We present a new study on the Gravity-Mediated Dark Matter (GMDM) scenario, where interactions between dark matter (DM) and the Standard Model are mediated by spin-two particles. Expanding on this established framework, we explore a novel regime characterized by a low reheating temperature that offers an alternative to the conventional thermal relic paradigm. This approach opens new possibilities for understanding the dynamics of the dark sector, encompassing both the dark matter particles (fermion, scalar and vector) and the spin-two mediators. Our analysis examines the constraints imposed by the relic abundance of DM, collider experiments, and direct detection searches, spanning a wide mass range for the dark sector, from very light to extremely heavy states. This work opens new possibilities for the phenomenology of GMDM.

South Korea

Hyun Lee

Myeonghun Park

Spain

Veronica Sanz

Gravity-Mediated Dark Matter at a low reheating temperature

We consider D-branes in the Dabholkar-Park (DP) background, a 9d orientifold theory obtained by gauging symmetry in the type IIB string theory compactified on a circle. Using anomalies in the world-sheet theory, we provide physical insights into the classification of stable D-branes by relative KR-theory. The nature, such as stability, of D-branes wrapping along the compactified circle can be extracted from information about 1d Majorana fermions on the boundary of the world-sheet. These Majorana fermions need to be introduced to consistently perform the GSO projection and the orientifold. We also construct D-brane states in the DP background. The spectrum of D-branes characterized by the relative KR-theory is correctly reproduced from the D-brane states.

Japan

Hiroki Wada

Satoshi Yamaguchi

Anomalies and D-branes in the Dabholkar-Park background

In collider experiments, an event is characterized by two distinct yet mutually complementary features: the “global features” and the “local features.” Kinematic information such as the event topology of a hard process, masses, and spins of particles comprises global features spanning the entire phase space. This global feature can be inferred from reconstructed objects. In contrast, representations of particles in gauge groups, such as quantum chromodynamics (QCD), offer localized features revealing the dynamics of an underlying theory. These local features, particularly observed in the patterns of radiation as raw data in various detector components, complement the global kinematic features. We propose a simple but effective neural network architecture that seamlessly integrates information from both kinematics and QCD to enhance the signal sensitivity at colliders.

Kayoung Ban

United States

Kyoungchul Kong

Seong Chan Park

Exploring the synergy of kinematics and dynamics for collider physics

The Standard Model (SM) Higgs boson, the most recently discovered elementary particle, may still serve as a mediator between the SM sector and a new physics sector related to dark matter (DM). The Large Hadron Collider (LHC) has not yet fully constrained the physics associated with the Higgs boson, leaving room for such possibilities. Among the various potential mass scales of the dark sector, the sub-GeV mass range is particularly intriguing. This parameter space presents significant challenges for DM direct detection experiments that rely on nuclear recoils. Various innovative experimental methods are currently under investigation to explore this sub-GeV dark sector. The LHC, functioning as a Higgs factory, could explore this sector once the challenge of identifying DM signals is resolved. Due to the significantly lower mass of particles in the dark sector compared to the Higgs boson, these particles are expected to be highly boosted following the Higgs boson’s decay. However, detecting and identifying these highly boosted particles remains a considerable challenge at the LHC, despite their eventual decay into SM particles. We employ a well-motivated leptophobic   <math> <msubsup> <mi>Z</mi> <mi>B</mi> <mo>′</mo> </msubsup> </math>  $$ {Z}_B^{\prime } $$  model as a prototype to analyze the distinctive signatures from Higgs boson exotic decays into multi-photons. These signatures consist of collimated photons that fail to meet the photon isolation criteria, forming jet-like objects. Conventional analyses relying solely on the purity of energy deposits in the electromagnetic calorimeter would fail to detect these signatures, as they would be overwhelmed by background events from Quantum Chromodynamics. To effectively distinguish between such novel signal signatures and SM background events, we leverage advanced machine learning techniques, specifically the transformer encoder in a multimodal network structure. This neural network successfully separates dark sector signals from SM backgrounds, outperforming traditional event selection analyses.

A. Hammad

P. Ko

China

Chih-Ting Lu

Exploring exotic decays of the Higgs boson to multi-photons at the LHC via multimodal learning approaches

The choice of optimal event variables is crucial for achieving the maximal sensitivity of experimental analyses. Over time, physicists have derived suitable kinematic variables for many typical event topologies in collider physics. Here, we introduce a deep-learning technique to design good event variables, which are sensitive over a wide range of values for the unknown model parameters. We demonstrate that the neural networks trained with our technique on some simple event topologies are able to reproduce standard event variables like invariant mass, transverse mass, and stransverse mass. The method is automatable and completely general and can be used to derive sensitive, previously unknown, event variables for other, more complex event topologies.

