Certain models of inert multiplets allow for semi-annihilation processes, in which two dark matter candidates annihilate to a dark matter particle and a non-dark matter particle. The existence of these processes can alleviate certain constraints and substantially modify the indirect detection signal. In this paper, we study current indirect detection constraints on the semi-annihilation of inert scalar multiplets. We show that there exist gauge numbers for which dark matter can be thermally produced and be compatible with indirect detection constraints even for very cuspy galactic dark matter density profiles.

Taiwan

Hugues Beauchesne

Cheng-Wei Chiang

Indirect detection constraints on semi-annihilation of inert scalar multiplets

Many new physics models include secluded sectors that interact little with the Standard Model and whose internal interactions control the dark matter abundance. If these same interactions are responsible for maintaining kinematic equilibrium within the secluded sector, it is possible that the phase-space distributions will differ considerably from their thermal values during freeze-out. This can potentially result in deviations of the dark matter abundance from that computed under the assumption of thermal distributions. In this paper, we revisit dark matter abundance computations for a benchmark secluded sector by numerically tracking the phase-space distributions. Namely, we show that the dark matter abundance can deviate considerably from standard results during the freeze-out process, but that a longer period of annihilation ultimately leaves only a slight excess.

Impact of non-thermal phase-space distributions on dark matter abundance in secluded sectors

Dark matter semi-annihilation is a process through which two dark matter candidates annihilate to a single dark matter particle and a non-dark matter particle. Such processes are common when the symmetry stabilizing the dark matter differs from ℤ2 and can lead to qualitatively different phenomenology. In this work, we study the viability of semi-annihilation models including one or two inert multiplets. For one multiplet, we show that there does not exist any viable model in which semi-annihilation is efficient. For two multiplets, semi-annihilation can be efficient, but the number of viable and technically natural models is limited. We then perform a detailed study of the most promising model, showing that the correct relic abundance can be obtained for a wide range of masses.

Dark matter semi-annihilation for inert scalar multiplets

Weak supervision searches have in principle the advantages of both being able to train on experimental data and being able to learn distinctive signal properties. However, the practical applicability of such searches is limited by the fact that successfully training a neural network via weak supervision can require a large amount of signal. In this work, we seek to create neural networks that can learn from less experimental signal by using transfer and meta-learning. The general idea is to first train a neural network on simulations, thereby learning concepts that can be reused or becoming a more efficient learner. The neural network would then be trained on experimental data and should require less signal because of its previous training. We find that transfer and meta-learning can substantially improve the performance of weak supervision searches.

Zong-En Chen

Improving the performance of weak supervision searches using transfer and meta-learning

New physics could manifest itself in the form of electroweak multiplets that interact at tree level with the Higgs boson but do not mix with Standard Model fields or acquire expectation values. In this paper, we study the potential contributions of such inert multiplets to several crucial Higgs properties, namely, the branching ratio of the Higgs to a Z boson and a photon (or massless dark photon) and the triple Higgs coupling. Constraints from the Higgs signal strengths, oblique parameters and unitarity are taken into account.

Contributions of inert electroweak multiplets to Higgs properties

Many collider searches have attempted to detect the Higgs boson decaying to a photon and an invisible massless dark photon. For the branching ratio to this channel to be realistically observable at the LHC, there must exist new mediators that interact with both the standard model and the dark photon. In this paper, we study experimental and theoretical constraints on an extensive set of mediator models. We show that these constraints limit the Higgs branching ratio to a photon and a dark photon to be far smaller than the current sensitivity of collider searches.

