Electroweak Baryogenesis Mechanism Research Articles

Nu Electroweak baryogenesis: the scalar singlet strikes back

We perform a comprehensive scan of the parameter space of a general singlet scalar extension of the Standard Model to identify the regions which can lead to a strong first-order phase transition, as required by the electroweak baryogenesis mechanism. We find that taking into account bubble nucleation is a fundamental constraint on the parameter space and present a conservative and fast estimate for it so as to enable efficient parameter space scanning. The allowed regions turn out to be already significantly probed by constraints on the scalar mixing from Higgs signal strength measurements. We also consider the addition of new neutrino singlet fields with Yukawa couplings to both scalars and forming heavy (pseudo)-Dirac pairs, as in the linear or inverse Seesaw mechanisms for neutrino mass generation. We find that their inclusion does not alter the allowed parameter space from early universe phenomenology in a significant way. Conversely, there are allowed regions of the parameter space where the presence of the neutrino singlets would remarkably modify the collider phenomenology, yielding interesting new signatures in Higgs and singlet scalar decays.

A Survey of Schematic of Vacuum Quantum Structure: General Equation for EBSF (III)

Researchers have studied the tiny effects on fundamental particles with quantum vacuum about electroweak baryogenesis mechanism, and so we can further confirm the existence of the energy basic state field of the universe (EBSF). In this paper, we propose that since EBSF is the basic energy field of the universe, the quantum superfluid state must be the next level of fundamental particle (quantum state). Then, the evolution-developed equation of quantum superfluid state should be nonlinear, which can be expressed by the fraction fractal KdV equation temporarily. This paper reviews the experimental observation of superfluid in the existing physics and puts forward the possible quantized form of KdV equation. One possible form of quantization for vortex line of quantum superfluid is the string theory, so the basic physical scenario and foundation of physics in string theory can be revealed. At the same time, through the analysis of the KdV equation and general solution, the quantum superfluid state as the lowest level physical state in physics can only be described by the topological invariant in topological theory, and its image is not uniform; there are common phenomena such as energy gap, non-closure and wrinkle (folding) in Euclidean space. Based on the physical view of the formation of the universe system, the idea of nonlinear evolution development, and the idea of level emergence theory in condensed matter physics, the authors preliminarily put forward the framework of the hierarchy theory of physics. The paper also analyzes the broad physical prospect of quantum superfluid physics (or new physics). The essence of some physics concepts is further clear, some present physics puzzles that are expected to be solved, but their mathematical physical processing has considerable complexity, and some rigorous proofs need further breakthroughs.

Dirac dark matter, neutrino masses, and dark baryogenesis

We present a gauged baryon number model as an example of models where all new fermions required to cancel out the anomalies help to solve phenomenological problems of the standard model (SM). Dark fermion doublets, along with the iso-singlet charged fermions, in conjunction with a set of SM-singlet fermions, participate in the generation of small neutrino masses through the Dirac-dark Zee mechanism. The other SM-singlets explain the dark matter in the Universe, while their coupling to an inert singlet scalar is the source of the $CP$ violation. In the presence of a strong first-order electroweak phase transition, this "dark" $CP$ violation allows for a successful electroweak baryogenesis mechanism.

Dark CP violation and gauged lepton or baryon number for electroweak baryogenesis

We explore the generation of the baryon asymmetry in an extension of the Standard Model where the lepton number is promoted to a $U(1)_\ell$ gauge symmetry with an associated $Z^\prime$ gauge boson. This is based on a novel electroweak baryogenesis mechanism first proposed by us in Ref. \cite{Carena:2018cjh}. Extra fermionic degrees of freedom - including a fermionic dark matter $\chi$ - are introduced in the dark sector for anomaly cancellation. Lepton number is spontaneously broken at high scale and the effective theory, containing the Standard Model, the $Z^\prime$, the fermionic dark matter, and an additional complex scalar field $S$, violates CP in the dark sector. The complex scalar field couples to the Higgs portal and is essential in enabling a strong first order phase transition. Dark CP violation is diffused in front of the bubble walls and creates a chiral asymmetry for $\chi$, which in turn creates a chemical potential for the Standard Model leptons. Weak sphalerons are then in charge of transforming the net lepton charge asymmetry into net baryon number. We explore the model phenomenology related to the leptophilic $Z^\prime$, the dark matter candidate, the Higgs boson and the additional scalar, as well as implications for electric dipole moments. We also discuss the case when baryon number $U(1)_B$ is promoted to a gauge symmetry, and discuss electroweak baryogenesis and its corresponding phenomenology.

