We have proposed that the cosmic ray spectrum “ knee ” , the steepening of the cosmic ray spectrum at energy E \lower 2.15 pt \hbox { $ \buildrel > \over { \sim } $ } 10 ^ { 15.5 } eV , is due to “ new physics ” , namely new interactions at TeV cm energies which produce particles undetected by the experimental apparatus .
In this letter we examine specifically the possibility that this interaction is low scale gravity .
We consider that the graviton propagates , besides the usual four dimensions , into an additional \delta , compactified , large dimensions and we estimate the graviton production in p p collisions in the high energy approximation where graviton emission is factorized .
We find that the cross section for graviton production rises as fast as ( \sqrt { s } / M _ { f } ) ^ { 2 + \delta } , where M _ { f } is the fundamental scale of gravity in 4 + \delta dimensions , and that the distribution of radiating a fraction y of the initial particle ’ s energy into gravitational energy ( which goes undetected ) behaves as \delta y ^ { \delta - 1 } .
The missing energy leads to an underestimate of the true energy and generates a break in the inferred cosmic ray spectrum ( the “ knee ” ) .
By fitting the cosmic ray spectrum data we deduce that the favorite values for the parameters of the theory are M _ { f } \sim 8 TeV and \delta = 4 .