We give a fresh look at the WIMP paradigm by considering updated limits and prospects for direct and indirect dark matter detection and covering realistic dark matter models, beyond the so-called simplified models, which have been the target of experimental scrutiny. In particular, we investigate dark matter scenarios featuring dwindled direct detection signals, due to loop or momentum suppression. Therefore, this review extends previous reviews in different aspects and motivates the search for WIMP dark matter in light of the present and near-future detectors.

Italy

Giorgio Arcadi

Spain

David Cabo-Almeida

United States

Maíra Dutra

India

Pradipta Ghosh

Germany

Manfred Lindner

France

Yann Mambrini

Brazil

Jacinto Neto

Mathias Pierre

Stefano Profumo

Chile

Farinaldo Queiroz

The waning of the WIMP: endgame?

The Pierre Auger Collaboration has embraced the concept of open access to their research data since its foundation, with the aim of giving access to the widest possible community. A gradual process of release began as early as 2007 when 1% of the cosmic-ray data was made public, along with 100% of the space-weather information. In February 2021, a portal was released containing 10% of cosmic-ray data collected by the Pierre Auger Observatory from 2004 to 2018, during the first phase of operation of the Observatory. The Open Data Portal includes detailed documentation about the detection and reconstruction procedures, analysis codes that can be easily used and modified and, additionally, visualization tools. Since then, the Portal has been updated and extended. In 2023, a catalog of the highest-energy cosmic-ray events examined in depth has been included. A specific section dedicated to educational use has been developed with the expectation that these data will be explored by a wide and diverse community, including professional and citizen scientists, and used for educational and outreach initiatives. This paper describes the context, the spirit, and the technical implementation of the release of data by the largest cosmic-ray detector ever built and anticipates its future developments.

Australia

A. Abdul Halim

Portugal

P. Abreu

M. Aglietta

Argentina

I. Allekotte

Netherlands

K. Almeida Cheminant

A. Almela

R. Aloisio

J. Alvarez-Muñiz

A. Ambrosone

J. Ammerman Yebra

G. Anastasi

L. Anchordoqui

B. Andrada

L. Andrade Dourado

S. Andringa

L. Apollonio

C. Aramo

P. Araújo Ferreira

E. Arnone

Mexico

J. Arteaga Velázquez

P. Assis

G. Avila

E. Avocone

Czechia

A. Bakalova

F. Barbato

A. Bartz Mocellin

J. Bellido

C. Berat

M. Bertaina

X. Bertou

M. Bianciotto

P. Biermann

V. Binet

K. Bismark

T. Bister

J. Biteau

J. Blazek

C. Bleve

J. Blümer

M. Boháčová

D. Boncioli

C. Bonifazi

L. Bonneau Arbeletche

Poland

N. Borodai

J. Brack

P. Brichetto Orchera

F. Briechle

A. Bueno

Belgium

S. Buitink

M. Buscemi

M. Büsken

A. Bwembya

K. Caballero-Mora

S. Cabana-Freire

L. Caccianiga

F. Campuzano

R. Caruso

A. Castellina

F. Catalani

G. Cataldi

L. Cazon

M. Cerda

B. Čermáková

A. Cermenati

J. Chinellato

J. Chudoba

L. Chytka

R. Clay

A. Cobos Cerutti

R. Colalillo

R. Conceição

A. Condorelli

G. Consolati

M. Conte

F. Convenga

D. Correia dos Santos

P. Costa

C. Covault

M. Cristinziani

C. Cruz Sanchez

S. Dasso

K. Daumiller

B. Dawson

R. Almeida

B. Errico

J. Jesús

S. Jong

J. Mello Neto

I. Mitri

J. Oliveira

D. Oliveira Franco

F. Palma

V. Souza

E. Vito

A. Popolo

O. Deligny

N. Denner

L. Deval

A. Matteo

C. Dobrigkeit

The Pierre Auger Observatory open data

It is assumed that superheavy dark matter particles with O(EeV) mass may decay to relativistic milli-charged particles (MCPs). The upward-going MCPs passing through the Earth can be measured by the fluorescence detectors (FD) of the Pierre Auger observatory (Auger). The massless hidden photon model is taken for MCPs to interact with nuclei, so that the numbers and fluxes of expected MCPs may be evaluated at the FD of Auger. Based on the assumption that no events are observed at the FD of Auger in 14 years, the corresponding upper limits on MCP fluxes are calculated at 90% C. L. These results indicate that MCPs can be directly detected in the secondaries' energy range O(1 EeV)-O(10 EeV) at the FD of Auger, when <math><mn>3</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>13</mn></mrow></msup><mo>≲</mo><msup><mrow><mi>ϵ</mi></mrow><mrow><mn>2</mn></mrow></msup><mo>≲</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>3</mn></mrow></msup></math>. And a new region of 0.7 GeV &lt; <math><msub><mrow><mi>m</mi></mrow><mrow><mi>M</mi><mi>C</mi><mi>P</mi></mrow></msub></math> &lt; 10 GeV and <math><mn>1.2</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>7</mn></mrow></msup></math> &lt; ϵ &lt; <math><mn>4.5</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>3</mn></mrow></msup></math> is ruled out in the <math><msub><mrow><mi>m</mi></mrow><mrow><mi>M</mi><mi>C</mi><mi>P</mi></mrow></msub></math>-ϵ plane with 14 years of Auger data.

