Belgium

Chiara Arina

France

Benjamin Fuks

Italy

Luca Panizzi

United States

Michael Baker

South Africa

Alan Cornell

Germany

Jan Heisig

United Kingdom

Benedikt Maier

Portugal

Rute Pedro

Dominique Trischuk

Diyar Agin

Alexandre Arbey

Giorgio Arcadi

Emanuele Bagnaschi

Kehang Bai

Brazil

Disha Bhatia

Mathias Becker

Alexander Belyaev

Ferdinand Benoit

Monika Blanke

Canada

Jackson Burzynski

Jonathan Butterworth

Antimo Cagnotta

China

Lorenzo Calibbi

Linda Carpenter

Spain

Xabier Cid Vidal

Emanuele Copello

Louie Corpe

Francesco D’Eramo

Aldo Deandrea

Australia

Aman Desai

Caterina Doglioni

South Korea

Sunil Dogra

Mathias Garny

Mark Goodsell

Norway

Sohaib Hassan

Philip Harris

Julia Harz

Alejandro Ibarra

Alberto Iorio

Felix Kahlhoefer

Deepak Kar

Egypt

Shaaban Khalil

Valery Khoze

Pyungwon Ko

Sabine Kraml

Greg Landsberg

Andre Lessa

Laura Lopez-Honorez

Alberto Mariotti

Vasiliki Mitsou

Kirtimaan Mohan

Chang-Seong Moon

Colombia

Alexander Moreno Briceno

Maria Moreno Llacer

Leandre Munoz-Aillaud

Taylor Murphy

Anele Ncube

Wandile Nzuza

Clarisse Prat

Lena Rathmann

Thobani Sangweni

Dipan Sengupta

William Shepherd

Sukanya Sinha

Tim Tait

Andrea Thamm

Michel Tytgat

Zirui Wang

David Yu

Shin-Shan Yu

Publisher Erratum: $\textit{t}$-channel dark matter models – a whitepaper

This report, summarising work achieved in the context of the LHC Dark Matter Working Group, investigates the phenomenology of $\textit{t}$-channel dark matter models, spanning minimal setups with a single dark matter candidate and mediator to more complex constructions closer to UV-complete models. For each considered class of models, we examine collider, cosmological and astrophysical implications. In addition, we explore scenarios with either promptly decaying or long-lived particles, as well as featuring diverse dark matter production mechanisms in the early universe. By providing a unified analysis framework, numerical tools and guidelines, this work aims to support future experimental and theoretical efforts in exploring $\textit{t}$-channel dark matter models at colliders and in cosmology.

$\textit{t}$-channel dark matter models – a whitepaper

We study the decay of a heavy CP-even neutral Higgs into an on-shell Standard Model-like Higgs boson and two photons, $\textit{H}$ → $\textit{hγγ}$, in the two-Higgs doublet model. We argue that the decay channel $\textit{H}$ → $\textit{hγγ}$, followed by the decay of the Standard Model Higgs $$ h\to b\overline{b} $$ , could be observed at the 5$\textit{σ}$ level at the High-Luminosity LHC for masses of the heavy Higgs up to 950 GeV for the type-II, 650 GeV for the Lepton Specific and the Flipped 2HDMs, and 350 GeV for the type-I. We also discuss the possible role of the decay $\textit{H}$ → $\textit{hγγ}$ in discriminating among different types of 2HDMs and in enhancing the total number of events in the final state $$ H\to b\overline{b}\gamma \gamma $$ compared to the cascade decay $\textit{H}$ → $\textit{hh}$ followed by $\textit{h}$ → $\textit{γγ h}$ → $$ b\overline{b} $$ with identical final state (although with different kinematical distributions).

Mexico

M. Arroyo-Ureña

Pablo Roig

T. Valencia-Pérez

Prospects for detecting the rare heavy Higgs decay $\textit{H}$ → $\textit{hγγ}$ through the $$ H\to b\overline{b}\gamma \gamma $$ channel at the LHC

We calculate the renormalization group equation (RGE) of the lepton-number-violating Weinberg operator with the particle content of the Standard Model (SM), thus completing the set of two-loop RGEs of the SM effective field theory up to dimension 5. We identify new diagrams that could increase the rank of the Wilson coefficient of the Weinberg operator, and we calculate the complete two-loop RGE for the neutrino mass eigenvalues and leptonic mixing matrix. We also briefly discuss some phenomenological implications of the RGEs.

