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.

United Kingdom

Stephen F. King

India

Soumen Kumar Manna

Rishav Roshan

Arunansu Sil

Leptogenesis with Majoron dark matter

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

Debasish Borah

Amit Chakraborty

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

We calculate the gravitational waves (GWs) produced by primordial black holes (PBHs) in the presence of the inflaton condensate in the early Universe. Combining the GW production from the evaporation process, the gravitational scattering of the inflaton itself, and the density fluctuations due to the inhomogeneous distribution of PBHs, we propose for the first time a complete coherent analysis of the spectrum, revealing three peaks, one for each source. Three frequency ranges (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo>∼</mo><mi>kHz</mi></math>, GHz, and PHz, respectively) are expected, each giving rise to a similar GW peak amplitude <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi mathvariant="normal">Ω</mi><mi>GW</mi></msub></math>. We also compare our predictions with current and future GWs detection experiments.

France

Mathieu Gross

Yann Mambrini

Spain

Essodjolo Kpatcha

Maria Olalla Olea-Romacho

Gravitational wave production during reheating: From the inflaton to primordial black holes

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.

Nayan Das

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 scenario where a high scale seesaw origin of light neutrino mass and gravitational dark matter (DM) in MeV-TeV ballpark originating from primordial black hole (PBH) evaporation can be simultaneously probed by future observations of stochastic gravitational wave (GW) background with multiple tilts or spectral breaks. A high scale breaking of an Abelian gauge symmetry ensures the dynamical origin of the seesaw scale while also leading to the formation of cosmic strings responsible for generating stochastic GW background. The requirement of a correct DM relic in this ballpark necessitates the inclusion of a diluter as PBH typically leads to DM overproduction. This leads to a second early matter dominated epoch after PBH evaporation due to the long-lived diluter. These two early matter dominated epochs, crucially connected to the DM relic, lead to multiple spectral breaks in the otherwise scale-invariant GW spectrum formed by cosmic strings. We find interesting correlations between DM mass and turning point frequencies of GW spectrum which are within reach of several near future experiments like LISA, BBO, ET, CE, etc.

Suruj Jyoti Das

South Korea

Probing high scale seesaw and PBH generated dark matter via gravitational waves with multiple tilts

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.

Arghyajit Datta

Effects of Reheating on Charged Lepton Yukawa Equilibration and Leptogenesis

We explore how quantum gravity effects, manifested through the breaking of discrete symmetry responsible for both dark matter and domain walls, can have observational effects through cosmic microwave background observations and gravitational waves. To illustrate the idea we consider a simple model with two scalar fields and two <math><msub><mi>Z</mi><mn>2</mn></msub></math> symmetries, one being responsible for dark matter stability, and the other spontaneously broken and responsible for domain walls, where both symmetries are assumed to be explicitly broken by quantum gravity effects. We show the recent gravitational wave spectrum observed by several pulsar timing array projects can help constrain such effects.

Xin Wang

Graham White

Japan

Masahito Yamazaki

Quantum gravity effects on dark matter and gravitational waves

We propose a novel framework where baryon asymmetry can arise due to forbidden decay of dark matter (DM) enabled by finite-temperature effects in the early Universe. In order to implement it in a realistic setup, we consider the DM to be a singlet Dirac fermion that acquires a dark asymmetry from a scalar field <math><mi>Φ</mi></math> via the Affleck-Dine mechanism. Because of finite-temperature effects, DM can decay in the early Universe into leptons and a second Higgs doublet, thereby transferring a part of the dark asymmetry into lepton asymmetry, with the latter getting converted into baryon asymmetry subsequently via electroweak sphalerons. DM becomes stable below a critical temperature, leading to a stable relic. While the scalar field <math><mi>Φ</mi></math> can play the role of inflaton with specific predictions for inflationary parameters, the setup also remains verifiable via astrophysical as well as laboratory-based observations.

Baryon asymmetry from dark matter decay

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 study the effect of an ultralight primordial black hole (PBH) dominated phase on the gravitational wave (GW) spectrum generated by a cosmic string (CS) network formed as a result of a high-scale <math><mi>U</mi><mo>(</mo><mn>1</mn><mo>)</mo></math> symmetry breaking. A PBH-dominated phase leads to tilts in the spectrum via entropy dilution and generates a new GW spectrum from PBH density fluctuations, detectable at ongoing and planned near-future GW detectors. The combined spectrum has a unique shape with a plateau, a sharp tilted peak over the plateau, and a characteristic falloff, which can be distinguished from the one generated in the combination of CS and any other matter domination or new exotic physics. We discuss how ongoing and planned future experiments can probe such a unique spectrum for different values of <math><mi>U</mi><mo>(</mo><mn>1</mn><mo>)</mo></math> breaking scale and PBH parameters such as initial mass and energy fraction.