Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Natural solution to the naturalness problem -- Universe does fine-tuning   We propose a new mechanism to solve the fine-tuning problem. We start from a
multi-local action $
S=\sum_{i}c_{i}S_{i}+\sum_{i,j}c_{i,j}S_{i}S_{j}+\sum_{i,j,k}c_{i,j,k}S_{i}S_{j}S_{k}+\cdots$,
where $S_{i}$'s are ordinary local actions. Then, the partition function of
this system is given by \begin{equation} Z=\int d\overrightarrow{\lambda}
f(\overrightarrow{\lambda})\langle
f|T\exp\left(-i\int_{0}^{+\infty}dt\hat{H}(\overrightarrow{\lambda};a_{cl}(t))\right)|i\rangle,\nonumber\end{equation}
where $\overrightarrow{\lambda}$ represents the parameters of the system whose
Hamiltonian is given by $\hat{H}(\overrightarrow{\lambda};a_{cl}(t))$,
$a_{cl}(t)$ is the radius of the universe determined by the Friedman equation,
and $f(\overrightarrow{\lambda})$, which is determined by $S$, is a smooth
function of $\overrightarrow{\lambda}$. If a value of
$\overrightarrow{\lambda}$, $\overrightarrow{\lambda}_{0}$, dominates in the
integral, we can interpret that the parameters are dynamically tuned to
$\overrightarrow{\lambda}_{0}$. We show that indeed it happens in some
realistic systems. In particular, we consider the strong CP problem, multiple
point criticality principle and cosmological constant problem. It is
interesting that these different phenomena can be explained by one mechanism.

11
The categories of this paper are: hep-lat
9
The categories of this paper are: nlin
30
The categories of this paper are: q-alg
10
The categories of this paper are: q-bio
21
The categories of this paper are: adap-org
29
The categories of this paper are: funct-an
1
The categories of this paper are: cs
23
The categories of this paper are: solv-int
4
The categories of this paper are: cond-mat
28
The categories of this paper are: alg-geom
8
The categories of this paper are: hep-ex
35
The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex
3
The categories of this paper are: physics
34
The categories of this paper are: chem-ph
12
The categories of this paper are: nucl-th