We propose a minimal scenario for light thermal dark matter (DM) in sub-GeV to GeV range by incorporating a scalar singlet DM in a type-I seesaw scenario extended by an additional Higgs doublet $\textit{ϕ}$ . The latter permits efficient annihilation of light scalar DM into leptonic final states including right-handed neutrinos (RHN). We keep the charged fermion as well as neutral fermion final states in forbidden regime to avoid bounds from indirect search as well as cosmic microwave background (CMB) data. After studying the purely forbidden DM scenario with neutral and charged fermion final states separately, we discuss the interplay of forbidden and non-forbidden channels in generating light thermal DM relic by considering neutral fermions in non-forbidden mode due to relatively weaker constraints. The model can also explain the anomalous magnetic moment of muon, W-mass anomaly and saturate experimental bounds on charged lepton flavour violation and DM direct detection while offering tantalising detection prospects of RHN, the mass of which is kept approximately in the same range as DM.

India

Debasish Borah

Pritam Das

South Korea

Satyabrata Mahapatra

Narendra Sahu

Light thermal dark matter via type-I seesaw portal

We propose a minimal type-I Dirac seesaw which accommodates a thermal scalar dark matter (DM) candidate protected by a charge conjugation symmetry in dark sector <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>C</mi><mrow><mi>dark</mi></mrow></msub></math>, without introducing any additional field beyond the ones taking part in the seesaw. A <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>Z</mi><mn>4</mn></msub></math> symmetry is introduced to realize the tree level Dirac seesaw while the Majorana mass terms are prevented by an unbroken global lepton number symmetry. While the spontaneous <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>Z</mi><mn>4</mn></msub></math> breaking together with electroweak symmetry breaking lead to the generation of light Dirac neutrino mass, it also results in the formation of domain walls. These cosmologically catastrophic walls can be made to annihilate away by introducing bias terms while also generating stochastic gravitational waves within reach of near future experiments like LISA, BBO, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>μ</mi></math>-ARES, etc. The scalar DM parameter space can be probed at direct and indirect search experiments. Light Dirac neutrinos also enhance the 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 experiments. The model can also explain the observed baryon asymmetry via Dirac leptogenesis.

Zafri Ahmed Borboruah

United States

Lekhika Malhotra

Utkarsh Patel

Minimal Dirac seesaw dark matter

We study the possibility of the highest energy neutrino event with 220 PeV energy, detected recently by the KM3NeT experiment to be originating from heavy dark matter (DM) decay. Considering a heavy right handed neutrino (RHN) DM for illustrative purposes, we show that DM mass of 440 PeV, can explain the observed flux. The required DM lifetime to produce the best-fit value of the neutrino flux saturates the existing gamma-ray bounds. Due to the large uncertainty in the flux, it is possible to explain the KM3NeT event from RHN DM decay at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>3</mn><mi>σ</mi></math> confidence level (CL) while being in agreement with gamma-ray bounds and nonobservation of similar events at IceCube. While we consider a gauged <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>B</mi><mo>−</mo><mi>L</mi></math> scenario where DM relic can be generated due to other interactions, we also briefly discuss some alternate DM possibilities where the gamma-ray bounds can be alleviated compared to the minimal RHN DM discussed here.

Nayan Das

Nobuchika Okada

China

Prantik Sarmah

Possible origin of the KM3-230213A neutrino event from dark matter decay

We propose a novel leptogenesis scenario utilising the two-body decay of heavy right handed neutrino (RHN) via the electromagnetic dipole operator. While the requirement of the standard model (SM) gauge invariance requires such dipole operator only at dimension-6 forcing the generation of non-zero CP asymmetry from three-body decay with two-loop corrections, we write down dimension-5 dipole operators involving heavy RHN <math altimg='si1.svg'><msub><mrow><mi>N</mi></mrow><mrow><mi>R</mi></mrow></msub></math> and its lighter counterpart <math altimg='si2.svg'><msub><mrow><mi>&#957;</mi></mrow><mrow><mi>R</mi></mrow></msub></math>. This allows the generation of lepton asymmetry in <math altimg='si2.svg'><msub><mrow><mi>&#957;</mi></mrow><mrow><mi>R</mi></mrow></msub></math> from two-body decay of heavy RHN 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 to baryon asymmetry via electroweak sphalerons. The lepton number violation by heavy RHN also induces a one-loop Majorana mass of <math altimg='si2.svg'><msub><mrow><mi>&#957;</mi></mrow><mrow><mi>R</mi></mrow></msub></math> rendering the light neutrinos to be Majorana fermions. While smallness of the Majorana mass of <math altimg='si2.svg'><msub><mrow><mi>&#957;</mi></mrow><mrow><mi>R</mi></mrow></msub></math> prevents additional sources or washout of lepton asymmetry, it also constrains the scale of leptogenesis. Sub-GeV sterile neutrinos, depending upon their masses come with interesting implications for low energy experiments, neutrino oscillation, warm dark matter as well as effective relativistic degrees of freedom. Additionally, heavy RHN can lead to observable monochromatic photon signatures at terrestrial experiments.

