We propose a novel collider probe of baryogenesis at TeV scale by measuring decay asymmetries into particle and anti-particle final states. Motivated by the idea of Dirac leptogenesis, we consider an extension of the standard model with new colored and SU(2) singlet particles in such a way that the out-of-equilibrium decay of heavy colored fermions creates equal and opposite CP asymmetries in two sectors, prevented from equilibrating with each other. While the TeV scale viability of this mechanism requires a resonantly enhanced CP asymmetry, the latter also plays a crucial role leading to observable decay asymmetries in colliders. In addition to discussing conventional signatures of such heavy colored particles, namely, mono-jet plus missing transverse energy, displaced vertex, colored track at hadron colliders, we also show the unique possibility of measuring decay asymmetries via forward-backward and charge asymmetries at future muon colliders. In addition to being a verifiable TeV-scale baryogenesis scenario, the model also predicts a singlet scalar dark matter candidate consistent with the required thermal dark matter properties near the Higgs resonance.

India

Debasish Borah

United States

Kun Cheng

Arnab Dasgupta

Tao Han

Keping Xie

Collider probes of baryogenesis with maximal CP asymmetry

The persistent null results at dark matter (DM) direct-detection experiments have pushed the popular weakly interacting massive particle (WIMP) DM to tight corners. Generic WIMP models with direct-detection rates below the current upper limits often lead to a thermally overproduced relic abundance after freeze-out. To resolve this conundrum, we propose a novel scenario where DM has temperature-dependent couplings with the standard model (SM) bath. A scalar field having a large vacuum expectation value (VEV) at high temperatures generates sizeable DM-SM interactions, leading to efficient DM annihilations responsible for generating the desired thermal relic. At lower temperatures, the scalar field VEV settles down to a small value as a result of a phase transition which can generically be of first order, effectively leading to a suppressed DM-SM interaction rate at low temperature, consistent with null results at direct-detection experiments. The upper bound on thermal DM mass forces the first-order phase transition to occur at scales such that the corresponding gravitational wave signal remains within reach of future experiments such as the Laser Interferometer Space Antenna.

Tong Arthur Wu

Reviving WIMP dark matter with temperature-dependent couplings

Spontaneous breaking of discrete symmetries like <italic>Z</italic> <inf>2</inf> leads to the formation of stable topological defects such as domain walls which, if allowed to dominate, can potentially be in conflict with cosmological observations. Incorporating explicit <italic>Z</italic> <inf>2</inf>-breaking bias terms can lead to annihilation of such walls while also emitting stochastic gravitational waves (GW). We study the role of heavy right-handed neutrinos present in the type-I seesaw framework to generate such a bias term via quantum corrections. This offers interesting correlations among the seesaw scale, GW peak amplitude and peak frequency which can be probed at present and future experiments related to GW as well as precision measurements of the cosmic microwave background (CMB). In flavor symmetric UV complete scenarios with degenerate RHNs at leading order, such tiny coupling of RHNs to a <italic>Z</italic> <inf>2</inf>-odd scalar can also lead to small mass splittings suitable for explaining the observed baryon asymmetry of the universe via resonant leptogenesis.

Indrajit Saha

Gravitational waves from seesaw assisted collapsing domain walls

Gravitational effects are known to violate global symmetries, threatening the Peccei-Quinn solution to the strong <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math> problem. Ultraviolet completions featuring a gauged <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>U</mi><mo stretchy="false">(</mo><mn>1</mn><mo stretchy="false">)</mo></math> symmetry, where <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>U</mi><mo stretchy="false">(</mo><mn>1</mn><msub><mo stretchy="false">)</mo><mrow><mi>PQ</mi></mrow></msub></math> arises as an accidental global symmetry, can suppress Planck-suppressed operators, enabling high-quality axions in a mass window where it can also account for the observed dark matter (DM) in the Universe. We show that in such models, the spontaneous breaking of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>U</mi><mo stretchy="false">(</mo><mn>1</mn><mo stretchy="false">)</mo></math> gauge symmetry generates a strong stochastic gravitational wave background (SGWB) from gauge cosmic string loops. Even in the most conservative scenario, for breaking scales <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo>≳</mo><msup><mn>10</mn><mn>14</mn></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>, the SGWB signal strength can exceed astrophysical foregrounds across a broad frequency range. Such quality axion models have a characteristic IR break frequency originating from the dynamics of the string-wall network collapse. We propose this characteristic SGWB frequency-amplitude region, identified as signature-window-axion-gravitational waves (SWAG), to be a novel probe of high-quality axion DM at future space and ground-based interferometers.

