invariance

Do neutrinos of different flavors have different preferred directions? If so, this would mean that Lorentz invariance is violated, something that is posited by some theories of quantum gravity. In them, Lorentz-invariance violation (LIV) would become more prominent the higher the energies involved.

Motivated by this, we look for signs of this flavor-dependent LIV using the high-energy astrophysical neutrinos seen by IceCube, with energies in the TeV-PeV range.

If LIV exists, the neutrinos would be affected by their interaction with a pervasive LIV field that couples differently to different neutrino flavors. As a result, the sky distributions of high-energy astrophysical electron, muon, and tau neutrinos arriving at Earth would be anisotropic.

In a new paper led by PhD student Bernanda Telalovic, we look for these high-energy neutrino flavor anisotropies in IceCube data, specifically, in the public 7.5-year sample of High-Energy Starting Events (HESE). We do this using the methods introduced in an earlier paper of ours (2310.15224).

We find no evidence for the patterns of flavor anisotropy expected from LIV, and so we place new upper limits on hundreds of parameters regulating Lorentz-invariance violation within the Standard Model Extension. We explore LIV operator dimensions from 2 to 8, each with a different dependence on neutrino energy and introducing different forms of flavor anisotropy.

For many of them, we improve upon existing limits—on account of using higher energies—or place limits for the first time ever:

Our new upper limits on the LIV parameters are available in digital form for download at 68%, 95%, and 99% C.L. GitHub, here.

Read more at:

No Flavor Anisotropy in the High-Energy Neutrino Sky Upholds Lorentz Invariance
Bernanda Telalovic, Mauricio Bustamante
2503.15468 astro-ph

Lorentz invariance is one of the pillars of modern physics, underlying special relativity—and, with that, the Standard Model—and general relativity. It posits that the laws of physics are the same for all observers moving in their own inertial frame. Yet, at high energies and short distances, Lorentz invariance may no longer hold.

To date, Lorentz invariance remains unbroken in all experimental tests. If it were violated, however, it could have many and varied consequences. Accordingly, there have been multiple searches for Lorentz invariance violation, using atom interferometry, gamma rays, cosmic rays, and neutrinos, etc. See, for instance, the data tables in 0801.0287.

High-energy astrophysical neutrinos, with TeV-PeV, are powerful probes of Lorentz invariance, thanks to their high energies and long traveled distances from their sources to Earth, of Mpc-Gpc scales. If Lorentz invariance is violated, it could imply that, en route to Earth, higher-energy neutrinos would travel more slowly than lower-energy neutrinos.

In a new paper, we introduce methods to look for these temporal distortions. We use the high-energy joint time and energy distribution of the neutrino flare detected by IceCube in 2014/2015 from the blazar TXS 0506+056 to look for specific signatures from Lorentz-invariance violation. We do this by borrowing non-parametric statistical methods previously used to look for signs of Lorentz-invariance violation in the gamma rays from gamma-ray bursts (1807.00189).

And, in doing so, we account for the significant energy and directional uncertainty associated to the detection of high-energy astrophysical neutrinos. Doing this makes our analysis realistic and robust, even if it erodes some of its sensitivity.

As a result, we set new lower limits on the energy scale of Lorentz-invariance violation in neutrino propagation. If Lorentz invariance is broken, this must happen at energies beyond 10^{14} GeV, if the effects depend linearly on the neutrino energy, or beyond 10^9 GeV, if they depend quadratically on it.

Mauricio Bustamante

Associate Professor – Niels Bohr Institute, University of Copenhagen

No Flavor Anisotropy in the High-Energy Neutrino Sky Upholds Lorentz Invariance

Testing Lorentz invariance with a flare of high-energy astrophysical neutrinos