
A field theory is studied where the consistency condition of equations of
motion dictates strong correlation between states of "primordial" fermion
fields and local value of the dark energy. In regime of the fermion densities
typical for normal particle physics, the primordial fermions split into three
families identified with regular fermions. When fermion energy density is
comparable with dark energy density, the theory allows transition to new type
of states. The possibility of such Cosmo-Low Energy Physics (CLEP) states is
demonstrated in a model of FRW universe filled with homogeneous scalar field
and uniformly distributed nonrelativistic neutrinos. Neutrinos in CLEP state
are drawn into cosmological expansion by means of dynamically changing their
own parameters. One of the features of the fermions in CLEP state is that in
the late time universe their masses increase as ( is the
scale factor). The energy density of the cold dark matter consisting of
neutrinos in CLEP state scales as a sort of dark energy; this cold dark matter
possesses negative pressure and for the late time universe its equation of
state approaches that of the cosmological constant. The total energy density of
such universe is less than it would be in the universe free of fermionic matter
at all.Comment: Contributed to XXXIX Rencontres de Moriond "Exploring the Universe.
Contents and Structure of the Universe", La Thuile, Aosta, Italy, March 28 -
April 4, 200
k-Essence, Avoidance of the Weinberg's Cosmological Constant No-Go Theorem and Other Dark Energy Effects of Two Measures Field Theory
The dilaton-gravity sector of the Two Measures Field Theory (TMT) is explored
in detail in the context of cosmology. The dilaton \phi dependence of the
effective Lagrangian appears only as a result of the spontaneous breakdown of
the scale invariance. If no fine tuning is made, the effective \phi-Lagrangian
p(\phi,X) depends quadratically upon the kinetic energy X. Hence TMT may
represent an explicit example of the effective k-essence resulting from first
principles without any exotic term in the fundamental action intended for
obtaining this result. Depending of the choice of regions in the parameter
space, TMT exhibits different possible outputs for cosmological dynamics: a)
Possibility of resolution of the old cosmological constant (CC) problem. From
the point of view of TMT, it becomes clear why the old CC problem cannot be
solved (without fine tuning) in the conventional field theories (i.e theories
with only the measure of integration \sqrt{-g} in the action). b) The power law
inflation without any fine tuning can end with damped oscillations of \phi
around the state with zero CC. d) There is a broad range of the parameters such
that: in the late time universe w=p/\rho <-1 and asymptotically (as t\to\infty)
approaches -1 from below; \rho approaches a cosmological constant. The
smallness of the CC may be achieved without fine tuning of dimensionfull
parameters: either by a seesaw type mechanism or due to a correspondence
principle between TMT and conventional field theories.Comment: 25 pages, 11 figures; more detailed and improved explanation
presented on how the Weinberg's no-go theorem is avoided; references adde
Gauge Unified Theories without the Cosmological Constant Problem
We study gauge theories in the context of a gravitational theory without the
cosmological constant problem (CCP). The theory is based on the requirement
that the measure of integration in the action is not necessarily
but it is determined dynamically through additional degrees of freedom.
Realization of these ideas in the framework of the first order formalism solves
the CCP. Incorporation of a condensate of a four index field strength allows,
after a conformal transformation to the Einstein frame, to represent the system
of gravity and matter in the standard GR form. Now, however, the effective
potential vanishes at a vacuum state due to the exact balance to zero of the
gauge fields condensate and the original scalar fields potential. As a result
it is possible to combine the solution of the CCP with: a) inflation and
transition to a phase without fine tuning after a reheating
period; b) spontaneously broken gauge unified theories (including fermions).