Arnab Dasgupta

Electromagnetic leptogenesis with light-heavy sterile neutrinos

Amaterasu, the second most energetic (244 EeV) cosmic ray particle has been recently detected by the Telescope Array (TA) surface detector. The origin of the TA Amaterasu event is puzzling, as its arrival direction points back to a void in the local Universe, lacking conventional astrophysical ultrahigh-energy (UHE) cosmic ray sources. Hence, we explore the possibility if this TA Amaterasu event could have originated from the decay of superheavy dark matter (SHDM) in the Milky Way. Such an origin also opens up multimessenger detection channels in both UHE gamma rays and UHE neutrinos. In this present work, using the TA Amaterasu event and the multimessenger limits/sensitivities from various UHE telescopes, we place stringent constraints on the lifetime and mass of the SHDM. We find that the nondetection of the corresponding gamma rays at the Pierre Auger Observatory (PAO) and the TA is in severe tension with the SHDM parameter space required to explain the TA Amaterasu event. Additionally, we extend the multimessenger analysis to the future UHE gamma-ray and UHE neutrino telescopes such as PAO upgrade, GRAND 200k, and IceCube-Gen2. We find that the bounds from the future neutrino telescopes will be able to compete with the present UHECR bounds. However, compared to the existing UHE gamma-ray bounds, the future PAO upgrade and the GRAND 200k gamma-ray detectors will improve the bounds on SHDM lifetime by at least one order of magnitude.

Sovan Chakraborty

Poonam Mehta

Constraining the superheavy dark matter origin of ultrahigh-energy cosmic rays with the Amaterasu event

We study the generation of baryon asymmetry as well as dark matter (DM) in an extended reheating period after the end of slow-roll inflation. Within the regime of perturbative reheating, we consider different monomial potential of the inflaton field during reheating era. The inflaton condensate reheats the Universe by decaying into the Standard Model (SM) bath either via fermionic or bosonic decay modes. Assuming the leptogenesis route to baryogenesis in a canonical seesaw framework with three right handed neutrinos (RHN), we consider both the radiation bath and perturbative inflaton decay to produce such RHNs during the period of reheating when the maximum temperature of the SM bath is well above the reheating temperature. The DM, assumed to be a SM gauge singlet field, also gets produced from the bath during the reheating period via UV freeze-in. In addition to obtaining different parameter space for such nonthermal leptogenesis and DM for both bosonic and fermionic reheating modes and the type of monomial potential, we discuss the possibility of probing such scenarios via spectral shape of primordial gravitational waves.

Basabendu Barman

Arindam Basu

Amit Chakraborty

United Kingdom

Rishav Roshan

Testing leptogenesis and dark matter production during reheating with primordial gravitational waves

We propose a new realization of light Dirac neutrino mass and dark matter (DM) within the framework of a non-Abelian discrete flavor symmetry based on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>A</mi><mn>4</mn></msub></math> group. In addition to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>A</mi><mn>4</mn></msub></math>, we also consider a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>Z</mi><mn>2</mn></msub></math> and an unbroken global lepton number symmetry <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><mi>L</mi></msub></math> to keep unwanted terms away while guaranteeing the Dirac nature of light neutrinos. The field content, their transformations, and flavon vacuum alignments are chosen in such a way that the type-I Dirac seesaw generates only one light Dirac neutrino mass while the other two masses arise from scotogenic contributions at one-loop. This leads to the Dirac scoto-seesaw framework, a generalization of the widely studied scoto-seesaw model to Dirac neutrinos. The symmetry breaking of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>A</mi><mn>4</mn></msub></math> leaves a remnant <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi mathvariant="script">Z</mi><mn>2</mn></msub></math> symmetry responsible for stabilizing DM. Dirac nature of light neutrinos introduces additional relativistic degrees of freedom <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">Δ</mi><msub><mi>N</mi><mi>eff</mi></msub></math> within reach of cosmic microwave background experiments.