Nicholas Leister

Di Zhang

Complete two-loop renormalization group equation of the Weinberg operator

In some scenarios, the dark matter relic abundance is set by the semi-annihilation of two dark matter particles into one dark matter particle and one Standard Model particle. These semi-annihilations might still be occurring today in the galactic center at a significant rate, generating a flux of boosted dark matter particles. We investigate the possible signals of this flux component in direct detection and neutrino experiments for sub-GeV dark matter masses. We show that for typical values of the semi-annihilation cross-section, the sensitivity of current experiments to the spin-independent dark matter-proton scattering cross-section can be several orders of magnitude larger than current constraints from cosmic-ray boosted dark matter. We also argue that the upcoming DARWIN and DUNE experiments may probe scattering cross-sections as low as <math altimg='si1.svg'><msup><mrow><mn>10</mn></mrow><mrow><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo><mn>37</mn></mrow></msup><mspace width='0.2em' /><msup><mrow><mi mathvariant='normal'>cm</mi></mrow><mrow><mn>2</mn></mrow></msup></math> for masses between 30 MeV and 1 GeV.

Boris Betancourt Kamenetskaia

Japan

Motoko Fujiwara

Takashi Toma

Boosted dark matter from semi-annihilations in the galactic center

The Casas-Ibarra (CI) parametrization of the Yukawa coupling matrix of Majorana neutrinos is generalized by considering the exact seesaw relation and including non-unitarity of the <math><mn>3</mn><mo>×</mo><mn>3</mn></math> Pontecorvo-Maki-Nakagawa-Sakata (PMNS) flavor mixing matrix. With the help of a full <math><mn>6</mn><mo>×</mo><mn>6</mn></math> Euler-like block description of the flavor structure for the seesaw mechanism, we find that the orthogonal matrix <math><mi>O</mi></math> in the CI parametrization can be expressed as <math><msub><mrow><mi>O</mi></mrow><mrow><mi>i</mi><mi>j</mi></mrow></msub><mo>=</mo><msqrt><mrow><msub><mrow><mi>M</mi></mrow><mrow><mi>j</mi></mrow></msub><mo>/</mo><msub><mrow><mi>m</mi></mrow><mrow><mi>i</mi></mrow></msub></mrow></msqrt><mspace width="0.05cm"></mspace><msub><mrow><mi>F</mi></mrow><mrow><mi>i</mi><mi>j</mi></mrow></msub></math> with <math><msub><mrow><mi>m</mi></mrow><mrow><mi>i</mi></mrow></msub></math> and <math><msub><mrow><mi>M</mi></mrow><mrow><mi>j</mi></mrow></msub></math> being the masses of light and heavy Majorana neutrinos and <math><msub><mrow><mi>F</mi></mrow><mrow><mi>i</mi><mi>j</mi></mrow></msub></math> consisting of the PMNS and active-sterile flavor mixing parameters (for <math><mi>i</mi><mo>,</mo><mi>j</mi><mo>=</mo><mn>1</mn><mo>,</mo><mn>2</mn><mo>,</mo><mn>3</mn></math>). Assuming a specific pattern of <math><mi>O</mi></math> is therefore equivalent to imposing some special conditions on the seesaw parameter space.

Zhi-zhong Xing

On the orthogonal matrix in the Casas-Ibarra parametrization for the Yukawa interactions of Majorana neutrinos

We consider electrically neutral complex-vector particles <math><mi>V</mi></math> below the GeV mass scale that, from a low-energy perspective, couple to the photon via higher-dimensional form factor interactions. We derive ensuing astrophysical constraints by considering the anomalous energy loss from the Sun, Horizontal Branch, and Red Giant stars as well as from SN1987A that arise from vector pair production in these environments. Under the assumption that the dark states <math><mi>V</mi></math> constitute dark matter, the bounds are then complemented by direct and indirect detection as well as cosmological limits. The relic density from freeze-out and freeze-in mechanisms is also computed. On the basis of a UV-complete model that realizes the considered effective couplings, we also discuss the naturalness of the constrained parameter space, and provide an analysis of the zero mass limit of <math><mi>V</mi></math>.

