<p>We discuss a model of neutrino mass based on the type I seesaw mechanism embedded in a spontaneously broken global lepton number framework with a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>Z</mi><mn>2</mn></msub></math> symmetry. We show that the resulting Majoron is a viable freeze-in dark matter candidate. Two right-handed neutrinos are assumed to have dominant off-diagonal masses suggesting resonant leptogenesis as the origin of baryon asymmetry of the Universe. Explicit higher dimensional lepton number violating operators are shown to play a crucial role in simultaneously controlling both the Majoron production in the early Universe and the right handed neutrino mass splitting relevant for resonant leptogenesis. We perform a combined analysis of Majoron dark matter and leptogenesis, discussing the relative importance of self-energy and vertex contributions to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math> asymmetry, and explore the parameter space, leading to an intricate relation between neutrino mass, dark matter, and baryon asymmetry.</p>

United Kingdom

Stephen F. King

India

Soumen Kumar Manna

Rishav Roshan

Arunansu Sil

Leptogenesis with Majoron dark matter

We show that a phase transition may take place in the early Universe at a temperature <math><msub><mi>T</mi><mo>*</mo></msub></math> resulting a temperature dependent mass for right-handed neutrinos (RHN) which finally relaxes to a constant value after electroweak symmetry breaking (EWSB). As a result, a requisite amount of lepton asymmetry can be produced near <math><msub><mi>T</mi><mo>*</mo></msub></math> satisfying the observed baryon asymmetry of the Universe via the sphaleron process even when zero temperature masses of the RHNs fall below the electroweak scale enhancing the detection possibility of RHNs. Interestingly, the framework is also capable of predicting a primordial lepton asymmetry (generated after EWSB) as hinted by helium abundance measurements, indicating a correlation with the early phase of leptogenesis.

Dipendu Bhandari

South Korea

Arghyajit Datta

Leptogenesis from a phase transition in a dynamical vacuum

A derivative coupling of an axionlike particle (ALP) with a <math><mrow><mi>B</mi><mo>−</mo><mi>L</mi></mrow></math> current may lead to the baryon asymmetry of the Universe via spontaneous leptogenesis provided a lepton number breaking interaction prevails in thermal equilibrium. Conventionally, such scenario works only for heavy ALPs and high reheating temperature due to the fact that the same lepton number breaking contribution is tied up with neutrino mass generation also. In this work, we propose inert Higgs doublet assisted lepton number violating operator to relieve such tension so as to generate lepton asymmetry (of freeze-in/out type) with a much lower reheating temperature that can accommodate light (sub-GeV) ALPs sensitive to current and future ALP searches.

Spontaneous leptogenesis with sub-GeV axionlike particles

The hybrid leptogenesis framework combining the type-I and type-II seesaw mechanisms for neutrino mass necessarily include scattering topologies involving both the scalar triplet and the right-handed neutrino. We demonstrate that a systematic inclusion of these mixed scatterings can significantly alter the evolution of the number densities exhibiting, up to a factor ten, deviation in the predicted asymmetry as demonstrated by our benchmark scenarios. We provide quantitative constraints on the degeneracy of the seesaw scales where the complete analysis becomes numerically significant, limiting the validity of leptogenesis being dominated by the lightest seesaw species only.

Rohan Pramanick

Tirtha Sankar Ray

Toward a more complete description of hybrid leptogenesis

Axionlike particles (ALPs), the pseudo Nambu-Goldstone bosons associated to the spontaneous breaking of global symmetry, have emerged as promising dark matter candidates. Conventionally, in the context of misalignment mechanism, the nonthermally produced ALPs happen to stay frozen due to Hubble friction initially, and at a later stage, they begin to oscillate (before matter-radiation equality) at characteristic frequencies defined by their masses and behaving like cold dark matter. In this work, we study the influence of electroweak symmetry breaking (EWSB), through a higher order Higgs portal interaction, on the evolution of ALPs. Such an interaction is found to contribute partially to the ALP’s mass during EWSB, thereby modifying oscillation frequencies during EWSB as well as impacting upon the existing correlation between the scale of symmetry breaking and their masses. The novelty of the work lies in broadening the relic satisfied parameter space so as to probe it in near future via a wide range of experiments.

