Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Vacuum Fluctuations of Energy Density can lead to the observed
  Cosmological Constant   The energy density associated with Planck length is $\rho_{uv}\propto
L_P^{-4}$ while the energy density associated with the Hubble length is
$\rho_{ir}\propto L_H^{-4}$ where $L_H=1/H$. The observed value of the dark
energy density is quite different from {\it either} of these and is close to
the geometric mean of the two: $\rho_{vac}\simeq \sqrt{\rho_{uv} \rho_{ir}}$.
It is argued that classical gravity is actually a probe of the vacuum {\it
fluctuations} of energy density, rather than the energy density itself. While
the globally defined ground state, being an eigenstate of Hamiltonian, will not
have any fluctuations, the ground state energy in the finite region of space
bounded by the cosmic horizon will exhibit fluctuations $\Delta\rho_{\rm
vac}(L_P, L_H)$. When used as a source of gravity, this $\Delta \rho$ should
lead to a spacetime with a horizon size $L_H$. This bootstrapping condition
leads naturally to an effective dark energy density $\Delta\rho\propto
(L_{uv}L_H)^{-2}\propto H^2/G$ which is precisely the observed value. The model
requires, either (i) a stochastic fluctuations of vacuum energy which is
correlated over about a Hubble time or (ii) a semi- anthropic interpretation.
The implications are discussed.

31
The categories of this paper are: ao-sci
20
The categories of this paper are: acc-phys
16
The categories of this paper are: stat
32
The categories of this paper are: atom-ph
25
The categories of this paper are: patt-sol
12
The categories of this paper are: nucl-th
36
The categories of this paper are: cmp-lg
9
The categories of this paper are: nlin
22
The categories of this paper are: chao-dyn
17
The categories of this paper are: q-fin
26
The categories of this paper are: bayes-an
8
The categories of this paper are: hep-ex
21
The categories of this paper are: adap-org
2
The categories of this paper are: math
23
The categories of this paper are: solv-int
18
The categories of this paper are: econ