China

Ye Xu

Jieqin Lan

Weiwei Gao

Measurement of upward-going milli-charged particles at the Pierre Auger Observatory

Dark matter particles could be superheavy, provided their lifetime is much longer than the age of the Universe. Using the sensitivity of the Pierre Auger Observatory to ultrahigh energy neutrinos and photons, we constrain a specific extension of the Standard Model of particle physics that meets the lifetime requirement for a superheavy particle by coupling it to a sector of ultralight sterile neutrinos. Our results show that, for a typical dark coupling constant of 0.1, the mixing angle <math><msub><mi>θ</mi><mi>m</mi></msub></math> between active and sterile neutrinos must satisfy, roughly, <math><msub><mi>θ</mi><mi>m</mi></msub><mo>≲</mo><mn>1.5</mn><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>6</mn></mrow></msup><mo>(</mo><msub><mi>M</mi><mi>X</mi></msub><mo>/</mo><msup><mn>10</mn><mn>9</mn></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi><msup><mo>)</mo><mrow><mo>−</mo><mn>2</mn></mrow></msup></math> for a mass <math><msub><mi>M</mi><mi>X</mi></msub></math> of the dark-matter particle between <math><msup><mn>10</mn><mn>8</mn></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math> and <math><msup><mn>10</mn><mn>11</mn></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>.

G. A. Anastasi

P. R. Araújo Ferreira

J. C. Arteaga Velázquez

Peru

J. A. Bellido

M. E. Bertaina

G. Bhatta

P. L. Biermann

P. G. Brichetto Orchera

F. L. Briechle

K. S. Caballero-Mora

J. A. Chinellato

R. W. Clay

A. C. Cobos Cerutti

M. R. Coluccia

P. J. Costa

C. E. Covault

C. S. Cruz Sanchez

B. R. Dawson

R. M. de Almeida

J. de Jesús

S. J. de Jong

J. R. T. de Mello Neto

I. De Mitri

J. de Oliveira

D. de Oliveira Franco

F. de Palma

V. de Souza

B. P. de Souza de Errico

E. De Vito

A. Del Popolo

A. di Matteo

Romania

M. Dobre

J. C. D’Olivo

Constraints on metastable superheavy dark matter coupled to sterile neutrinos with the Pierre Auger Observatory

Conventional scenarios of purely gravitationally produced dark matter with masses below the Hubble parameter at the end of inflation are in tension with cosmic microwave background (CMB) constraints on the isocurvature power spectrum. We explore a more general scenario with a nonminimal coupling between the scalar dark matter field and gravity, which allows for significantly lighter scalar dark matter masses compared to minimal coupling predictions. By imposing relic abundance, isocurvature, Lyman-<math><mi>α</mi></math>, and big bang nucleosynthesis (BBN) constraints, we show the viable parameter space for these models. Our findings demonstrate that the presence of a nonminimal coupling expands the parameter space, yielding a dark matter mass lower bound of <math><mn>2</mn><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>4</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>eV</mi></math>.

Marcos A. G. Garcia

Sarunas Verner

New window into gravitationally produced scalar dark matter

We investigate the production of a spectator scalar dark matter field that is directly coupled to the inflaton during inflation and reheating. We consider two specific inflationary potentials, namely the Starobinsky and T model of inflation, which satisfy the constraints on the scalar tilt, <math><mrow><msub><mrow><mi>n</mi></mrow><mrow><mi>s</mi></mrow></msub></mrow></math>, and tensor-to-scalar ratio, <math><mi>r</mi></math>, measured by the Planck satellite. Excitation of light scalar dark matter during inflation may result in large isocurvature perturbations, which can be avoided by inducing a sizable effective dark matter mass during the inflationary phase. For purely gravitational production, the Planck isocurvature constraints require the dark matter mass to be larger than the Hubble scale at horizon exit, with <math><msub><mi>m</mi><mi>χ</mi></msub><mo>≳</mo><mn>0.5</mn><msub><mi>H</mi><mo>*</mo></msub></math>. For small bare dark matter masses <math><msub><mi>m</mi><mi>χ</mi></msub><mo>≪</mo><msub><mi>H</mi><mo>*</mo></msub></math>, these constraints translate into a lower bound on the dark matter coupling to the inflaton. We argue that these constraints can be applied to a wide class of single-field slow-roll inflation models. We also derive isocurvature, dark matter abundance, and Lyman-<math><mi>α</mi></math> constraints on the direct coupling and bare dark matter mass.