Observability of the Higgs boson decay to a photon and a dark photon

This Letter proposes a new signature for confining dark sectors at the Large Hadron Collider. Under the assumption of a QCD-like hidden sector, hadronic jets containing stable dark bound states could manifest in proton-proton collisions. We present a simplified model with a  $$Z'$$  <math> <msup> <mi>Z</mi> <mo>′</mo> </msup> </math>   boson yielding the production of jets made up of dark bound states and subsequently leading to the decays of those that are unstable to  $$\tau $$  <math> <mi>τ</mi> </math>   leptons and Standard Model quarks. The resulting signature is characterised by non-isolated  $$\tau $$  <math> <mi>τ</mi> </math>   lepton pairs inside semi-visible jets. We estimate the constraints on our model from existing CMS and ATLAS analyses. We propose a set of variables that leverage the leptonic content of the jet and exploit them in a supervised jet tagger to enhance the signal-to-background separation. Furthermore, we discuss the performance and limitations of current triggers for accessing sub-TeV  $$Z'$$  <math> <msup> <mi>Z</mi> <mo>′</mo> </msup> </math>   masses, as well as possible strategies that can be adopted by experiments to access such low mass regions. We estimate that with the currently available triggers, a high mass search can claim a  $$5 \sigma $$  <math> <mrow> <mn>5</mn> <mi>σ</mi> </mrow> </math>   discovery (exclusion) of the  $$Z'$$  <math> <msup> <mi>Z</mi> <mo>′</mo> </msup> </math>   boson with a mass up to 4.5 TeV (5.5 TeV) with the full Run 2 data of the LHC when the fraction of unstable dark hadrons decaying to  $$\tau $$  <math> <mi>τ</mi> </math>   lepton pairs is around  $$50\%$$  <math> <mrow> <mn>50</mn> <mo>%</mo> </mrow> </math>  , and with a coupling of the  $$Z'$$  <math> <msup> <mi>Z</mi> <mo>′</mo> </msup> </math>   to right-handed up-type quarks of 0.25. Furthermore, we show that, with new trigger strategies for Run 3, it may be possible to access  $$Z'$$  <math> <msup> <mi>Z</mi> <mo>′</mo> </msup> </math>   masses down to 700 GeV, for which the event topology is still composed of two resolved semi-visible jets.

Switzerland

Cesare Cazzaniga

Annapaola Cosa

United Kingdom

Caterina Doglioni

Tobias Fitschen

Italy

Giovanni Cortona

China

Ziyuan Zhou

Uncovering tau leptons-enriched semi-visible jets at the LHC

Many attempts have been made to observe the decay of the Higgs boson to a photon and an invisible massless dark photon. For this decay to be potentially observable at the LHC, new mediators that communicate between the standard model and the dark photon must exist. In this Letter, we study bounds on such mediators coming from the Higgs signal strengths, oblique parameters, electric dipole moment of the electron, and unitarity. We find that the branching ratio of the Higgs boson to a photon and a dark photon is constrained to be far smaller than the sensitivity of current collider searches, thus calling for a reconsideration of current experimental efforts.

Is the Decay of the Higgs Boson to a Photon and a Dark Photon Currently Observable at the LHC?

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

Germany

Guillaume Albouy

Canada

Jared Barron

United States

Elias Bernreuther

Marcella Bona

Cari Cesarotti

Timothy Cohen

David Curtin

Zeynep Demiragli

Sweden

Alison Elliot

Karri DiPetrillo

Florian Eble

Carlos Erice

Chad Freer

Aran Garcia-Bellido

Caleb Gemmell

Marie-Hélène Genest

CERN

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

Christiane Scherb

Pedro Schwaller

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

Considerable efforts have been dedicated to discovering a dark photon via the decay of the Higgs boson to a photon and an invisible particle. A subject that is still mostly unexplored is which properties of the dark photon could be measured at the LHC if an excess were to be found in this channel and whether we could determine if this signal is indeed that of a dark photon. In this paper, we seek to address some of these questions for two Higgs production channels: gluon-fusion and Z-associated. First, prospects are presented for the upper limit on the mass of a massless dark photon and for the uncertainty on the mass of a massive dark photon. Second, we study the feasibility of distinguishing this signal from that of the Higgs decaying to a gravitino and a neutralino that decays to a photon and another gravitino. Finally, the complementary possibility of observing the decay of the Higgs to a dark photon and a Z boson is studied.

Measuring properties of a dark photon from semi-invisible decay of the Higgs boson