We estimate the constraints that the recent high-redshift sample of supernovae type Ia put on a phenomenological interaction between dark energy and dark matter .
The interaction can be interpreted as arising from the time variation of the mass of dark matter particles .
We find that the coupling correlates with the equation of state : roughly speaking , a negative coupling ( in our sign convention ) implies phantom energy ( w _ { \phi } < -1 ) while a positive coupling implies ‘ ‘ ordinary ’ ’ dark energy .
The constraints from the current supernovae Ia Hubble diagram favour a negative coupling and an equation of state w _ { \phi } < -1 .
A zero or positive coupling is in fact unlikely at 99 % c.l .
( assuming constant equation of state ) ; at the same time non-phantom values ( w _ { \phi } > -1 ) are unlikely at 95 % .
We show also that the usual bounds on the energy density weaken considerably when the coupling is introduced : values as large as \Omega _ { m 0 } = 0.7 become acceptable for as concerns SNIa .
We find that the rate of change of the mass \dot { m } / m of the dark matter particles is constrained to be \delta _ { 0 } in a Hubble time , with -10 < \delta _ { 0 } < -1 to 95 % c.l.. We show that a large positive coupling might in principle avoid the future singularity known as ‘ ‘ big rip ’ ’ ( occurring for w _ { \phi } < -1 ) but the parameter region for this to occur is almost excluded by the data .
We also forecast the constraints that can be obtained from future experiments , focusing on supernovae and baryon oscillations in the power spectra of deep redshift surveys .
We show that the method of baryon oscillations holds the best potential to contrain the coupling .