Effects of electroweak symmetry breaking on axionlike particles as dark matter

We show that the process of noninstantaneous reheating during the postinflationary period can have a sizable impact on the charged lepton Yukawa equilibration temperature in the early Universe. This suggests reviewing the effects of lepton flavors in the leptogenesis scenario where the production and decay of right-handed neutrinos take place within this prolonged era of reheating. We find this observation has the potential to shift the flavor regime(s) of leptogenesis compared to the standard thermal scenario.

Effects of Reheating on Charged Lepton Yukawa Equilibration and Leptogenesis

We show that Majoron, the pseudo-Nambu-Goldstone boson resulting from the spontaneous breaking of global lepton number symmetry, can present itself as a viable freeze-in type of dark matter in a mass range <math><mi>O</mi></math>(keV–GeV), thanks to the explicit higher dimensional Lepton number breaking operator. Interestingly, the proposal is restricted within the simplest extension of the Standard Model with two singlet right-handed neutrinos and a singlet scalar so to address light neutrino mass and spontaneous breaking of lepton number symmetry, respectively. The desired amount of Majoron production takes place from the annihilations of right-handed neutrinos indicating an intriguing connection between neutrino physics and dark matter.

Majorons revisited: Light dark matter as a FIMP

Recently, it has been shown that the presence of a noninstantaneous era of reheating can significantly alter the charged lepton(s) equilibration temperature(s) which plays an important role in flavor leptogenesis. In this work, we extend the analysis to a more general situation where right-handed neutrinos (RHNs) are also produced from the decay of the inflaton. The presence of these RHNs along with the thermally generated ones (above its mass equivalent temperature only) redistributes different components of the energy density of the Universe during this reheating era, thereby affecting the charged lepton equilibration temperature (in addition to the Hubble effect) as well as the final reheating temperature <math><msub><mi>T</mi><mi>RH</mi></msub></math>. Taking both the effects into account, we find that the decay of the lightest RHN in the setup not only provides a platform to study flavor leptogenesis during reheating, but also an interesting framework of <math><mi>q</mi><mi>u</mi><mi>a</mi><mi>s</mi><mi>i</mi></math>-thermal leptogenesis emerges.

Flavor leptogenesis during the reheating era

We propose a minimal model based on lepton number symmetry (and violation), to address a common origin of baryon asymmetry, dark matter and neutrino mass generation. The model consists of a vectorlike fermion to constitute the dark sector, three right-handed neutrinos (RHNs) to dictate leptogenesis and neutrino mass, while an additional complex scalar is assumed to be present in the early Universe the decay of which produces both dark matter and RHNs via lepton number violating and lepton number conserving interactions respectively. Interestingly, the presence of the same scalar helps in making the electroweak vacuum stable until the Planck scale. The unnatural largeness and smallness of the parameters required to describe correct experimental limits are attributed to lepton number violation. The allowed parameter space of the model is illustrated via a numerical scan.

Subhaditya Bhattacharya

Spain

Drona Vatsyayan

Symmetry origin of baryon asymmetry, dark matter, and neutrino mass

A two-component scalar dark matter scenario comprising an additional scalar doublet and a <math><mi>Y</mi><mo>=</mo><mn>0</mn></math> scalar triplet is proposed. Key features of the ensuing dark matter phenomenology are highlighted with emphasis on interconversion between the two dark matter components. For suitable choices of the model parameters, we show that such interconversion can explain the observed relic abundance when the doublet dark matter component has mass in the desert region while the triplet component has sub-TeV mass. This finding is important in the context of such mass regions known to predict underabundant relic density for the stand-alone cases of the scalar doublet and triplet. In addition, we also show that the present scenario can stabilize the electroweak vacuum up to the Planck scale in the parameter space responsible for the requisite dark matter observables.