Leptogenesis Mechanism Research Articles

Conversion-Driven Leptogenesis: A Testable Theory of Dark Matter and Baryogenesis at the Electroweak Scale.

The phenomena of dark matter and the baryon asymmetry pose two of the most pressing questions in today's fundamental physics. Conversion-driven freeze-out has emerged as a successful mechanism to generate the observed dark matter relic density. It supports thermalization of dark matter despite its very weak couplings, aligning with the null results from direct and indirect detection experiments. In this Letter, we demonstrate that the departure from equilibrium of dark matter, induced by semi-efficient conversions, satisfies Sakharov's conditions, providing a novel explanation for both dark matter and the baryon asymmetry. Specifically, for a leptophilic model, we establish the mechanism of conversion-driven leptogenesis. The scenario predicts dark matter masses close to the electroweak scale offering testable predictions, such as soft displaced leptons at the LHC and future colliders.

Complete study of RG evolution induced leptogenesis in flavor symmetry scenarios

In the literature, motivated by the observed peculiar neutrino mixing pattern and a preliminary experimental hint for maximal Dirac CP phase (i.e., δ∼3π/2), a lot of flavor and CP symmetries have been proposed to help us understand and explain these experimental results. However, for some flavor-symmetry scenarios (see section motivations of our study), the leptogenesis mechanism is prohibited from working as usual. To tackle this problem, in this paper we have made an exhaustive study of the possibility that the renormalization group evolution effect may induce a successful leptogenesis for these particular scenarios. Our study provides complementarities to the previous related studies in Xing and Zhang, []; Xing and Zhang, []; and Cooper , [] (see section complementarities of our study to previous related studies). Published by the American Physical Society 2024

Common origin of dark matter and leptogenesis in U(1)B−L

In this paper, we investigate the common parameter space of dark matter and leptogenesis in the U(1)B−L symmetry. This model involves a complex scalar ϕ, sterile neutrinos N, and Majorana dark matter χ, where only dark matter χ is charged under the Z2 symmetry. Masses of N and χ are generated via the Yukawa interactions to ϕ after breaking of the U(1)B−L symmetry. TeV scale sterile neutrinos N are responsible for the generation of baryon asymmetry through the resonance leptogenesis mechanism. The new particles in the U(1)B−L have a significant impact on the dilution of N, thus on leptogenesis. Meanwhile, the annihilation processes of dark matter χ are almost identical to that of N, which indicates that both leptogenesis and dark matter are closely related to satisfying the observed results simultaneously. Under various theoretical and experimental constraints, the viable common parameter space of dark matter and leptogenesis is obtained for both global and local U(1)B−L symmetry.

Leptogenesis effects on the gravitational waves background:interpreting the NANOGrav measurements and JWST constraints on primordialblack holes

We demonstrate that the leptogenesis mechanisms, which are associated with B-L symmetry breaking mechanism has notable effects on the production of gravitational waves. These gravitational waves align well with the recent observations of a stochastic gravitational wave background by NANOGrav and pulsar-timing arrays (PTAs). For these gravitational waves to match the recent measurements, the critical value of the B-L breaking should be around the GUT scale. Moreover, we consider the generation of primordial gravitational waves from binary systems of Primordial Black Holes (PBHs) which could be predicted by the recent detection of gravitational waves. PBHs with specific masses can be responsible for massive galaxy formation observed at high redshifts reported by the James Webb Space Telescope (JWST). We contemplate the potential for a shared source between the NANOGrav and JWST observations, namely primordial black holes. These black holes could serve as seeds of rapid galaxy formation, offering an explanation for the galaxies observed by JWST.

Neutrino model with broken [formula omitted] -[formula omitted] symmetry and unflavored leptogenesis with dihedral flavor symmetry

We propose a new neutrino flavor model based on a D4×U(1) flavor symmetry providing predictions for neutrino masses and mixing along with a successful generation of the observed Baryon Asymmetry of the Universe (BAU). After the spontaneous breaking of the flavor symmetry, the type I seesaw mechanism leads to a light neutrino mass matrix with broken μ−τ symmetry. By performing a numerical analysis, we find that the model favors a normal mass hierarchy with the lightest neutrino mass lies in the range m1∈[2.516,21.351] meV. The phenomenological implications of the neutrino sector are explored in detail and the results are discussed. Moreover, the generation of BAU is addressed via the leptogenesis mechanism from the decay of three right-handed neutrinos Ni. Through analytical and numerical analysis of the baryon asymmetry parameter YB, a successful unflavored leptogenesis takes place within the allowed parameter space obtained from neutrino phenomenology. We also examine interesting correlations between YB and low energy observables and provide a comprehensive discussion of the results.