CP violation at the finite temperature

In this letter we explore the CP violation at the finite temperature. We show that a spontaneous CP-violating phase φ may arise at the temperature of the electroweak phase transition, and φ can provide a source term for generating the matter-antimatter asymmetry of the universe via the electroweak baryogenesis mechanism (EWBG) whenever the domain wall relating to ±φ vacua is collapsed by a small explicit Z2-breaking term. Therefore no extra CP violation is needed! We further point out that this CP symmetry can be restored after the electroweak phase transition, such that there will be no constraint from the electric dipole moment (EDM) measurements. This study solves the tension between the non-observation of EDMs in precision measurement experiments and the requirement of a large CP violation by the EWBG.

Electroweak Baryogenesis from Dark-Sector CP Violation.

We present a novel mechanism of electroweak baryogenesis where CP violation occurs in a dark sector, comprised of standard model gauge singlets, thereby evading the strong electric dipole moment constraints. In this framework, the background of the timelike component of a new gauge boson Z_{μ}^{'}, generated at electroweak temperatures, drives the electroweak sphaleron processes to create the required baryon asymmetry. We first discuss the crucial ingredients for this mechanism to work, and then show that all of them can be elegantly embedded in ultraviolet completions with a spontaneously broken gauged lepton number. The models under consideration have a rich phenomenology and can be experimentally probed in leptophilic Z^{'} searches, dark matter searches, heavy Majorana neutrino searches, as well as through hunting for new Higgs portal scalars in multilepton channels at colliders.

Electroweak baryogenesis via chiral gravitational waves

We propose a new mechanism for electroweak baryogenesis based on gravitational waves generated by helical magnetic fields that are present during a first order electroweak phase transition. We generate a net lepton number through the gravitational chiral anomaly which appears due to the chiral gravitational waves produced by these magnetic fields. The observed value of baryon asymmetry can be obtained in our mechanism within parameter space of scenarios with an inverse cascade evolution for magnetic fields which can also be candidates for large-scale magnetic fields.

The origin of baryonic matter in the Universe

The origin of the matter-antimatter asymmetry in the Universe is a long-standing cosmological puzzle remaining to be solved. This slight excess of the baryonic matter is a key input to the big bang nucleosynthesis and therefore is responsible for the generation of the light elements in the early universe and finally the formation of stars and galaxies at a later time. This excess has been measured in several different ways. In particular, the value of this number has been precisely measured from studies of the temperature an-isotropies in the cosmic microwave background radiation by the Planck collaboration. Despite the concordance of the experimental measurements of this excess from different independent studies, none of the theoretical explanation of this problem is satisfactory and well accepted. The theoretical explanations of the baryon asymmetry are reviewed in this article. While there are many baryogenesis mechanisms, we focus on the mechanism of electroweak baryogenesis, which is a highly testable scenario and is within the reach of current high energy colliders. The physical picture of the mechanism of electroweak baryogenesis is then discussed. This is an interdisciplinary research area closely related to cosmology and the fundamental theory governing the particle physics. Therefore solutions to this cosmological problem may shed light on the searches for new physics governing particle interactions at the high energy frontier as well as the low energy intensity frontier. In particular, the necessity of going beyond the standard model of particle physics is discussed, due to the incapability of the standard model to generate the observed baryon asymmetry, with the solution of resorting to new physics capable of incorporating a new source of CP-violation and a Higgs potential that can accommodate a strongly first order electroweak phase transition. These requirements call for new particle interactions beyond the standard model and therefore can provide additional insight on new physics searches at high energy colliders and low energy precision measurements such as the searches for electric dipole moments of electrons, neutrons, protons and atoms. Also briefly discussed is the physical opportunities associated with the stochastic gravitational waves generated from a first order electroweak phase transition, which is another emerging window for probing the mechanism of electroweak symmetry breaking and therefore can provide another independent test of the mechanism of electroweak baryogenesis. The possibility of primordial black hole formation from the first order phase transition, which can serve as a non-particle candidate for the dark matter, and its possible detection with gravitational waves is also briefly introduced.

