We present a minimal composite dark matter model, based on a SU($\textit{N}$ ) dark sector with $\textit{n}$ dark quarks and a heavy t-channel mediator. For $\textit{n}$ ≥ 4, the dark flavor symmetry guarantees the stability of a subset of the dark pions, which serve as our dark matter candidates. Their relic abundance is determined by dark sector annihilation with the remaining dark pions, which are unstable and decay. Due to their degenerate masses, the annihilation cross section is suppressed at low temperatures, thereby avoiding stringent constraints from indirect detection and opening up the GeV mass window. The decaying dark pions are naturally long lived. We obtain limits on the model from semi-visible or emerging jet searches and estimate the reach of future probes.

Spain

Adrián Carmona

Germany

Fatemeh Elahi

United States

Christiane Scherb

Pedro Schwaller

Dark showers from sneaky dark matter

In this paper we explore the possibility of utilizing Deep Learning in measuring the CP properties of the coupling of Higgs boson to $\textit{τ}$ leptons at the High Luminosity Large Hadron Collider. We employ three Deep Learning (DL) networks, Multi-Layer Perceptron (MLP), Graph Convolution Network (GCN), and Graph Transformer Network (GTN) to enhance signal-to-background separation. The angle between $\textit{τ}$ lepton decay planes at the detector level is CP-sensitive observables, and we develop Heterogeneous Graphs that integrate diverse node and edge structures to incorporate the CP-sensitive observable efficiently. Using simplified detector simulations we estimate the reconstruction accuracy of the angle between $\textit{τ}$ lepton planes at the detector level, considering hadronic $\textit{τ}$ decay modes and standard model backgrounds. With $$ \sqrt{s} $$ = 14 TeV and $$ \mathcal{L} $$ = 100 fb , MLP excludes CP mixing angles above 20° at 68% confidence level (CL), while GCN and GTN achieve exclusions at 90% CL and 95% CL, respectively. The networks also achieve a 3$\textit{σ}$ significance in excluding a pure CP-odd state.

W. Esmail

Japan

A. Hammad

M. Nojiri

Testing CP properties of the Higgs boson coupling to $\textit{τ}$ leptons with heterogeneous graphs

We study thermal production of dark matter (DM) in a realization of the minimal models of Bonnefoy et al. [Phys. Rev. Lett. 131, 221802 (2023)], where parity is used to solve the strong <math><mi>C</mi><mi>P</mi></math> problem by transforming the entire Standard Model (SM) into a mirror copy. Although the mirror electron <math><msup><mi>e</mi><mo>′</mo></msup></math> is a good DM candidate, its viability is mired by the presence of the mirror up quark <math><msup><mi>u</mi><mo>′</mo></msup></math>, whose abundance is intimately related to the <math><msup><mi>e</mi><mo>′</mo></msup></math> abundance and must be suppressed. This can be achieved through a sequential freeze-in mechanism, where mirror photons are first produced from SM gluons, and then the mirror photons produce <math><msup><mi>e</mi><mo>′</mo></msup></math>. After computing the details of this double freeze-in, we discuss the allowed parameter space of the model, which lies at the threshold of experimental observations. We find that this origin of <math><msup><mi>e</mi><mo>′</mo></msup></math> DM requires a low reheating temperature after inflation and is consistent with the baryon asymmetry arising from leptogenesis, providing mirror neutrinos have a significant degeneracy. Finally, we show that this <math><msup><mi>e</mi><mo>′</mo></msup></math> DM is not compatible with Higgs parity, the simplest scheme with exact parity, unless SM parameters deviate significantly from their central values or the minimal model is extended.