The model opens new possibilities for a solution of the hierarchy problem.Comment: LaTeX, 25 page
Higgs-Inflaton Symbiosis, Cosmological Constant Problem and Superacceleration Phase of the Universe in Two Measures Field Theory with Spontaneously Broken Scale Invariance
We study the scalar sector of the Two Measures Field Theory (TMT) model in
the context of cosmological dynamics. The scalar sector includes the inflaton
\phi and the Higgs \upsilon fields. The model possesses gauge and scale
invariance. The latter is spontaneously broken due to intrinsic features of the
TMT dynamics. In the model with the inflaton \phi alone, in different regions
of the parameter space the following different effects can take place without
fine tuning of the parameters and initial conditions: a) Possibility of
resolution of the old cosmological constant problem: this is done in a
consistent way hinted by S. Weinberg in his comment concerning the question of
how one can avoid his no-go theorem. b) The power law inflation without any
fine tuning may end with damped oscillations of around the state with
zero cosmological constant. c) There are regions of the parameters where the
equation-of-state w=p/\rho in the late time universe is w<-1 and w
asymptotically (as t\to\infty) approaches -1 from below. This effect is
achieved without any exotic term in the action. In a model with both \phi and
\upsilon fields, a scenario which resembles the hybrid inflation is realized
but there are essential differences, for example: the Higgs field undergos
transition to a gauge symmetry broken phase \neq 0 soon after the end
of a power law inflation; there are two oscillatory regimes of \upsilon, one
around \upsilon =0 at 50 e-folding before the end of inflation, another -
during transition to a gauge symmetry broken phase where the scalar dark energy
density approaches zero without fine tuning; the gauge symmetry breakdown is
achieved without tachyonic mass term in the action.Comment: 47 pages, 28 figure
Is Cosmic Coincidence a Consequence of a Law of Nature?
A field theory is proposed where the regular fermionic matter and the dark
fermionic matter are different states of the same "primordial" fermion fields.
In regime of the fermion densities typical for normal particle physics, the
primordial fermions split into three families identified with regular fermions.
When fermion energy density becomes comparable with dark energy density, the
theory allows new type of states. The possibility of such Cosmo-Low Energy
Physics (CLEP) states is demonstrated by means of solutions of the field theory
equations describing FRW universe filled by homogeneous scalar field and
uniformly distributed nonrelativistic neutrinos. Neutrinos in CLEP state are
drawn into cosmological expansion by means of dynamically changing their own
parameters. One of the features of the fermions in CLEP state is that in the
late time universe their masses increase as a^{3/2}. The energy density of the
cold dark matter consisting of neutrinos in CLEP state scales as a sort of dark
energy; this cold dark matter possesses negative pressure and for the late time
universe its equation of state approaches that of the cosmological constant.
The total energy density of such universe is less than it would be in the
universe free of fermionic matter at all. The (quintessence) scalar field is
coupled to dark matter but its coupling to regular fermionic matter appears to
be extremely strongly suppressed. The key role in obtaining these results
belongs to a fundamental constraint (which is consequence of the action
principle) that plays the role of a new law of nature.Comment: 26 pages; some typos correcte
Geometrical Origin of Fermion Families in SU(2)xU(1) Gauge Theory
A spontaneously broken SU(2)xU(1) gauge theory with just one "primordial"
generation of fermions is formulated in the context of generally covariant
theory which contains two measures of integration in the action: the standard
\sqrt{-g}d^{4}x and a new \Phi d^{4}x, where \Phi is a density built out of
degrees of freedom independent of the metric. Such type of models are known to
produce a satisfactory answer to the cosmological constant problem. Global
scale invariance is implemented. After SSB of scale invariance and gauge
symmetry it is found that with the conditions appropriate to laboratory
particle physics experiments, to each primordial fermion field corresponds
three physical fermionic states. Two of them correspond to particles with
constant masses and they are identified with the first two generations of the
electro-weak theory. The third fermionic states at the classical level get