Gravitational wave signals of electroweak phase transition triggered by dark matter

We study in this work a scenario that the universe undergoes a two step phase transition with the first step happened to the dark matter sector and the second step being the transition between the dark matter and the electroweak vacuums, where the barrier between the two vacuums, that is necessary for a strongly first order electroweak phase transition (EWPT) as required by the electroweak baryogenesis mechanism, arises at the tree-level. We illustrate this idea by working with the standard model (SM) augmented by a scalar singlet dark matter and an extra scalar singlet which mixes with the SM Higgs boson. We study the conditions for such pattern of phase transition to occur and especially for the strongly first order EWPT to take place, as well as its compatibility with the basic requirements of a successful dark matter, such as observed relic density and constraints of direct detections. We further explore the discovery possibility of this pattern EWPT by searching for the gravitational waves generated during this process in spaced based interferometer, by showing a representative benchmark point of the parameter space that the generated gravitational waves fall within the sensitivity of eLISA, DECIGO and BBO.

750 GeV diphoton excess and strongly first-order electroweak phase transition

A new scalar particle, coupled to photons and gluons via loops of vector-like quarks, provides a simple theoretical interpretation of the 750 GeV diphoton excess reported by the experiments at the Large Hadron Collider (LHC). In this paper, we show that this model contains a large, phenomenologically viable parameter space region in which the electroweak phase transition (EWPT) is strongly first-order, opening the possibility that electroweak baryogenesis mechanism can be realized in this context. A large coupling between the Higgs doublet and the heavy scalar, required for a strongly first-order EWPT, can arise naturally in composite Higgs models. The scenario makes robust predictions that will be tested in near-future experiments. The cross section of resonant di-Higgs production at the 13 TeV LHC is predicted to be at least 20 fb, while the Higgs cubic self-coupling is enhanced by 40% or more with respect to its Standard Model (SM) value.

Impact of a complex singlet: Electroweak baryogenesis and dark matter

With the assistance of a complex singlet, and an effective operator involving CP violations, the dark matter relic abundance and baryon asymmetry of the universe have been addressed simul- taneously. We studied the electroweak baryogenesis mechanism systematically. The electroweak phase transition analysis indicates that the strong first order phase transition takes place by one- step or two-step type due to the dynamics of the energy gap between the electroweak vacuum and the vacuum of the complex singlet. The relation between the magnitude of baryon asymmetry of the universe and the phase transition type and strength has been explored in the framework of electroweak baryogenesis.

Electroweak baryogenesis in the exceptional supersymmetric standard model

We study electroweak baryogenesis in the E6 inspired exceptional supersymmetric standard model (E6SSM). The relaxation coefficients driven by singlinos and the new gaugino as well as the transport equation of the Higgs supermultiplet number density in the E6SSM are calculated. Our numerical simulation shows that both CP-violating source terms from singlinos and the new gaugino can solely give rise to a correct baryon asymmetry of the Universe via the electroweak baryogenesis mechanism.

First order electroweak phase transition triggered by the Higgs portal vector dark matter

We investigate an extension of the Standard Model (SM) with a U(1)' gauge symmetry, which is spontaneously broken by a complex scalar singlet and where the new gauge boson is a stable dark matter candidate via a Z2 flavor symmetry. The possibility of generating a strongly first order electroweak phase transition (EWPT) needed for the electroweak baryogenesis mechanism in this model is studied using a gauge independent method. Our result shows a considerable parameter space where both successful dark matter phenomenologies and a strongly first order EWPT can be achieved.

Supersonic electroweak baryogenesis: achieving baryogenesis for fast bubble walls

Standard electroweak baryogenesis in the context of a first order phase transition is effective in generating the baryon asymmetry of the universe if the broken phase bubbles expand at subsonic speed, so that CP asymmetric currents can diffuse in front of the wall. Here we present a new mechanism for electroweak baryogenesis which operates for supersonic bubble walls. It relies on the formation of small bubbles of the symmetric phase behind the bubble wall, in the broken phase, due to the heating of the plasma as the wall passes by. We apply the mechanism to a model in which the Higgs field is coupled to several singlets, and find that enough baryon asymmetry is generated for reasonable values of the parameter space.

