DOI: 10.1051/0004-6361/200911881

## The residual gravity acceleration effect in the Poincaré dodecahedral space

**B. F. Roukema and P. T. Różański**

Toruń Centre for Astronomy, Nicolaus Copernicus University, ul. Gagarina 11, 87-100 Toruń, Poland

Received 19 February 2009 / Accepted 17 March 2009

** Abstract ***Context. *In a flat space, it has been shown heuristically that the global topology of comoving space can affect the dynamics expected in the weak-field Newtonian limit, inducing a weak acceleration effect similar to dark energy.*Aims. *Does a similar effect occur in the case of the Poincaré dodecahedral space, which is a candidate model of comoving space for solving the missing fluctuations problem observed in cosmic microwave background all-sky maps? Moreover, does the effect distinguish the Poincaré space from other well-proportioned spaces?*Methods. *The acceleration effect in the Poincaré space *S*^{3}/*I*^{*} is studied, using a massive particle and a nearby test particle of negligible mass. Calculations are made in *S*^{3} embedded in
. The weak-limit gravitational attraction on a test particle at distance *r* is set to be
rather than
, where
is the curvature radius, in order to satisfy Stokes' theorem. A finite particle horizon large enough to include the adjacent topological images of the massive particle is assumed. The regular, flat, 3-torus *T*^{3} is re-examined, and two other well-proportioned spaces, the octahedral space *S*^{3}/*T*^{*}, and the truncated cube space *S*^{3}/*O*^{*}, are also studied.*Results. *The residual gravity effect occurs in all four cases. In a perfectly regular 3-torus of side length *L*_{a}, and in the octahedral and truncated cube spaces, the highest order term in the residual acceleration is the third-order term in the Taylor expansion in powers of *r*/*L*_{a} (3-torus), or
, respectively. However, the Poincaré dodecahedral space is unique among the four spaces. The third order cancels, leaving the fifth order term
as the
most significant.*Conclusions. *Not only are three of the four perfectly regular well-proportioned spaces better balanced than most other multiply connected spaces in terms of the residual gravity acceleration effect by a factor of
about a million (setting *r*/*L*_{a} =
~ 10^{-3}), but the fourth of these spaces is about ten thousand times better balanced than the other three. This is the Poincaré dodecahedral space. Is this unique dynamical property of the Poincaré space a clue towards a theory of cosmic topology?

**Key words:**cosmology: theory

**--**cosmological parameters

**--**large-scale structure of Universe

**--**early Universe

**©**

*ESO 2009*