Austria

Xiaoyong Chu

Junji Hisano

Jui-Lin Kuo

CERN

Josef Pradler

Multipole vector dark matter below the GeV scale

Using a new sample of extremely metal poor systems, the EMPRESS survey has recently reported a primordial helium abundance that is <math><mn>3</mn><mi>σ</mi></math> smaller than the prediction from the standard big bang nucleosynthesis (BBN) scenario. This measurement could be interpreted as a hint for a primordial lepton asymmetry in the electron neutrino flavor. Motivated by the EMPRESS results, we present a comprehensive analysis of the lepton asymmetry using measurements of the abundances of primordial elements, along with cosmic microwave background (CMB) data from Planck. Assuming that there is no dark radiation in our Universe, we find an electron neutrino chemical potential <math><mrow><msub><mrow><mi>ξ</mi></mrow><mrow><msub><mrow><mi>ν</mi></mrow><mrow><mi>e</mi></mrow></msub></mrow></msub><mo>=</mo><mn>0.043</mn><mo>±</mo><mn>0.015</mn></mrow></math>, which deviates from zero by <math><mn>2.9</mn><mi>σ</mi></math>. If no assumption is made on the abundance of dark radiation in the Universe, the chemical potential is <math><mrow><msub><mrow><mi>ξ</mi></mrow><mrow><msub><mrow><mi>ν</mi></mrow><mrow><mi>e</mi></mrow></msub></mrow></msub><mo>=</mo><mn>0.046</mn><mo>±</mo><mn>0.021</mn></mrow></math>, which deviates from zero by <math><mn>2.2</mn><mi>σ</mi></math>. We also find that this result is rather insensitive to the choice of nuclear reaction rates. If the true helium abundance corresponds to the EMPRESS central value, future CMB observations from the Simons Observatory and CMB-S4 will increase the significance for a nonzero lepton asymmetry to <math><mn>4</mn><mi>σ</mi></math> and <math><mn>5</mn><mi>σ</mi></math> respectively, assuming no dark radiation, or to <math><mn>3</mn><mi>σ</mi></math> when no assumption is made on the abundance of dark radiation.

Miguel Escudero

Victor Maura

Primordial lepton asymmetries in the precision cosmology era: Current status and future sensitivities from BBN and the CMB

We perform an effective field theory analysis to correlate the charged lepton flavor violating processes <math><msub><mo>ℓ</mo><mi>i</mi></msub><mo>→</mo><msub><mo>ℓ</mo><mi>j</mi></msub><mi>γ</mi><mi>γ</mi></math> and <math><msub><mo>ℓ</mo><mi>i</mi></msub><mo>→</mo><msub><mo>ℓ</mo><mi>j</mi></msub><mi>γ</mi></math>. Using the current upper bounds on the rate for <math><msub><mo>ℓ</mo><mi>i</mi></msub><mo>→</mo><msub><mo>ℓ</mo><mi>j</mi></msub><mi>γ</mi></math>, we derive model-independent upper limits on the rates for <math><msub><mo>ℓ</mo><mi>i</mi></msub><mo>→</mo><msub><mo>ℓ</mo><mi>j</mi></msub><mi>γ</mi><mi>γ</mi></math>. Our indirect limits are about three orders of magnitude stronger than the direct bounds from current searches for <math><mi>μ</mi><mo>→</mo><mi>e</mi><mi>γ</mi><mi>γ</mi></math>, and four orders of magnitude better than current bounds for <math><mi>τ</mi><mo>→</mo><mo>ℓ</mo><mi>γ</mi><mi>γ</mi></math>. We also stress the relevance of Belle II or a Super Tau Charm Facility to discover the rare decay <math><mi>τ</mi><mo>→</mo><mo>ℓ</mo><mi>γ</mi><mi>γ</mi></math>.

Fabiola Fortuna

Xabier Marcano

Marcela Marín

Indirect upper limits on <math><msub><mo>ℓ</mo><mi>i</mi></msub><mo>→</mo><msub><mo>ℓ</mo><mi>j</mi></msub><mi>γ</mi><mi>γ</mi></math> from <math><msub><mo>ℓ</mo><mi>i</mi></msub><mo>→</mo><msub><mo>ℓ</mo><mi>j</mi></msub><mi>γ</mi></math>

For Majorana fermions the anapole moment is the only allowed electromagnetic multipole moment. In this work we calculate the anapole moment induced at one-loop by the Yukawa and gauge interactions of a Majorana fermion, using the pinch technique to ensure the finiteness and gauge-invariance of the result. As archetypical example of a Majorana fermion, we calculate the anapole moment for the lightest neutralino in the Minimal Supersymmetric Standard Model, and specifically in the bino, wino and higgsino limits. Finally, we briefly discuss the implications of the anapole moment for the direct detection of dark matter in the form of Majorana fermions.

Merlin Reichard

Ryo Nagai

Anapole moment of Majorana fermions and implications for direct detection of neutralino dark matter