The OPERA neutrinos had energies of about 17 gigaelectron volts. "They had a lot of energy but very little mass," Cowsik says, "so they should go very fast." The question is whether they went faster than the speed of light.

"We've shown in this paper that if the neutrino that comes out of a pion decay were going faster than the speed of light, the pion lifetime would get longer, and the neutrino would carry a smaller fraction of the energy shared by the neutrino and the muon," Cowsik says.

"What's more," he says, "these difficulties would only increase as the pion energy increases.

"So we are saying that in the present framework of physics, superluminal neutrinos would be difficult to produce," Cowsik explains.

In addition, he says, there's an experimental check on this theoretical conclusion. The creation of neutrinos at CERN is duplicated naturally when cosmic rays hit Earth's atmosphere.

A neutrino observatory called IceCube detects these neutrinos when they collide with other particles generating muons that leave trails of light flashes as they plow into the thick, clear ice of Antarctica.

"IceCube has seen neutrinos with energies 10,000 times higher than those the OPERA experiment is creating," Cowsik says.."Thus, the energies of their parent pions should be correspondingly high. Simple calculations, based on the conservation of energy and momentum, dictate that the lifetimes of those pions should be too long for them ever to decay into superluminal neutrinos.

"But the observation of high-energy neutrinos by IceCube indicates that these high-energy pions do decay according to the standard ideas of physics, generating neutrinos whose speed approaches that of light but never exceeds it.

Cowsik's objection to the OPERA results isn't the only one that has been raised.