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

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.

Disha Bandyopadhyay

Cogenesis with ALPs

The left-right model with the simplest Higgs structure has a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>S</mi><mi>U</mi><mo stretchy="false">(</mo><mn>2</mn><msub><mrow><mo stretchy="false">)</mo></mrow><mrow><mi>L</mi></mrow></msub></mrow></math> doublet <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>H</mi><mi>L</mi></msub></math>, a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi><mi>U</mi><mo stretchy="false">(</mo><mn>2</mn><msub><mo stretchy="false">)</mo><mi>R</mi></msub></math> doublet <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>H</mi><mi>R</mi></msub></math>, and a singlet <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>σ</mi></math> that couples to the doublets as <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>σ</mi><mo stretchy="false">(</mo><mo stretchy="false">|</mo><msub><mi>H</mi><mi>L</mi></msub><msup><mo stretchy="false">|</mo><mn>2</mn></msup><mo>−</mo><mo stretchy="false">|</mo><msub><mi>H</mi><mi>R</mi></msub><msup><mo stretchy="false">|</mo><mn>2</mn></msup><mo stretchy="false">)</mo></math>. The left-right symmetry has <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>H</mi><mi>L</mi></msub><mo stretchy="false">↔</mo><msub><mi>H</mi><mi>R</mi></msub></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>σ</mi><mo stretchy="false">↔</mo><mo>−</mo><mi>σ</mi></math>. We study gravitational wave production and baryogenesis in the electroweak phase transitions in the model. For two benchmark points, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>σ</mi></math> first gets a vev, followed by <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>H</mi><mi>R</mi></msub></math> and then <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>H</mi><mi>L</mi></msub></math>. An interesting feature is that the vev of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>H</mi><mi>L</mi></msub></math> is initially much higher than its zero temperature value, leading to a more strongly first-order transition and higher frequency gravitational waves. An unusual benchmark point has the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>σ</mi></math> vev at zero when the electroweak symmetry breaks. This results in both <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>H</mi><mi>L</mi></msub></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>H</mi><mi>R</mi></msub></math> vevs being equal and in the multi-TeV range. At a lower temperature, the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>σ</mi></math> vev turns on, breaking the left-right symmetry and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>H</mi><mi>L</mi></msub></math> drops to its standard model value. Since the electroweak symmetry is broken at the multi-TeV scale, the frequency of gravitational waves will be much higher than usual. Baryogenesis is also discussed.

Matthew Knauss

Marc Sher

Gravitational wave production and baryogenesis in a simple left-right model

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.

Electromagnetic leptogenesis with light-heavy sterile neutrinos

We study the possibility of constraining a scenario with high scale first order phase transition (FOPT) responsible for the cogenesis of baryon and dark matter using gravitational wave (GW) (non)observations. While the FOPT at high scale is responsible for generating baryon asymmetry through leptogenesis and dark matter via the mass-gain mechanism, the resulting GW spectrum falls within the ongoing LIGO-Virgo experimental sensitivity. The dark matter is preferred to be in the nonthermal ballpark with sub-GeV masses and the criteria of successful dark matter relic rules out a large portion of the parameter space consistent with high scale FOPT and successful leptogenesis. Some part of the parameter space allowed from dark matter and leptogenesis criteria also gives rise to a large signal-to-noise ratio at ongoing experiments and hence can be disfavored in a conservative way from the nonobservation of such stochastic GW background. Future data from ongoing and planned experiments will offer a complementary and indirect probe of the remaining parameter space which is typically outside the reach of any direct experimental probe.

Indrajit Saha

LIGO-Virgo constraints on dark matter and leptogenesis triggered by a first order phase transition at high scale

We propose a minimal setup that realises dynamical inflection point inflation, and, using the same field content, generates neutrino masses, a baryon asymmetry of the universe, and dark matter. A dark SU(2) D  gauge sector with a dark scalar doublet playing the role of inflaton is considered along with several doublet and singlet fermions sufficient to realise multiple inflection points in the inflaton potential. The singlet fermions couple to SM leptons and generate neutrino masses via the inverse seesaw mechanism. Those fermions also decay asymmetrically and out of equilibrium, generating a baryon asymmetry via leptogenesis. Some of the fermion doublets are dark matter, and they are produced via inflaton decay and freeze-in annihilation of the same fermions that generate the lepton asymmetry. Reheating, leptogenesis, and dark matter are all at the TeV scale.

