[Paper Review] EuCAPT White Paper: Opportunities and Challenges for Theoretical Astroparticle Physics in the Next Decade

Rafael Alves Batista, Mustafa A. Amin+135 more|arXiv (Cornell University)|Jan 1, 2021

Astrophysics and Cosmic Phenomena1,329 references43 citations

TL;DR

This white paper, authored by EuCAPT, synthesizes the theoretical challenges and opportunities in astroparticle physics over the next decade, emphasizing multi-messenger synergies across neutrinos, gravitational waves, and electromagnetic signals. It outlines transformative potential from upcoming observatories and proposes a coordinated theoretical framework to address fundamental questions like dark matter, neutrino masses, and the nature of cosmic inflation.

ABSTRACT

Astroparticle physics is undergoing a profound transformation, due to a series of extraordinary new results, such as the discovery of high-energy cosmic neutrinos with IceCube, the direct detection of gravitational waves with LIGO and Virgo, and many others. This white paper is the result of a collaborative effort that involved hundreds of theoretical astroparticle physicists and cosmologists, under the coordination of the European Consortium for Astroparticle Theory (EuCAPT). Addressed to the whole astroparticle physics community, it explores upcoming theoretical opportunities and challenges for our field of research, with particular emphasis on the possible synergies among different subfields, and the prospects for solving the most fundamental open questions with multi-messenger observations.

Motivation & Objective

• To identify and prioritize the most pressing theoretical challenges in astroparticle physics over the next decade.
• To map synergies between subfields—neutrino physics, gravitational wave astronomy, dark matter, and cosmology—through multi-messenger observations.
• To guide the development of theoretical frameworks that can interpret and predict results from next-generation experiments and observatories.
• To address fundamental open questions such as the nature of dark matter, the origin of cosmic neutrino fluxes, and the physics of the early universe.
• To promote interdisciplinary collaboration across theoretical astrophysics, particle physics, and cosmology to maximize scientific impact from upcoming data.

Proposed method

• Synthesizing input from over 300 theoretical astroparticle physicists and cosmologists across Europe and beyond.
• Systematically evaluating the theoretical implications of recent discoveries, including high-energy neutrinos (IceCube), gravitational waves (LIGO/Virgo), and cosmic microwave background anisotropies.
• Integrating predictions from quantum field theory, general relativity, and effective field theories to model dark matter, dark energy, and neutrino interactions.
• Projecting theoretical expectations for upcoming missions such as LISA, CTA, DUNE, Einstein Telescope, and the James Webb Space Telescope.
• Using multi-messenger consistency checks to constrain models of compact object formation, phase transitions in the early universe, and new physics beyond the Standard Model.
• Developing a coordinated roadmap for theoretical research that aligns with experimental and observational timelines and capabilities.

Experimental results

Research questions

• RQ1 How can theoretical models of dark matter be constrained by multi-messenger data from X-ray, gamma-ray, neutrino, and gravitational wave observations?
• RQ2 What are the implications of the observed high-energy cosmic neutrino flux for new physics beyond the Standard Model?
• RQ3 How can gravitational wave observations of binary neutron star mergers and black hole systems inform theories of dense matter and strong-field gravity?
• RQ4 What theoretical frameworks best explain the origin and properties of the cosmic microwave background anomalies and their connection to early-universe physics?
• RQ5 How can effective field theories and symmetry principles be used to unify descriptions of dark energy, dark matter, and inflationary dynamics?

Key findings

• The discovery of high-energy astrophysical neutrinos by IceCube has opened a new window into the non-thermal universe, demanding new theoretical models of particle acceleration in extreme environments.
• Gravitational wave detections by LIGO and Virgo have confirmed the existence of stellar-mass black hole binaries and neutron star mergers, providing strong constraints on alternative gravity theories and compact object equations of state.
• Multi-messenger observations—especially from joint neutrino, gamma-ray, and gravitational wave detections—can significantly improve the localization and identification of cosmic sources.
• Theoretical models of dark matter must now account for constraints from direct detection experiments (e.g., XENONnT, LZ), indirect detection (Fermi-LAT), and collider searches, with increasing pressure on weakly interacting massive particle (WIMP) and axion-like particle scenarios.
• The next generation of observatories—including LISA, CTA, DUNE, and the Einstein Telescope—will enable precision tests of general relativity, probe the nature of dark energy, and potentially detect primordial gravitational waves from inflation.
• Synergistic analysis across subfields is essential: for example, combining neutrino data with X-ray and gamma-ray observations can resolve ambiguities in source identification and emission mechanisms.