Disha Bandyopadhyay

Nayan Das

Italy

Rome Samanta

High-quality axion dark matter at gravitational wave interferometers

We propose a novel and minimal setup where the observed baryon asymmetry of the Universe and neutrino oscillation data can be satisfied with only one right-handed neutrino and a second Higgs doublet with the latter being also responsible for driving cosmic inflation. While inflation is realized via nonminimal coupling of the Higgs to gravity, baryon asymmetry is generated via Affleck-Dine leptogenesis. Due to the presence of only two new fields beyond the standard model (BSM), the proposed setup remains very predictive with only a small allowed parameter space consistent with the PLANCK 2018 and ACT 2025 data simultaneously. The preferred mass spectrum of the BSM particles also keeps the detection prospects alive at terrestrial experiments.

South Korea

Suruj Jyoti Das

Nobuchika Okada

Leptogenesis and neutrino mass with one right-handed neutrino and Higgs inflaton

We study the viability of light thermal dark matter (DM) in the sub-GeV mass range in view of the stringent new DAMIC-M limits on DM-electron scattering. Considering a Dirac fermion singlet DM charged under a new Abelian gauge symmetry <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>U</mi><mo stretchy="false">(</mo><mn>1</mn><mo stretchy="false">)</mo></math>, we outline two possibilities: (i) family nonuniversal <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>U</mi><mo stretchy="false">(</mo><mn>1</mn><mo stretchy="false">)</mo></math> gauge coupling with resonantly enhanced DM annihilation into Standard Model (SM) fermions, and (ii) family universal dark <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>U</mi><mo stretchy="false">(</mo><mn>1</mn><mo stretchy="false">)</mo></math> gauge symmetry where relic density is set by DM annihilation into light gauge bosons. As an illustrative example of the first class of models, we consider a gauged <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>L</mi><mi>μ</mi></msub><mo>−</mo><msub><mi>L</mi><mi>τ</mi></msub></math> extension of the SM having interesting detection prospects at several experiments. While both of these classes of models lead to the observed DM relic and consistency with DAMIC-M together with other experimental limits, the second class of models also lead to strong DM self-interactions, potentially solving the small-scale structure issues of cold dark matter. While a vast part of the parameter space in both the models is already ruled out, the current allowed region of parameter space can be further probed at ongoing or future experiments, keeping the models testable.

Satyabrata Mahapatra

Narendra Sahu

Vicky Singh Thounaojam

Light thermal dark matter models in the light of DAMIC-M 2025 constraints

Dark matter (DM), in spite of being stable or long-lived on cosmological scales, can decay in the early Universe due to finite-temperature effects. In particular, a first order phase transition (FOPT) in the early Universe can provide a finite window for such decay, guaranteeing DM stability at lower temperatures, consistent with observations. The FOPT can lead to the generation of stochastic gravitational waves (GW) with peak frequencies correlated with DM mass. On the other hand, early DM decay into neutrinos can create a large neutrino asymmetry which can have interesting cosmological consequences in terms of enhanced effective relativistic degrees of freedom <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>N</mi></mrow><mrow><mi>eff</mi></mrow></msub></mrow></math>, providing a solution to the recently observed helium anomaly among others. Allowing DM decay to occur below sphaleron decoupling temperature, thereby avoiding overproduction of baryon asymmetry, forces the FOPT to occur at subelectroweak scale. This leaves the stochastic GW within range of experiments like LISA, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>μ</mi><mi>ARES</mi></math>, NANOGrav etc.