Quentin Bonnefoy

Lawrence Hall

Claudio Andrea Manzari

Amara McCune

Dark matter in a mirror solution to the strong <math><mi>C</mi><mi>P</mi></math> problem

We propose theories of a complete mirror world with parity (<math><mi>P</mi></math>) solving the strong <math><mi>C</mi><mi>P</mi></math> problem. <math><mrow><mi>P</mi></mrow></math> exchanges the entire standard model with its mirror copy. We derive bounds on the two new mass scales that arise: <math><msup><mi>v</mi><mo>′</mo></msup></math> where parity and mirror electroweak symmetry are spontaneously broken, and <math><msub><mi>v</mi><mn>3</mn></msub></math> where the color groups break to the diagonal strong interactions. The strong <math><mi>C</mi><mi>P</mi></math> problem is solved even if <math><mrow><msub><mrow><mi>v</mi></mrow><mrow><mn>3</mn></mrow></msub><mo>≪</mo><msup><mrow><mi>v</mi></mrow><mrow><mo>′</mo></mrow></msup></mrow></math>, when heavy colored states at the scale <math><msub><mi>v</mi><mn>3</mn></msub></math> may be accessible at LHC and future colliders. Furthermore, we argue that the breaking of <math><mi>P</mi></math> introduces negligible contributions to <math><msub><mover><mi>θ</mi><mo>¯</mo></mover><mi>QCD</mi></msub></math>, starting at three-loop order. The symmetry breaking at <math><msub><mi>v</mi><mn>3</mn></msub></math> can be made dynamical, without introducing an additional hierarchy problem.

Colorful Mirror Solution to the Strong <math><mi>C</mi><mi>P</mi></math> Problem

We investigate the consequences of models where dark sector quarks could be produced at the LHC, which subsequently undergo a dark parton shower, generating jets of dark hadrons that ultimately decay back to Standard Model hadrons. This yields collider objects that can be nearly indistinguishable from Standard Model jets, motivating the reliance on substructure observables to tease out the signal. However, substructure predictions are sensitive to the details of the incalculable dark hadronization. We show that the Lund jet plane provides a very effective tool for designing observables that are resilient against the unknown impact of dark hadronization on the substructure properties of dark sector jets.

CERN

Switzerland

Timothy Cohen

Jennifer Roloff

Dark sector showers in the Lund jet plane

In this work, we consider the case of a strongly coupled dark/hidden sector, which extends the Standard Model (SM) by adding an additional non-Abelian gauge group. These extensions generally contain matter fields, much like the SM quarks, and gauge fields similar to the SM gluons. We focus on the exploration of such sectors where the dark particles are produced at the LHC through a portal and undergo rapid hadronization within the dark sector before decaying back, at least in part and potentially with sizeable lifetimes, to SM particles, giving a range of possibly spectacular signatures such as emerging or semi-visible jets. Other, non-QCD-like scenarios leading to soft unclustered energy patterns or glueballs are also discussed. After a review of the theory, existing benchmarks and constraints, this work addresses how to build consistent benchmarks from the underlying physical parameters and present new developments for the pythia Hidden Valley module, along with jet substructure studies. Finally, a series of improved search strategies is presented in order to pave the way for a better exploration of the dark showers at the LHC.

France

Guillaume Albouy

Canada

Jared Barron

Taiwan

Hugues Beauchesne

Elias Bernreuther

United Kingdom

Marcella Bona

Cesare Cazzaniga

Cari Cesarotti

Annapaola Cosa

David Curtin

Zeynep Demiragli

Sweden

Caterina Doglioni

Alison Elliot

Karri DiPetrillo

Florian Eble

Carlos Erice

Chad Freer

Aran Garcia-Bellido

Caleb Gemmell

Marie-Hélène Genest

Italy

Giovanni Cortona

Giuliano Gustavino

Nicoline Hemme

Tova Holmes

South Africa

Deepak Kar

Simon Knapen

Austria

Suchita Kulkarni

Luca Lavezzo

Belgium

Steven Lowette

Benedikt Maier

Seán Mee

Stephen Mrenna

India

Harikrishnan Nair

Jeremi Niedziela

Christos Papageorgakis

Nukulsinh Parmar

Christoph Paus

Kevin Pedro

Ana Peixoto

Alexx Perloff

Tilman Plehn

Jessie Shelton

Akanksha Singh

Sukanya Sinha

Torbjörn Sjöstrand

Aris Spourdalakis

Daniel Stolarski

Matthew Strassler

Netherlands

Andrii Usachov

Carlos Sierra

Christopher Verhaaren

Long Wang

Theory, phenomenology, and experimental avenues for dark showers: a Snowmass 2021 report

