  It has been pointed out recently that the presence of dilaton field in the
early Universe can dilute the neutralino dark matter (DM) abundance, if
Universe is not radiation dominated at DM decoupling, due to its
dissipative-like coupling to DM. In this scenario two basic mechanisms compete,
the modified Hubble expansion rate tending to increase the relic density and a
dissipative force that tends to decrease it. The net effect can lead to an
overall dramatic decrease of the predicted relic abundance, sometimes by
amounts of the order of O(10^2) or so. This feature is rather generic,
independent of any particular assumption on the underlying string dynamics,
provided dilaton dominates at early eras after the end of inflation but before
Big Bang Nucleosynthesis (BBN). The latter ensures that BBN is not upset by the
presence of the dilaton. In this paper, within the context of such a scenario,
we study the phenomenology of the constrained minimal supersymmetric model
(CMSSM) by taking into account all recent experimental constraints, including
those from the LHC searches. We find that the allowed parameter space is
greatly enlarged and includes regions that are beyond the reach of LHC. The
allowed regions are compatible with Direct Dark Matter searches since the small
neutralino annihilation rates, that are now in accord with the cosmological
data on the relic density, imply small neutralino-nucleon cross sections below
the sensitivities of the Direct Dark Matter experiments. It is also important
that the new cosmologically accepted regions are compatible with Higgs boson
masses larger than 120 GeV, as it is indicated from the LHC experimental data.
The smaller annihilation cross sections needed to explain WMAP data require
that the detector performances of current and planned indirect DM search
experiments through gamma rays should be greatly improved in order to probe the
CMSSM regions.
