Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The fractal structure of the universe : a new field theory approach   While the universe becomes more and more homogeneous at large scales,
statistical analysis of galaxy catalogs have revealed a fractal structure at
small-scales (\lambda < 100 h^{-1} Mpc), with a fractal dimension D=1.5-2
(Sylos Labini et al 1996). We study the thermodynamics of a self-gravitating
system with the theory of critical phenomena and finite-size scaling and show
that gravity provides a dynamical mechanism to produce this fractal structure.
We develop a field theoretical approach to compute the galaxy distribution,
assuming them to be in quasi-isothermal equilibrium. Only a limited, (although
large), range of scales is involved, between a short-distance cut-off below
which other physics intervene, and a large-distance cut-off, where the thermo-
dynamic equilibrium is not satisfied. The galaxy ensemble can be considered at
critical conditions, with large density fluctuations developping at any scale.
  From the theory of critical phenomena, we derive the two independent critical
exponents nu and eta and predict the fractal dimension D = 1/nu to be either
1.585 or 2, depending on whether the long-range behaviour is governed by the
Ising or the mean field fixed points, respectively. Both set of values are
compatible with present observations. In addition, we predict the scaling
behaviour of the gravitational potential to be r^{-(1 + eta)/2}. That is,
r^{-0.5} for mean field or r^{- 0.519} for the Ising fixed point. The theory
allows to compute the three and higher density correlators without any
assumption or Ansatz. We find that the N-points density scales as
r_1^{(N-1)(D-3)}, when r_1 >> r_i, 2 leq i leq N . There are no free parameters
in this theory.

31
The categories of this paper are: ao-sci
18
The categories of this paper are: econ
23
The categories of this paper are: solv-int
36
The categories of this paper are: cmp-lg
3
The categories of this paper are: physics
2
The categories of this paper are: math
24
The categories of this paper are: dg-ga
19
The categories of this paper are: eess
29
The categories of this paper are: funct-an
34
The categories of this paper are: chem-ph
13
The categories of this paper are: quant-ph
20
The categories of this paper are: acc-phys
37
The categories of this paper are: supr-con
32
The categories of this paper are: atom-ph
27
The categories of this paper are: comp-gas
15
The categories of this paper are: nucl-ex