Parameter space of leptogenesis in polynomial inflation

Polynomial inflation is a very simple and well motivated scenario. A potential with a concave “almost” saddle point at field value ϕ = ϕ 0 fits well the cosmic microwave background (CMB) data and makes testable predictions for the running of the spectral index and the tensor to scalar ratio. In this work we analyze leptogenesis in the polynomial inflation framework. We delineate the allowed parameter space giving rise to the correct baryon asymmetry as well as being consistent with data on neutrino oscillations. To that end we consider two different reheating scenarios. (i) If the inflaton decays into two bosons, the reheating temperature can be as high as T rh ∼ 1014 GeV without spoiling the flatness of the potential, allowing vanilla N 1 thermal leptogenesis to work if T rh > M 1 where N 1 is the lightest right-handed neutrino and M 1 its mass. Moreover, if the dominant decay of the inflaton is into Higgs bosons of the Standard Model, we find that rare three-body inflaton decays into a Higgs boson plus one light and one heavy neutrino allow leptogenesis even for T rh < M 1 if the inflaton mass is of order 1012 GeV or higher; in the polynomial inflation scenario this requires ϕ 0 ≳ 2.5 MP . This novel mechanism of non-thermal leptogenesis is quite generic, since the coupling leading to the three-body final state is required in the type I see-saw mechanism. (ii) If the inflaton decays into two fermions, the flatness of the potential implies a lower reheating temperature. In this case inflaton decay to two N 1 still allows successful non-thermal leptogenesis if ϕ 0 ≳ 0.1 MP and T rh ≳ 106 GeV.

Standard and Non-Standard Aspects of Neutrino Physics

This review provides a succinct overview of the basic aspects of neutrino physics. The topics covered include neutrinos in the standard model and the three-neutrino mixing scheme; the current status of neutrino oscillation measurements and what remains to be determined; the seesaw mechanisms for neutrino mass generation and the associated phenomenology, including the leptogenesis mechanism to explain the observed matter–antimatter asymmetry of the Universe; and models for the origin of the pattern of neutrino mixing and lepton masses based on discrete flavour symmetries and modular invariance.

Parity solution to the strong CP problem and a unified framework for inflation, baryogenesis, and dark matter

It has been known for some time that asymptotic parity invariance of weak interactions can provide a solution to the strong CP problem without the need for the axion. Left-right symmetric theories which employ a minimal Higgs sector consisting of a left-handed and a right-handed doublet is an example of such a theory wherein all fermion masses arise through a generalized seesaw mechanism. In this paper we present a way to understand the origin of matter-antimatter asymmetry as well as the dark matter content of the universe in these theories using the Affleck-Dine (AD) leptogenesis mechanism and inflaton decay, respectively. Three gauge singlet fermions are needed for this purpose, two of which help to implement the Dirac seesaw for neutrino masses while the third one becomes the non-thermal dark matter candidate. A soft lepton number breaking term involving the AD scalar field is used to generate lepton asymmetry which suffers no wash-out effects and maintains the Dirac nature of neutrinos. This framework thus provides a unified description of many of the unresolved puzzles of the standard model that require new physics.

Anomalies, the Dark Universe and Matter-Antimatter asymmetry

I review a (3+1)-dimensional, string-inspired cosmological model with gravitational anomalies (of Chern-Simons (CS) type) at early epochs, and a totally-antisymmetric torsion, dual to a massless axion-like field (“gravitational axion”), which couples to the CS term. Under appropriate conditions, primordial gravitational waves can condense, leading to a condensate of the CS anomaly term. As a consequence, one obtains inflation in this theory, of running-vacuum-model (RVM) type, without the need for external inflatons. At the end of the inflationary era, chiral fermionic matter is generated, whose gravitational anomalies cancel the primordial ones. On the other hand, chiral anomalies of gauge type, which are also generated by the chiral matter, remain present during the post-inflationary epochs and become responsible for the generation of a non-perturbative mass for the torsion-related gravitational axion, which, in this way, might play the rôle of a Dark Matter component of geometrical origin. Moreover, in this model, stringy non-perturbative effects during the RVM inflationary phase generate periodic structures for the potential of axion-like particles that arise due to compactification, and co-exist with the gravitational axions. Such periodic potential modulations may lead to an enhanced production of primordial black holes during inflation, which in turn affects the profile of the generated gravitational waves during the radiation era, with potentially observable consequences. This model also entails an unconventional mechanism for Leptogenesis, due to Lorentz-violating backgrounds of the gravitational axions that are generated during inflation, as a consequence of the anomaly condensates, and remain undiluted in the radiation era.