Isocurvature constraints on scalar dark matter production from the inflaton

We investigate the out-of-equilibrium production of scalar dark matter (DM) from the inflaton condensate during inflation and reheating. We assume that this scalar couples only to the inflaton via a direct quartic coupling and is minimally coupled to gravity. We consider all possible production regimes: purely gravitational, weak direct coupling (perturbative), and strong direct coupling (nonperturbative). For each regime, we use different approaches to determine the dark matter phase space distribution and the corresponding relic abundance. For the purely gravitational regime, scalar dark matter quanta are copiously excited during inflation resulting in an infrared (IR) dominated distribution function and a relic abundance which overcloses the universe for a reheating temperature <math><msub><mi>T</mi><mi>reh</mi></msub><mo>&gt;</mo><mn>34</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>. A nonvanishing direct coupling induces an effective DM mass and suppresses the large IR modes in favor of ultraviolet (UV) modes and a minimal scalar abundance is generated when the interference between the direct and gravitational couplings is maximal. For large direct couplings, backreaction on the inflaton condensate is accounted for by using the Hartree approximation and lattice simulation techniques. Since scalar DM candidates can behave as noncold dark matter, we estimate the impact of such species on the matter power spectrum and derive the corresponding constraints from the Lyman-<math><mi>α</mi></math> measurements. We find that they correspond to a lower bound on the DM mass of <math><mo>≳</mo><mn>3</mn><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>4</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>eV</mi></math> for purely gravitational production, and <math><mo>≳</mo><mn>20</mn><mtext> </mtext><mtext> </mtext><mi>eV</mi></math> for direct coupling production. We discuss the implications of these results.

Scalar dark matter production from preheating and structure formation constraints

We investigate the impact of interactions between hidden sectors and the discovered Higgs boson  $$h_{125}$$  <math> <msub> <mi>h</mi> <mn>125</mn> </msub> </math>  , allowing for additional invisible decay channels of  $$h_{125}$$  <math> <msub> <mi>h</mi> <mn>125</mn> </msub> </math>  . We perform  $$\chi ^2$$  <math> <msup> <mi>χ</mi> <mn>2</mn> </msup> </math>  -fits to the measurements of the Higgs-boson cross sections as a function of the invisible branching ratio and different combinations of coupling modifiers, where the latter quantify modifications of the couplings of  $$h_{125}$$  <math> <msub> <mi>h</mi> <mn>125</mn> </msub> </math>   compared to the predictions of the Standard Model. We present generic results in terms of exclusion limits on the coupling modifiers and the invisible branching ratio of  $$h_{125}$$  <math> <msub> <mi>h</mi> <mn>125</mn> </msub> </math>  . Additionally, we apply our results to a variety of concrete model realizations containing a hidden sector: dark matter within Higgs- and singlet-portal scenarios, models featuring (pseudo) Nambu–Goldstone bosons and two Higgs doublet extensions. One of the main conclusions of our work is that in a wide class of models the indirect constraints resulting from the measurements of the cross sections of  $$h_{125}$$  <math> <msub> <mi>h</mi> <mn>125</mn> </msub> </math>   provide substantially stronger constraints on the invisible Higgs-boson branching ratio compared to the direct limits obtained from searches for the invisible decay of  $$h_{125}$$  <math> <msub> <mi>h</mi> <mn>125</mn> </msub> </math>  . However, we demonstrate that the presence of an invisible decay mode of  $$h_{125}$$  <math> <msub> <mi>h</mi> <mn>125</mn> </msub> </math>   can also open up parameter space regions which otherwise would be excluded as a result of the indirect constraints. As a byproduct of our analysis, we show that in light of the new results from the LZ collaboration a fermionic DM candidate within the simplest Higgs-portal scenario is ruled out under standard assumptions.

Thomas Biekötter

Higgs-boson visible and invisible constraints on hidden sectors

We present a measurement of the cosmic-ray spectrum above 100 PeV using the part of the surface detector of the Pierre Auger Observatory that has a spacing of 750 m. An inflection of the spectrum is observed, confirming the presence of the so-called second-knee feature. The spectrum is then combined with that of the 1500 m array to produce a single measurement of the flux, linking this spectral feature with the three additional breaks at the highest energies. The combined spectrum, with an energy scale set calorimetrically via fluorescence telescopes and using a single detector type, results in the most statistically and systematically precise measurement of spectral breaks yet obtained. These measurements are critical for furthering our understanding of the highest energy cosmic rays.

J. Albury

R. Alves Batista

H. Asorey

A. Badescu

A. Balaceanu

R. Barreira Luz

K. Becker

P. Billoir

A. Botti

T. Bretz

P. Buchholz

F. Canfora

I. Caracas

J. Carceller

A. Coleman

M. Coluccia

The energy spectrum of cosmic rays beyond the turn-down around  $$\varvec{10^{17}}$$  <math> <mrow> <msup> <mn>10</mn> <mn>17</mn> </msup> </mrow> </math>   eV as measured with the surface detector of the Pierre Auger Observatory