Large neutrino asymmetry from forbidden decay of dark matter

We propose a novel cogenesis scenario by utilizing the two-body decay of heavy right-handed neutrinos (RHNs) via an effective operator involving an axionlike particle (ALP), dark matter (DM), and a light chiral fermion <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ν</mi><mi>R</mi></msub></math>. This allows the two-body decay of heavy RHNs into <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ν</mi><mi>R</mi></msub></math> and ALP, thereby generating a lepton asymmetry in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ν</mi><mi>R</mi></msub></math> which later gets transferred to left-handed leptons via sizeable Yukawa coupling with a neutrinophilic Higgs doublet. The asymmetry in left-handed leptons is then converted into baryon asymmetry via electroweak sphalerons. The lepton number violation by heavy RHNs also induces a one-loop Majorana mass of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ν</mi><mi>R</mi></msub></math> rendering the light neutrinos to be Majorana fermions. Successful leptogenesis constrains the parameter space in terms of RHN mass and axion decay constant. This has interesting consequences for both ALP and QCD axion DM parameter space within reach of several ongoing and near future experiments. We also propose a Dirac version of this scenario without any total lepton number violation. This leads to a long-lived asymmetric Dirac fermion contributing partially to DM, thereby opening up more parameter space for ALP. In addition to axion search experiments, the proposed scenarios can have observable signatures at cosmic microwave background and DM search as well as terrestrial particle physics experiments.

Cogenesis with ALPs

We propose a multi-messenger frontier probe of non-thermal or freeze-in massive particle (FIMP) dark matter (DM) by considering an effective field theory (EFT) setup. Assuming leptophilic operators connecting DM with the standard model (SM) bath, we consider DM mass ($\textit{m}$ ) and the reheat temperature of the Universe ($\textit{T}$ ) in a regime which prevents DM-SM thermalisation. Low $\textit{T}$ allows sizeable DM-SM interactions even for non-thermal DM allowing the latter to be probed at direct, indirect detection frontiers as well as future electron-positron and muon colliders. An extended reheating period governed by monomial inflaton potential after its slow-roll phase not only generates the required abundance of non-thermal DM via ultraviolet (UV) freeze-in but also brings the scale-invariant primordial gravitational waves (GW) within reach of near future experiments across a wide range of frequencies. While particle physics experiments can probe $\textit{T}$ ∼ 𝒪(10) GeV and FIMP DM with mass $\textit{m}$ ~ 𝒪(1) TeV, future GW detectors are sensitive to a much wider parameter space.

China

Sahabub Jahedi

Dipankar Pradhan

Multi-messenger FIMP

We study the possibility of light Dirac neutrino portal dark matter (DM) in an effective field theory setup. Dirac nature of light neutrino automatically includes its right chiral part <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ν</mi><mi>R</mi></msub></math> which, in our setup, also acts like a portal between DM and the standard model (SM) particles. Considering a Dirac fermion singlet DM stabilized by an unbroken <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>Z</mi><mn>2</mn></msub></math> symmetry, we write down all possible dimension-6 effective operators involving DM-<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ν</mi><mi>R</mi></msub></math> as well as <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ν</mi><mi>R</mi></msub></math>-SM which conserve <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>Z</mi><mn>2</mn></msub></math>, global lepton number and SM gauge symmetries. DM thermalization also ensures the thermalization of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ν</mi><mi>R</mi></msub></math>, leading to enhanced effective relativistic degrees of freedom <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>N</mi><mi>eff</mi></msub></math>, within reach of future cosmic microwave background (CMB) experiments. We study the complementarity among DM and CMB related observations for different Lorentz structures of effective operators. We also propose a UV complete gauged B-L symmetric model with Dirac neutrino portal dark matter.

Japan

Dibyendu Nanda

Sujit Kumar Sahoo

Effective theory of light Dirac neutrino portal dark matter with observable <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">Δ</mi><msub><mi>N</mi><mrow><mi>eff</mi></mrow></msub></math>