Extended scalar sectors with additional degrees of freedom appear in many scenarios beyond the Standard Model. Heavy scalar resonances that interact with the neutral current could be discovered via broad resonances in the tails of the four-lepton invariant mass spectrum, where the Standard Model background is small and well understood. In this article we consider a recent ATLAS measurement of four-lepton final states, where the data is in excess over the background for invariant masses above 500 GeV. We discuss the possibility that this excess could be interpreted as a “double peak” from the two extra heavy neutral scalars of a CP violating Two Higgs Doublet Model, both coupling to the Z boson. We apply an iterative fitting procedure to find viable model parameters that can match the excess, resulting in a benchmark point where the observed four-lepton invariant mass spectrum can be explained by two scalar particles H 2 and H 3, with masses of 544 GeV and 629 GeV, respectively, being admixtures of the CP eigenstates. Our explanation predicts additional production processes for   <math> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> </math>  $$ t\overline{t} $$ , W + W  − , 4b and γγ, some of which have cross sections close to the current experimental limits. Our results further imply that the electric dipole moment of the electron should be close to the present bounds.

Stefan Antusch

Oliver Fischer

South Korea

Egypt

Explaining excesses in four-leptons at the LHC with a double peak from a CP violating Two Higgs Doublet Model

We propose a search for long lived axion-like particles (ALPs) in exotic top decays. Flavour-violating ALPs appear as low energy effective theories for various new physics scenarios such as t-channel dark sectors or Froggatt-Nielsen models. In this case the top quark may decay to an ALP and an up- or charm-quark. For masses in the few GeV range, the ALP is long lived across most of the viable parameter space, suggesting a dedicated search. We propose to search for these long lived ALPs in   <math> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> </math>  $$ t\overline{t} $$  events, using one top quark as a trigger. We focus on ALPs decaying in the hadronic calorimeter, and show that the ratio of energy deposits in the electromagnetic and hadronic calorimeters as well as track vetoes can efficiently suppress Standard Model backgrounds. Our proposed search can probe exotic top branching ratios smaller than 10 −4 with a conservative strategy at the upcoming LHC run, and potentially below the 10 −7 level with more advanced methods. Finally we also show that measurements of single top production probe these branching ratios in the very short and very long lifetime limit at the 10 −3 level.

Adrian Carmona

The ALPs from the top: searching for long lived axion-like particles from exotic top decays

Axion-like particles (ALPs) are ubiquitous in models of new physics explaining some of the most pressing puzzles of the Standard Model. However, until relatively recently, little attention has been paid to its interplay with flavour. In this work, we study in detail the phenomenology of ALPs that exclusively interact with up-type quarks at the tree-level, which arise in some well-motivated ultra-violet completions such as QCD-like dark sectors or Froggatt-Nielsen type models of flavour. Our study is performed in the low-energy effective theory to highlight the key features of these scenarios in a model independent way. We derive all the existing constraints on these models and demonstrate how upcoming experiments at fixed-target facilities and the LHC can probe regions of the parameter space which are currently not excluded by cosmological and astrophysical bounds. We also emphasize how a future measurement of the currently unavailable meson decay D → π + invisible could complement these upcoming searches.

Charming ALPs

We explore the constraints current collider searches place on a QCD-like dark sector. A combination of multi-jet, multi-jet plus missing energy and emerging jets searches is used to derive constraints on the mediator mass across the full range of the dark meson lifetimes for the first time.

Hanna Mies

Collider constraints on dark mediators