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.

India

United States

Debasish Borah

Nayan Das

China

Sahabub Jahedi

Dipankar Pradhan

Multi-messenger FIMP

<p>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.</p>

Nobuchika Okada

Prantik Sarmah

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

<p>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.</p>

Sovan Chakraborty

Poonam Mehta

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

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.

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.

South Korea

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.

United Kingdom

Rishav Roshan

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

We propose a gauged <math><mi>U</mi><mo>(</mo><mn>1</mn><msub><mo>)</mo><mrow><mi>B</mi><mo>−</mo><mi>L</mi></mrow></msub></math> version of the light Dirac neutrino portal dark matter. The <math><mi>U</mi><mo>(</mo><mn>1</mn><msub><mo>)</mo><mrow><mi>B</mi><mo>−</mo><mi>L</mi></mrow></msub></math> symmetry provides a UV completion by naturally accommodating three right-handed neutrinos from anomaly cancellation requirements which, in combination with the left-handed neutrinos, form the sub-eV Dirac neutrinos after electroweak symmetry breaking. The particle content and the gauge charges are chosen in such a way that light neutrinos remain purely Dirac and dark matter, a gauge singlet Dirac fermion, remain stable. We consider both thermal and nonthermal production possibilities of dark matter and correlate the corresponding parameter space with the one within reach of future cosmic microwave background (CMB) experiments sensitive to enhanced relativistic degrees of freedom <math><mi>Δ</mi><msub><mi>N</mi><mi>eff</mi></msub></math>. The interplay of dark matter, CMB, structure formation and other terrestrial constraints keep the scenario very predictive leading the <math><mi>U</mi><mo>(</mo><mn>1</mn><msub><mo>)</mo><mrow><mi>B</mi><mo>−</mo><mi>L</mi></mrow></msub></math> parameter space into tight corners.

Light Dirac neutrino portal dark matter with gauged <math><mi>U</mi><mo>(</mo><mn>1</mn><msub><mo>)</mo><mrow><mi>B</mi><mo>−</mo><mi>L</mi></mrow></msub></math> symmetry

We study the possibility of detecting dark radiation (DR) produced by a combination of interactions with the thermal bath and ultralight primordial black hole (PBH) evaporation in the early Universe. We show that the detection prospects via cosmic microwave background (CMB) measurements of the effective relativistic degrees of freedom <math><mrow><mi>Δ</mi><msub><mi>N</mi><mrow><mi>eff</mi></mrow></msub></mrow></math> get enhanced in some part of the parameter space compared to the purely nonthermal case where DR is produced solely from a PBH. On the other hand, for a certain part of the parameter space, DR that initially decouples from the bath, followed by its production from PBH evaporation, can reenter the thermal bath leading to much tighter constraints on the PBH parameter space. We also discuss the complementary detection prospects via observation of stochastic gravitational waves (GW) sourced by PBH density perturbations. The complementary probes offered by CMB and GW observations keep the detection prospects of such light degrees of freedom very promising in spite of limited discovery prospects at particle physics experiments.

Thermalized dark radiation in the presence of a PBH: <math><mrow><mi>Δ</mi><msub><mi>N</mi><mrow><mi>eff</mi></mrow></msub></mrow></math> and gravitational waves complementarity

We propose a scenario where dark matter (DM) can be generated nonthermally due to the presence of a light Dirac neutrino portal between the standard model (SM) and dark sector particles. The SM is minimally extended by three right-handed neutrinos (<math><msub><mi>ν</mi><mi>R</mi></msub></math>), a Dirac fermion DM candidate (<math><mi>ψ</mi></math>) and a complex scalar (<math><mi>ϕ</mi></math>), transforming nontrivially under an unbroken <math><msub><mi>Z</mi><mn>4</mn></msub></math> symmetry while being singlets under the SM gauge group. While DM and <math><msub><mi>ν</mi><mi>R</mi></msub></math> couplings are considered to be tiny in order to be in the nonthermal or freeze-in regime, <math><mi>ϕ</mi></math> can be produced either thermally or nonthermally depending upon the strength of its Higgs portal coupling. We consider both these possibilities and find out the resulting DM abundance via freeze-in mechanism to constrain the model parameters in the light of Planck 2018 data. Since the interactions producing DM also produce relativistic <math><msub><mi>ν</mi><mi>R</mi></msub></math>, we check the enhanced contribution to the effective relativistic degrees of freedom <math><mi>Δ</mi><msub><mi>N</mi><mi>eff</mi></msub></math> in view of existing bounds as well as future sensitivities. We also check the stringent constraints on free-streaming length of such freeze-in DM from structure formation requirements. Such constraints can rule out DM mass all the way up to <math><mi>O</mi><mo>(</mo><mn>100</mn><mtext> </mtext><mtext> </mtext><mi>keV</mi><mo>)</mo></math> keeping the <math><mi>Δ</mi><msub><mi>N</mi><mi>eff</mi></msub><mo>≤</mo><mi>O</mi><mo>(</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>3</mn></mrow></msup><mo>)</mo></math> out of reach from near future experiments. Possible extensions of this minimal model can lead to observable <math><mi>Δ</mi><msub><mi>N</mi><mi>eff</mi></msub></math> which can be probed at next generation experiments.

Anirban Biswas

Dibyendu Nanda

Freeze-in dark matter via a light Dirac neutrino portal

Precise measurements of  $$b\rightarrow c\tau \bar{\nu }$$  <math> <mrow> <mi>b</mi> <mo>→</mo> <mi>c</mi> <mi>τ</mi> <mover> <mrow> <mi>ν</mi> </mrow> <mrow> <mo>¯</mo> </mrow> </mover> </mrow> </math>   decays require large resource-intensive Monte Carlo (MC) samples, which incorporate detailed simulations of detector responses and physics backgrounds. Extracted parameters may be highly sensitive to the underlying theoretical models used in the MC generation. Because new physics (NP) can alter decay distributions and acceptances, the standard practice of fitting NP Wilson coefficients to SM-based measurements of the  $$R(D^{(*)})$$  <math> <mrow> <mi>R</mi> <mo>(</mo> <msup> <mi>D</mi> <mrow> <mo>(</mo> <mrow></mrow> <mo>∗</mo> <mo>)</mo> </mrow> </msup> <mo>)</mo> </mrow> </math>   ratios can be biased. The newly developed Hammer software tool enables efficient reweighting of MC samples to arbitrary NP scenarios or to any hadronic matrix elements. We demonstrate how Hammer allows avoidance of biases through self-consistent fits directly to the NP Wilson coefficients. We also present example analyses that demonstrate the sizeable biases that can otherwise occur from naive NP interpretations of SM-based measurements. The Hammer library is presently interfaced with several existing experimental analysis frameworks and we provide an overview of its structure.