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Testing the Dark Energy Paradigm and Measuring Neutrino Mass with the Dark Energy Survey

Final Report Summary - TESTDE (Testing the Dark Energy Paradigm and Measuring Neutrino Mass with the Dark Energy Survey)

The TESTDE Project is focused on “Testing the Dark Energy Paradigm and Measuring Neutrino Mass with the Dark Energy Survey”. It resulted in over 170 publications co-authored by TESTDE members, about 30 papers of them led by our team.

One of the greatest mysteries in the whole of science is that 70% of the Universe appears to be made of an enigmatic ‘Dark Energy’. A further 25% of the Universe is made from invisible ‘Cold Dark Matter’ that can only be detected through its gravitational effects, with the ordinary atomic matter making up only 5% of the total cosmic budget. These discoveries require a shift in our perception. I have played leadership roles in several large surveys, in particular the $40M international Dark Energy Survey (DES), where I co-chaired the entire science programme (2006-2016), with 400 scientists from 7 countries.

DES had its first light in September in 2012, and the five planned seasons (2013-2018) are now complete. The DES data has been key to exploring the three interlinked TESTDE project themes:

*Theme 1: Combined probes of Dark Energy and Modified Gravity from DES and DESI
*Theme 2: Neutrino masses from Cosmology
*Theme 3: Photometric Redshifts and their Impact for Cosmic Probes

The highlights are:
• Based a combination of the three Themes and work by others in the DES collaboration, DES results so far strongly favour a present day universe with Dark Energy in the form of a Cosmological Constant (70%) + Cold Dark Matter (25%) and baryons (5%), with much better accuracy and precision than previously known from galaxy surveys.

• The Neutrino mass upper limit has been improved, down to 0.26 eV, but not detected yet. This is a major challenge for the DES final analysis.

• An unexpected and exciting spin-off of the TEDTDE project is the optical DES camera followup of the LIGO Gravitational Wave Binary Neutron Star (BNS) GW170817. Members of our TESTDE team led a study of the host galaxy NGC4993, proposing that its shell strcuture may indicate the galaxy merger, with implications for the formation of the BNS.