Gravitational leptogenesis from metric perturbations

In this work, we make the observation that the gravitational leptogenesis mechanism can be implemented without invoking new axial couplings in the inflaton sector. We show that, in the perturbed Robertson-Walker background emerging after inflation, the spacetime metric itself breaks parity symmetry and generates a nonvanishing Pontryagin density which can produce a matter-antimatter asymmetry. We analyze the produced asymmetry in different inflationary and reheating scenarios. We show that the generated asymmetry can be locally comparable to observations in certain cases, although the size of the matter-antimatter regions is typically much smaller than the present Hubble radius.

Explaining the CDF-II W-boson mass anomaly in the Georgi–Machacek extension models

Original Georgi–Machacek model can preserve the custodial symmetry at tree level after the electroweak symmetry breaking. Unless additional SU(2)_c custodial symmetry breaking effects are significant, the new physics contributions to Delta m_W are always very small. Our numerical results show that ordinary GM model can contribute to Delta m_W a maximal amount 0.0012 GeV, which can not explain the new CDF-II anomaly on W boson mass. We propose firstly to introduce small misalignment among the triplet VEVs to increase Delta m_W, which can give large new physics contributions to Delta m_W. Such slightly misaligned triplet VEVs from custodial symmetry preserving scalar potential can still be allowed. Our numerical results indicate that the resulting Delta m_W can easily reach the 1sigma range of CDF-II m_W data and the splitting among the triplet VEVs Delta v(equiv v_xi -v_chi ) can be as small as 0.8 GeV for v_chi lesssim 15 GeV. We also propose to introduce an additional custodial symmetry breaking source by extending the GM model with a low scale RH neutrino sector, which can adopt the leptogenesis mechanism and allow moderately large coupling strength h_{ij} even for triplet VEVs of order GeV. With low scale RH neutrino mass scale of order 10^2–10^4 TeV, the new physics contribution to Delta m_W can reach 0.03 GeV and is much larger than that of ordinary GM model. Combining both custodial SU(2)_c symmetry breaking effects, the small misalignment among the triplet VEVs and the moderately large h_{ij} couplings allowed with RH neutrino sector, the value of Delta m_W can still easily reach the 1sigma range of CDF-II m_W data, with a minimum splitting (among the triplet VEVs) approximately 0.7 GeV for v_chi lesssim 15 GeV.

Leptogenesis triggered by a first-order phase transition

We propose a new scenario of leptogenesis, which is triggered by a first-order phase transition (FOPT). The right-handed neutrinos (RHNs) are massless in the old vacuum, while they acquire a mass in the new vacuum bubbles, and the mass gap is huge compared with the FOPT temperature. The ultra-relativistic bubble walls sweep the RHNs into the bubbles, where the RHNs experience fast decay and generate the lepton asymmetry, which is further converted to the baryon asymmetry of the Universe (BAU). Since the RHNs are out of equilibrium inside the bubble, the generated BAU does not suffer from the thermal bath washout. We first discuss the general feature of such a FOPT leptogenesis mechanism, and then realize it in an extended B − L model. The gravitational waves from U(1)B−L breaking could be detected at the future interferometers.

Robustness of ARS leptogenesis in scalar extensions

Extensions of the Standard Model (SM) with sterile neutrinos are well motivated from the observed oscillations of the light neutrinos and they have shown to successfully explain the Baryon Asymmetry of the Universe (BAU) through, for instance, the so-called ARS leptogenesis. Sterile neutrinos can be added in minimal ways to the SM, but many theories exist where sterile neutrinos are not the only new fields. Such theories often include scalar bosons, which brings about the possibility of further interactions between the sterile neutrinos and the SM. In this paper we consider an extension of the SM with two sterile neutrinos and one scalar singlet particle and investigate the effect that an additional, thermalised, scalar has on the ARS leptogenesis mechanism. We show that in general the created asymmetry is reduced due to additional sterile neutrino production from scalar decays. When sterile neutrinos and scalars are discovered in the laboratory, our results will provide information on the applicability of the ARS leptogenesis mechanism.