Canada

Daniel Stolarski

Dynamical inflation stimulated cogenesis

We study the phenomenology of leptophilic Z′ gauge bosons at the future high-energy e + e − and μ + μ − colliders, as well as at the gravitational wave observatories. The leptophilic Z′ model, although well-motivated, remains largely unconstrained from current low-energy and collider searches for Z′ masses above <math> <mi>O</mi> </math> $$ \mathcal{O} $$ (100 GeV), thus providing a unique opportunity for future lepton colliders. Taking <math> <mi>U</mi> <msub> <mfenced> <mn>1</mn> </mfenced> <mrow> <msub> <mi>L</mi> <mi>α</mi> </msub> <mo>−</mo> <msub> <mi>L</mi> <mi>β</mi> </msub> </mrow> </msub> </math> $$ \textrm{U}{(1)}_{L_{\alpha }-{L}_{\beta }} $$ (α, β = e, μ, τ) models as concrete examples, we show that future e + e − and μ + μ − colliders with multi-TeV center-of-mass energies provide unprecedented sensitivity to heavy leptophilic Z′ bosons. Moreover, if these U(1) models are classically scale-invariant, the phase transition at the U(1) symmetry-breaking scale tends to be strongly first-order with ultra-supercooling, and leads to observable stochastic gravitational wave signatures. We find that the future sensitivity of gravitational wave observatories, such as advanced LIGO-VIRGO and Cosmic Explorer, can be complementary to the collider experiments, probing higher Z′ masses up to <math> <mi>O</mi> </math> $$ \mathcal{O} $$ (104 TeV), while being consistent with naturalness and perturbativity considerations.

P. Dev

Rojalin Padhan

Si Wang

Searching for heavy leptophilic Z′: from lepton colliders to gravitational waves

We propose a novel framework where baryon asymmetry of the Universe can arise due to forbidden decay of dark matter (DM) enabled by finite-temperature effects in the vicinity of a first-order phase transition (FOPT). In order to implement this novel cogenesis mechanism, we consider the extension of the standard model by one scalar doublet <math><mi>η</mi></math>, three right-handed neutrinos (RHNs), all odd under an unbroken <math><msub><mi>Z</mi><mn>2</mn></msub></math> symmetry, popularly referred to as the scotogenic model of radiative neutrino mass. While the lightest RHN <math><msub><mi>N</mi><mn>1</mn></msub></math> is the DM candidate and stable at zero temperature, there arises a temperature window prior to the nucleation temperature of the FOPT assisted by <math><mi>η</mi></math>, where <math><msub><mi>N</mi><mn>1</mn></msub></math> can decay into <math><mi>η</mi></math> and leptons, generating a nonzero lepton asymmetry which gets converted into baryon asymmetry subsequently by sphalerons. The requirement of successful cogenesis together with a first-order electroweak phase transition not only keeps the mass spectrum of new particles in the sub-TeV ballpark within reach of collider experiments, but also leads to observable stochastic gravitational wave spectrum which can be discovered in planned experiments like the Laser Interferometer Space Antenna.

Baryon asymmetry from dark matter decay in the vicinity of a phase transition

We study a class of leptogenesis scenarios with decay or scattering being the source of lepton asymmetry, which can not only give rise to the observed baryon asymmetry in the Universe but also can leave behind a large remnant of neutrino asymmetry. Such large neutrino asymmetry can not only be probed at future cosmic microwave background experiments but is also motivating due to its possible role in solving the recently reported anomalies in <math><mrow><mmultiscripts><mrow><mi>He</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>4</mn></mrow></mmultiscripts></mrow></math> measurements. Additionally, such large neutrino asymmetry also offers the possibility of cogenesis if dark matter is in the form of a sterile neutrino resonantly produced in the early Universe via Shi-Fuller mechanism. Considering <math><mrow><mn>1</mn><mo>→</mo><mn>2</mn></mrow></math>, <math><mrow><mn>1</mn><mo>→</mo><mn>3</mn></mrow></math>, as well as <math><mn>2</mn><mo>→</mo><mn>2</mn></math> processes to be responsible for generating the asymmetries, we show that only TeV scale leptogenesis preferably of <math><mn>1</mn><mo>→</mo><mi>N</mi><mo>(</mo><mi>N</mi><mo>≥</mo><mn>3</mn><mo>)</mo></math> type can generate the required lepton asymmetry around sphaleron temperature while also generating a large neutrino asymmetry <math><mo>∼</mo><mi>O</mi><mo>(</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>2</mn></mrow></msup><mo>)</mo></math> by the epoch of the big bang nucleosynthesis. While such low scale leptogenesis can have tantalizing detection prospects at laboratory experiments, the indication of a large neutrino asymmetry provides a complementary indirect signature.