Next: Calculations of .
Up: One-loop approximation
Previous: One-loop approximation
In the one-loop approximation expression for
has the form
|
(79) |
where
is given by (A1-A3). Our
goal here is to analyze these expressions in one-pole approximation,
by substituting in it ``one-pole''
and
from (4.11) and (4.16). In the resulting
expression one can perform the integration over analytically.
The result is
Next we introduce
, with
given by (4.14) and consider (4.18) in the limit
of small , which allows us to perform analytically
integrations over perpendicular components of wavevectors. The result
for the damping frequency may be represented in the
following form (for details see Appendix B):
|
|
|
(81) |
We introduced here cut-off for small at , where is the
size of the box. We also introduced ``the density of the number of
particles'' in the solid angle according to
|
(82) |
such that the total number of particles
|
(83) |
After substituting from (B11), one has the following
estimate for
:
|
(84) |
Consider now
. It follows
from (B12) that
where
is the
``triad interaction'' frequency. One may evaluate the integral with
respect to as
|
(86) |
After substituting
from (4.22), one has
|
(87) |
The main contribution to the integral (4.23) over comes from
the infrared region . It gives the estimate,
|
(88) |
where we have defined the density of the wave energy in solid angle as
|
(89) |
This value relates to as follows:
|
(90) |
Equation (4.26) together with the expression (B11) for may
be written as
|
(91) |
where
|
(92) |
is the dimensionless parameter of nonlinearity, the ratio of energy of
acoustic turbulence and the density of thermal energy of media
, where is the concentration of
atoms.
Equation (4.22) for
may be written
in a similar form
|
(93) |
One can see that
|
(94) |
It means that for large enough inertial interval
|
(95) |
and one may neglect the nonlinear corrections
to
the frequency with respect to the damping of the waves
. That shows that our above calculations of
is
self-consistent. Later we also will take into account only damping
in the expressions for the Green's functions taking
.
Next: Calculations of .
Up: One-loop approximation
Previous: One-loop approximation
Dr Yuri V Lvov
2007-01-17