Neutrino mass from Affleck-Dine leptogenesis and WIMP dark matter

Affleck-Dine (AD) mechanism for leptogenesis involves the cosmological evolution of a complex scalar field (AD field) that carries non-zero lepton number. We show how explicit lepton number breaking terms, which involve the AD field needed to implement this scenario combined with fermionic WIMP dark matter, can generate neutrino mass at the one loop level, thus providing a unified framework for solving four major puzzles of the standard model i.e. inflation, baryogenesis, dark matter and neutrino mass. We discuss some phenomenological implications of this model.

Baryogenesis from hierarchical Dirac neutrinos

We present here a novel and testable mechanism for leptogenesis, which is characterized by a purely thermal generation of lepton asymmetry via scalar decay. Guided by the thermal mass matrix diagonalization in the finite-temperature regime, we propose a scenario in which the baryon asymmetry is formulated in terms of the masses and mixing from hierarchical Dirac neutrinos, as well as a vacuum scale accountable for the sub-eV neutrino masses. This allows a natural and direct link between the high-scale \textit{CP} asymmetry and the low-energy Dirac \textit{CP}-violating phase without involved model structures, and thus circumvents the haunting problem encountered in general leptogenesis scenarios. The mechanism can also be applied as a prototype for solving the baryon asymmetry problem to a broad class of well-motivated model buildings.

Origin of neutrino masses and disappearance ofprimordial antimatter

<p indent="0mm">The standard model (SM) of particle physics has proved to be a huge success in describing the microscopic structures of matter and the behaviors of strong, weak and electromagnetic forces, but it is incomplete in some aspects. For example, the SM itself provides no answer about the origin of tiny neutrino masses, and it fails in accounting for the observed matter-antimatter asymmetry of the Universe. To go beyond the SM, one may wonder whether there exists an intrinsic connection between the solutions to these two fundamental issues in particle physics and cosmology. It is argued that the seesaw mechanism for neutrino mass generation and the associated leptogenesis mechanism for cosmological baryogenesis may pave a way for our deeper understanding of the origin of neutrino masses and mysterious disappearance of primordial antimatter of the Universe. Behind these two mechanisms is the existence of heavy and sterile Majorana neutrinos, which interact with the known (light and active) neutrinos via the Yukawa interactions. The SM contains no right-handed neutrino fields, and hence there is no way to write out a Dirac neutrino mass term. The simplest way to go beyond the SM is to introduce the right-handed neutrino fields and allow for lepton number violation. In this case the right-handed neutrino fields and their charge-conjugate counterparts may constitute a Majorana mass term which, together with the Yukawa interactions between left- and right-handed neutrino fields via the Higgs field, leads us to the origin of tiny Majorana masses for three active neutrinos. Such a seesaw mechanism attributes the smallness of active neutrino masses to the largeness of sterile neutrino masses as compared with the electroweak scale. The lepton-number-violating and CP-violating decays of those heavy degrees of freedom in the early Universe may produce a net lepton-antilepton asymmetry, and the latter may be partly converted into a net baryon-antibaryon asymmetry via the sphaleron process. This is just the leptogenesis mechanism, and it has attracted a lot of attention thanks to the observations of neutrino oscillations in the past decades. The seesaw and leptogenesis scenarios are correlated with each other, and they provide an elegant way of accounting for the cosmological baryon-antibaryon asymmetry and tiny neutrino masses. A pressing question is how to test such a “killing two birds with one stone” picture at low-energy experiments. It seems that a direct test of this picture is extremely difficult or even impossible, but one may always collect various “fossils” of heavy Majorana neutrinos which might have played a crucial role in the early Universe. In this connection it will be greatly helpful to verify the Majorana nature of massive neutrinos by observing the neutrinoless double-beta decays, to measure CP violation in neutrino oscillations and to test unitarity of the 3×3 flavor mixing matrix of three active neutrinos.

