275 research outputs found
Field theory model giving rise to "quintessential inflation" without the cosmological constant and other fine tuning problems
A field theory is developed based on the idea that the effective action of
yet unknown fundamental theory, at energy scale below M_{p} has the form of
expansion in two measures: S=\intd^{4}x[\Phi L_{1}+\sqrt{-g}L_{2}] where the
new measure \Phi is defined using the third-rank antisymmetric tensor. In the
new variables (Einstein frame) all equations of motion take canonical GR form
and therefore models are free of the well-known "defects" that distinguish the
Brans-Dicke type theories from GR. All novelty is revealed only in an unusual
structure of the effective potential U(\phi) and interactions which turns over
intuitive ideas based on our experience in field theory. E.g. the greater
\Lambda we admit in L_{2}, the smaller U(\phi) will be in the Einstein picture.
Field theory models are suggested with explicitly broken global continuos
symmetry which in the Einstein frame has the form \phi\to\phi+const. The
symmetry restoration occurs as \phi\to\infty. A few models are presented where
U is produced with the following shape: for \phi<-M_{p}, U has the form typical
for inflation model, e. g. U=\lambda\phi^4 with \lambda\sim 10^{-14};
for\phi>-M_{p}, U has mainly exponential form U\sim e^{-a\phi/M_{p}} with
variable a: a=14 for -M_{p}<\phi<M_{p} that admits nucleosynthesis; a=2 for
\phi>M_{p} that implies quintessence era. There is no need in any fine tuning
to prevent appearance of the CC term or any other terms that could violate
flatness of U at \phi\ggM_{p}. \lambda\sim 10^{-14} is obtained without fine
tuning as well. Quantized matter fields models, including gauge theories with
SSB can be incorporated without altering mentioned above results. Direct
fermion-inflaton coupling resembles Wetterich's model but it does not lead to
any observable effect at present. SSB does not raise any problem with CC.Comment: REVTeX, shorter version (23 pages instead of 33), more convenient for
readin
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
Gravity, Cosmology and Particle Physics without the Cosmological Constant Problem
This essay elucidates recent achievements of the "nongravitating vacuum
energy" (NGVE) theory" which has the feature that a shift of the Lagrangian
density by a constant does not affect dynamics. In the first order formalism, a
constraint appears that enforces the vanishing of the cosmological constant
\Lambda. Standard dynamics of gauge unified theories (including fermions) and
their SSB appear if a four index field strength condensate is present. At a
vacuum state there is 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 \Lambda problem with inflation and transition to a \Lambda =0
phase without fine tuning after a reheating period. The model opens new
possibilities for a solution of the hierarchy problem.Comment: 7 pages, received an "honorable mention" from Gravity Research
Foundation, 199
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
SSB of scale symmetry, fermion families and quintessence without the long-range force problem
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 gene- ration 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 solutions are shown. As an example, for one choice of the
parameters we obtain standard scaling solutions usually used in the context of
the quintessential scenario. For other choice of the parameters, the theory
allows a scaling solution with equation of state p_{\phi}=w\rho_{\phi} where w
is restricted by -1<w<-0.82. 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, a fermionic
self-interaction appears as a result of SSB of scale invariance.Comment: latex, 25 pages; misprint correcte
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