non-polynomial interactions which indicate the existence of fermionic
condensate and fermionic mass generation.Comment: LATEX, 8 pages; misprint correcte
Interactions from SSB of scale symmetry: applications to problems of quintessence, galaxy dark matter and fermion family
We study a scale invariant two measures theory where a dilaton field \phi has
no explicit potentials. The scale transformations include a shift
\phi\to\phi+const. The theory demonstrates a new mechanism for generation of
the exponential potential: in the conformal Einstein frame (CEF), after SSB of
scale invariance, the theory develops the exponential potential and, in
general, non-linear kinetic term is generated as well. The possibility of
quintessence and of halo dark matter solutions are shown. The regime where the
fermionic matter dominates (as compared to the dilatonic contribution) is
analyzed. There it is found that starting from a single fermionic field we
obtain exactly three different types of spin 1/2 particles in CEF that appears
to suggest a new approach to the family problem of particle physics. It is
automatically achieved that for two of them, fermion masses are constants,
gravitational equations are canonical and the "fifth force" is absent. For the
third type of particles, four fermionic interaction appears from SSB of scale
invariance.Comment: latex, 14 page
New physics at low energies and dark matter-dark energy transmutation
A field theory is proposed where the regular fermionic matter and the dark
fermionic matter can be different states of the same "primordial" fermion
fields. In regime of the fermion densities typical for normal particle physics,
the primordial fermions split into three families identified with regular
fermions. When fermion energy density becomes comparable with dark energy
density, the theory allows transition to new type of states. The possibility of
such Cosmo-Low Energy Physics (CLEP) states is demonstrated by means of
solutions of the field theory equations describing FRW universe filled with
homogeneous scalar field and uniformly distributed nonrelativistic neutrinos.
Neutrinos in CLEP state are drawn into cosmological expansion by means of
dynamically changing their own parameters. One of the features of the fermions
in CLEP state is that in the late time universe their masses increase as
a^{3/2} (a=a(t) is the scale factor). The energy density of the cold dark
matter consisting of neutrinos in CLEP state scales as a sort of dark energy;
this cold dark matter possesses negative pressure and for the late time
universe its equation of state approaches that of the cosmological constant.
The total energy density of such universe is less than it would be in the
universe free of fermionic matter at all.Comment: Contribution to Coral Gables Conference 2003 on High-Energy Physics
and Cosmology; 8 page
Field Theory Models without the Cosmological Constant Problem
We study field theory models in the context of a gravitational theory based
on the requirement that the measure of integration in the action is not
necessarily \sqrt{-g} but it is determined dynamically through additional
degrees of freedom, like four scalar fields \phi_{a}. We study three
possibilities for the general structure of the theory: (A) The total action has
the form S=\int\Phi Ld^{4}x where the measure \Phi is built from the scalars
\phi_{a} in such a way that the transformation L\to L+const does not effect
equations of motion. Then an infinite dimensional shifts group of the measure
fields (SGMF) \phi_{a} by arbitrary functions of the Lagrangian density L is a
symmetry group of the action. (B) The total action has the form S=S_{1}+S_{2},
S_{1}=\int\Phi L_{1}d^{4}x, S_{2}=\int\sqrt{-g}L_{2}d^{4}x which is the only
model different from (A) and invariant under SGMF (but now with f_{a}=
f_{a}(L_{1})). Similarly, now only S_{1} satisfies the requirement that the
transformation L_{1}\to L_{1}+const does not effect equations of motion. Both
in the case (A) and in the case (B) it is assumed that L, L_{1}, L_{2} do not
depend on \phi_{a}. (C) The action includes a term which breaks the SGMF
symmetry. It is shown that in the first order formalism in cases (A) and (B)
the CCP is solved: the effective potential vanishes in a true vacuum state
(TVS) without fine tuning. In the case (C), the breaking of the SGMF symmetry
induces a nonzero energy density for the TVS.Comment: Plenary talk given by E.I.Guendelman in the Fourth Alexander
Friedmann International Seminar on Gravitation and Cosmology, St. Petersburg,
1998; 25 pages. LaTe
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