Leptogenesis, fermion masses and mixings in a SUSY SU(5) GUT with D4 flavor symmetry

We propose a model of fermion masses and mixings based on SU(5) grand unified theory (GUT) and a D4 flavor symmetry. This is a highly predictive 4D SU(5) GUT with a flavor symmetry that does not contain a triplet irreducible representation. The Yukawa matrices of quarks and charged leptons are obtained after integrating out heavy messenger fields from renormalizable superpotentials while neutrino masses are originated from the type I seesaw mechanism. The group theoretical factors from 24- and 45-dimensional Higgs fields lead to ratios between the Yukawa couplings in agreement with data, while the dangerous proton decay operators are highly suppressed. By performing a numerical fit, we find that the model captures accurately the mixing angles, the Yukawa couplings and the CP phase of the quark sector at the GUT scale. The neutrino masses are generated at the leading order with the prediction of trimaximal mixing while an additional effective operator is required to account for the baryon asymmetry of the universe (BAU). The model is remarkably predictive because only the normal neutrino mass ordering and the lower octant of the atmospheric angle are allowed while the CP conserving values of the Dirac neutrino phase δCP are excluded. Moreover, the predicted values of the effective Majorana mass mββ can be tested at future neutrinoless double beta decay experiments. An analytical and a numerical study of the BAU via the leptogenesis mechanism is performed. We focused on the regions of parameter space where leptogenesis from the lightest right-handed neutrino is successfully realized. Strong correlations between the parameters of the neutrino sector and the observed BAU are obtained.

Hilbert series for leptonic flavor invariants in the minimal seesaw model

In this paper, we examine the leptonic flavor invariants in the minimal see-saw model (MSM), in which only two right-handed neutrino singlets are added into the Standard Model in order to accommodate tiny neutrino masses and explain cosmological matter-antimatter asymmetry via leptogenesis mechanism. For the first time, we calculate the Hilbert series (HS) for the leptonic flavor invariants in the MSM. With the HS we demonstrate that there are totally 38 basic flavor invariants, among which 18 invariants are CP-odd and the others are CP-even. Moreover, we explicitly construct these basic invariants, and any other flavor invariants in the MSM can be decomposed into the polynomials of them. Interestingly, we find that any flavor invariants in the effective theory at the low-energy scale can be expressed as rational functions of those in the full MSM at the high-energy scale. Practical applications to the phenomenological studies of the MSM, such as the sufficient and necessary conditions for CP conservation and CP asymmetries in leptogenesis, are also briefly discussed.

Cosmological implications of a B − L charged hidden scalar: leptogenesis and gravitational waves * *The work of L.B. is Supported by the National Natural Science Foundation of China (12075041, 12047564), the Fundamental Research Funds for the Central Universities of China (2021CDJQY-011, 2020CDJQY-Z003), Chongqing Natural Science Foundation (cstc2020jcyj-msxmX0814). W.C. is Supported by the China Postdoctoral Science Foundation (2019TQ0329). H.G. is

In this study, we investigated the cosmological implications of a complex singlet scalar with non-trivial charges in the conformal theory. It was found that, in a sizable region of parameter space, may disturb the resonant leptogenesis mechanism, which is used to generate baryon asymmetry, and affect the symmetry breaking dynamics in the strong first order phase transition. The stochastic gravitational waves (GWs) produced at the phase transition can be probed in future GW experiments. The GW searches prefer a relatively light at the TeV-scale; however, this is difficult to detect directly at future high-energy colliders.

FIMP Dark Matter from Leptogenesis in Fast Expanding Universe

Within the framework of canonical type-I seesaw, a feebly interacting massive particle (FIMP) χ is introduced as a dark matter candidate. The leptogenesis mechanism and dark matter relic density share a common origin via decays of Majorana neutrinos N. Provided an additional species φ whose energy density red-shifts as ρφ ∝ a -(4+n), the Hubble expansion rate is larger than the standard scenario, i.e., the Universe expands faster. The consequences of such a fast expanding Universe (FEU) on leptogenesis as well as FIMP dark matter are investigated in detail. We demonstrate a significant impact on the final baryon asymmetry and dark matter abundance due to the existence of φ for the strong washout scenario. While for the weak washout scenario, the effects of FEU are relatively small. We introduce scale factors FL and F χ to describe the corresponding effects of FEU. A semi-analytical approach to derive the efficiency factors η L and ηχ in FEU is also discussed. The viable parameter space for success thermal leptogenesis and correct FIMP DM relic density is obtained for standard cosmology and FEU. Our results show that it is possible to distinguish different cosmology scenarios for strong washout cases.