Poland

Biswajit Karmakar

Discrete dark matter with light Dirac neutrinos

We study the discovery prospects of leptophilic dark matter (DM) in future lepton colliders by considering the light neutrinos to be of Dirac type. Adopting an effective field theory (EFT) approach, we write down dimension six operators connecting the standard model (SM) fields, light Dirac neutrinos and DM. Considering DM relic to be generated via the thermal freeze-out, we check the discovery prospects at future lepton colliders via mono-photon plus missing energy searches. The right chiral parts of light Dirac neutrinos get thermalised due to their interactions with the bath as well as leptophilic DM, leading to enhanced effective relativistic degrees of freedom within reach of future cosmic microwave background (CMB) experiments. The interplay of existing bounds from cosmological observations related to DM relic and , direct and indirect detection of DM, astrophysics, and collider observations leave promising discovery prospects at future electron and muon colliders along with complementary signatures at future CMB experiments.

Sahabub Jahedi

Bhavya Thacker

Collider and CMB complementarity of leptophilic dark matter with light Dirac neutrinos

With entropy injection, an early matter-dominated epoch (EMD) impels the axion decay constant <math><msub><mi>f</mi><mi>a</mi></msub></math> toward larger values to produce correct axion dark matter (DM) abundance, thereby unfolding the low-mass axion (<math><mrow><msub><mrow><mi>m</mi></mrow><mrow><mi>a</mi></mrow></msub><mo>≲</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>5</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>eV</mi></mrow></math>) parameter space to be searched for in axion experiments. We implement this proposition in a scenario where <math><msub><mi>f</mi><mi>a</mi></msub></math> and the leptogenesis scale in a seesaw mechanism are equivalent. We show that if, instead, the EMD is provided by evaporating ultralight primordial black holes (PBHs), the scenario becomes strikingly testable with gravitational wave (GW) background alongside the axion searches. In particular, while being consistent with correct axion DM abundance, the scale <math><mrow><msub><mrow><mi>f</mi></mrow><mrow><mi>a</mi></mrow></msub><mo>≳</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>12</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math>, corresponding to the unflavored regime of leptogenesis with hierarchical right-handed neutrinos, can be probed with GW and axion experiments, which is otherwise not testable at neutrino or collider experiments. Additionally, axions produced from PBH evaporation can give rise to dark radiation within reach of future cosmic microwave background experiments.

Suruj Jyoti Das

Czechia

Italy

Rome Samanta

Cogenesis of baryon and dark matter with PBHs and the QCD axion

We study the possibility of testing a dark matter (DM) scenario embedded in a global lepton number symmetry <math><mi>U</mi><mo>(</mo><mn>1</mn><msub><mo>)</mo><mi>L</mi></msub></math> via gravitational waves (GWs) and cosmic microwave background (CMB) observations. The spontaneous breaking of <math><mi>U</mi><mo>(</mo><mn>1</mn><msub><mo>)</mo><mi>L</mi></msub></math> symmetry generates the seesaw scale as well as DM mass dynamically. The (pseudo-)Nambu-Goldstone boson, known as a Majoron, acquires nonzero mass due to soft symmetry-breaking terms of quadratic type in the scalar potential, which eventually breaks <math><mi>U</mi><mo>(</mo><mn>1</mn><msub><mo>)</mo><mi>L</mi></msub></math> to its <math><msub><mi>Z</mi><mn>2</mn></msub></math> subgroup. The spontaneous symmetry breaking, which effectively breaks <math><msub><mi>Z</mi><mn>2</mn></msub></math>, leads to the formation of domain walls (DWs), posing a threat to successful cosmology, if allowed to dominate. As gravity does not respect any global symmetries, we consider higher-dimensional operators suppressed by the scale of quantum gravity (QG), namely, <math><msub><mi>Λ</mi><mrow><mi>QG</mi></mrow></msub></math>, which introduces the required bias leading to DW annihilation and emission of stochastic GWs observable at near future experiments. The same operators also lead to decay of DM bringing interesting indirect detection aspects. While DM is produced nonthermally via scalar portal interactions, light Majorons can give rise to additional <math><mi>Δ</mi><msub><mi>N</mi><mi>eff</mi></msub></math> within reach of future CMB experiments.

Observable gravitational waves and <math><mrow><mi>Δ</mi><msub><mrow><mi>N</mi></mrow><mrow><mi>eff</mi></mrow></msub></mrow></math> with global lepton number symmetry and dark matter