Doojin Kim

Konstantin T. Matchev

Prasanth Shyamsundar

Deep-learned event variables for collider phenomenology

Freeze-in mechanism provides robust dark matter production in the early Universe. Because of its feeble interactions, freeze-in dark matter leaves signals at colliders which are often involved with long-lived particle decays and consequent displaced vertices (DV). In this paper, we develop a method to read off mass spectrum of particles being involved in the DV events at the LHC. We demonstrate that our method neatly works under limited statistics, detector resolution, and smearing effects. The signature of DV at the LHC can come from either highly suppressed phase space or a feeble coupling of particle decay processes. By measuring invisible particle mass spectrum, one can discriminate these two cases and thus extract information of dominant freeze-in processes in the early Universe at the LHC.

Kyu Jung Bae

Mengchao Zhang

Demystifying freeze-in dark matter at the LHC

We examine the discovery potential for double Higgs production at the high luminosity LHC in the final state with two b-tagged jets, two leptons and missing transverse momentum. Although this dilepton final state has been considered a difficult channel due to the large backgrounds, we argue that it is possible to obtain sizable signal significance, by adopting a deep learning framework making full use of the relevant kinematics along with the jet images from the Higgs decay. For the relevant number of signal events we obtain a substantial increase in signal sensitivity over existing analyses. We discuss relative improvements at each stage and the correlations among the different input variables for the neutral network. The proposed method can be easily generalized to the semi-leptonic channel of double Higgs production, as well as to other processes with similar final states.

Jeong Kim

Minho Kim

Konstantin Matchev

Portraying double Higgs at the Large Hadron Collider

The phenomenology of the dark sector is complicated if the dark sector is charged under a confined hidden gauge group. In such a kind of model, a dark parton produced at a high-energy collider showers and hadronizes to a cluster of dark mesons. Dark mesons then decay to visible particles and produce a jetlike signal, which is called a “dark jet” in this work. Collider signal of a dark jet depend on the property of dark mesons. For example, a finite lifetime of a dark meson would provide a displaced vertex or displaced track; thus, one can use these displaced objects to tag a dark jet. However, if the lifetime of a dark meson is collider negligible (too short to manifest a displaced vertex), it would be difficult to distinguish a dark jet from standard model QCD jets. In this work, we propose a new tagging strategy to identify dark jets from QCD backgrounds. This strategy is based on jet-substructure analysis. We study various jet-substructure variables and find out variables with good discrimination ability. Our result shows that by combining multiple jet-substructure variables one could distinguish dark jets from QCD background and thus enhance the sensitivity of the dark sector search at a collider.

Tagging a jet from a dark sector with jet substructures at colliders

Many standard model extensions, including composite Goldstone Higgs models, predict vector-like fermionic top-partners at the TeV scale. The intensive search programmes by ATLAS and CMS focus on decays into a 3$^{rd}$ generation quark and an electroweak boson (<math><mi>W</mi><mo>,</mo><mi>Z</mi><mo>,</mo><mi>h</mi></math>). However, underlying models of partial compositeness contain additional states that give rise to exotic top partner decays. We consider a well-motivated scenario in which a charge-2/3 top-partner decays into a pseudo-scalar, <math><mi>T</mi><mo>→</mo><mi>t</mi><mspace width="0.25em"></mspace><mi>a</mi></math>, with <math><mi>a</mi><mo>→</mo><mi>g</mi><mi>g</mi><mtext> or </mtext><mi>b</mi><mover><mrow><mi>b</mi></mrow><mrow><mo>¯</mo></mrow></mover></math> dominating below the <math><mi>t</mi><mover><mrow><mi>t</mi></mrow><mrow><mo>¯</mo></mrow></mover></math> threshold. We show that the constraints on the top partner mass from QCD pair production are substantially weakened, still allowing a top partner mass as light as 400 GeV.

France

Giacomo Cacciapaglia

Thomas Flacke

Exotic decays of top partners: Mind the search gap

Off-shell Higgs bosons at the high mass tail may shed light on the underlying mechanism of the electroweak symmetry breaking. In the Standard Model, there is an exact cancellation of the logarithmic divergence between the box and Higgs-mediated triangle diagrams due to unitarity, such that the <math><mi>g</mi><mi>g</mi><mo>→</mo><mi>Z</mi><mi>Z</mi><mo>(</mo><mi>W</mi><mi>W</mi><mo>)</mo></math> process is left with a negligible <math><msub><mi>V</mi><mi>L</mi></msub><msub><mi>V</mi><mi>L</mi></msub></math> longitudinal mode contribution in the tail region of the off-shell Higgs boson. We propose to test the unitarity of the Standard Model by probing this behavior, as new physics violating this cancellation at certain tail region can be probed by a precision study of the <math><msub><mi>V</mi><mi>L</mi></msub><msub><mi>V</mi><mi>L</mi></msub></math> mode. To this end, we propose to utilize the information in angular observables to maximize the sensitivity of the <math><msub><mi>V</mi><mi>L</mi></msub><msub><mi>V</mi><mi>L</mi></msub></math> final states in the high mass tail region.

Seung J. Lee

Zhuoni Qian

Probing unitarity violation in the tail of the off-shell Higgs boson in <math><msub><mi>V</mi><mi>L</mi></msub><msub><mi>V</mi><mi>L</mi></msub></math> mode