Ripples in Cosmic Neutrino Background Measured for the First Time

Press Release From: University of Oxford
Posted: Wednesday, June 15, 2005


Astrophysicists from the Universities of Oxford and Rome have for the first time found evidence of ripples in the Universe's primordial sea of neutrinos, confirming the predictions of both Big Bang theory and the Standard Model of particle physics.

Neutrinos are elementary particles with no charge and very little mass, which are extremely difficult to study due to their very weak interaction with matter. Yet pinning down the physical properties of neutrinos is of paramount importance to scientists attempting to understand the fundamental building blocks of Nature. According to the standard Big Bang model, neutrinos permeate the Universe at a density of about 150 per cubic centimetre. The Earth is therefore immersed in an ocean of neutrinos, without us ever noticing.

Although it is impossible to measure this "Cosmic Neutrino Background" directly with present-day technology, physicists predict that ripples or waves in it have an impact on the growth of structures in the Universe.

In research to be published in the journal Physical Review Letters, Dr. Roberto Trotta, Lockyer Fellow of the Royal Astronomical Society at Oxford's Department of Physics, and Dr. Alessandro Melchiorri of La Sapienza University in Rome were able to demonstrate for the first time the existence of ripples of primordial origin in the Cosmic Neutrino Background.

The discovery, made by combining data produced by the NASA WMAP (Wilkinson Microwave Anisotropy Probe) satellite and the Sloan Digital Sky Survey, confirms the predictions of both the Big Bang theory and the Standard Model of particle physics. The research has important implications for the study of neutrinos, showing that theories of the infinitely large (cosmology) and the infinitely small (particle physics) are in agreement.

Dr. Trotta said: "This research provides important new evidence in favour of the current cosmological model, unifying it with fundamental physics theories. Cosmology is becoming a more and more powerful laboratory where physics not easily accessible on Earth can be tested and verified. The high quality of recent cosmological data allows us to investigate neutrinos in the cosmological framework, obtaining measurements which are competitive with -- if not superior to -- particle accelerator findings."


The paper "Indication for Primordial Anisotropies in the Neutrino Background from WMAP and SDSS" by Roberto Trotta and Alessandro Melchiorri has been accepted for publication in Physical Review Letters. A pre-print version of the article can be downloaded from:

High resolution images are available at:

WMAP is a NASA Explorer mission measuring the temperature of the cosmic background radiation over the full sky with unprecedented accuracy. This map of the remnant heat from the Big Bang provides answers to fundamental questions about the origin and fate of the Universe. For more information see The Sloan Digital Sky Survey, conducted using telescopes at the Apache Point Observatory in the US, aims to systematically map one-quarter of the entire sky, producing a detailed image of it and determining the positions and absolute brightnesses of more than 100 million celestial objects. It will also measure the distances to more than a million galaxies and quasars. For more information see


Dr. Roberto Trotta (out of the office Wednesday and Friday)
Lockyer Fellow of the Royal Astronomical Society
University of Oxford, Astrophysics Dept.
Denys Wilkinson Building
Keble Road
Oxford, OX1 3RH
Phone: +44 (0)1865-283016
Mobile: +44 (0)7765-807509

Dr. Alessandro Melchiorri
Universita di Roma "La Sapienza"
Sezione INFN di Roma
Ple Aldo Moro
00185 Roma, Italy
Phone: +39 06 49914052

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