Dark Matter candidates in a baryogenesis inspired scenario

It has recently been shown that the electroweak baryogenesis mechanism is feasible in Standard Model extensions containing extra fermions with large Yukawa couplings. We show that the lightest of these fermionic fields can naturally be a good candidate for cold dark matter. We find regions in the parameter space where the thermal relic abundance of this particle is compatible with the dark matter density of the Universe as determined by the WMAP experiment. We study direct and indirect dark matter detection for this model and compare with current experimental limits and prospects for upcoming experiments. We find, contrary to the standard lore, that indirect detection searches are more promising than direct ones, and they already exclude part of the parameter space.

Electroweak baryogenesis, large Yukawas and dark matter

It has been recently shown that the electroweak baryogenesis mechanism is feasible in Standard Model extensions containing extra fermions with large Yukawa couplings. We show here that the lightest of these fermionic fields can naturally be a good candidate for cold dark matter. We find regions in the parameter space where the thermal relic abundance of this particle is compatible with the dark matter density of the Universe as determined by the WMAP experiment. We study direct and indirect dark matter detection for this model and compare with current experimental limits and prospects for upcoming experiments. We find, contrary to the standard lore, that indirect detection searches are more promising than direct detection ones, and they already exclude a portion of the parameter space.

Electroweak baryogenesis and new TeV fermions

New fermions, strongly coupled to the standard model Higgs boson, provide a well motivated extension of the standard model (SM). In this work we show that, once new physics at heavier scales is added to stabilize the Higgs potential, such an extension of the SM can strengthen the first-order electroweak phase transition and make the electroweak baryogenesis mechanism feasible. We propose a SM extension with TeV Higgsinos, Winos and Binos that satisfy the following properties: (a) The electroweak phase transition is strong enough to avoid sphaleron erasure in the broken phase for values of the Higgs mass m H ≲ 300 GeV ; (b) It provides large CP-violating currents that lead to the observed baryon asymmetry of the Universe for natural values of the CP-violating phase; (c) It also provides a natural dark matter candidate that can reproduce the observed dark matter density; (d) It is consistent with electroweak precision measurements; (e) It may arise from a softly broken supersymmetric theory with an extra (asymptotically free) gauge sector; (f) It may be tested by electron electric dipole moment experiments in the near future.

Dark matter, light top squarks, and electroweak baryogenesis

We examine the neutralino relic density in the presence of a light top squark, such as the one required for the realization of the electroweak baryogenesis mechanism, within the minimal supersymmetric standard model. We show that there are three clearly distinguishable regions of parameter space, where the relic density is consistent with WMAP and other cosmological data. These regions are characterized by annihilation cross sections mediated by either light Higgs bosons, Z bosons, or by the co-annihilation with the lightest top squark. Tevatron collider experiments can test the presence of the light top squark in most of the parameter space. In the co-annihilation region, however, the mass difference between the light top squark and the lightest neutralino varies between 15 and 30 GeV, presenting an interesting challenge for top squark searches at hadron colliders. We present the prospects for direct detection of dark matter, which provides a complementary way of testing this scenario. We also derive the required structure of the high energy soft supersymmetry breaking mass parameters where the neutralino is a dark matter candidate and the top squark spectrum is consistent with electroweak baryogenesis and the present bounds on the lightest Higgs boson mass.

Improved results in supersymmetric electroweak baryogenesis

Electroweak baryogenesis provides a very attractive scenario to explain the origin of the baryon asymmetry. The mechanism of electroweak baryogenesis makes use of the baryon number anomaly and relies on physics that can be tested experimentally. It is today understood that, if the Higgs mass is not larger than 120 GeV, this mechanism may be effective within supersymmetric extensions of the Standard Model. In this work, we reconsider the question of baryon number generation at the electroweak phase transition within the context of the minimal supersymmetric extension of the Standard Model. We derive the relevant diffusion equations, give a consistent definition of the sources, and compare our results with those appearing in the recent literature on this subject.

Higgs-mediated electric dipole moments in the MSSM: an application to baryogenesis and Higgs searches

We perform a comprehensive study of the dominant two- and higher-loop contributions to the 205Tl, neutron and muon electric dipole moments induced by Higgs bosons, third-generation quarks and squarks, charginos and gluinos in the Minimal Supersymmetric Standard Model (MSSM). We find that strong correlations exist among the contributing CP-violating operators, for large stop, gluino and chargino phases, and for a wide range of values of tan β and charged Higgs-boson masses, giving rise to large suppressions of the 205Tl and neutron electric dipole moments below their present experimental limits. Based on this observation, we discuss the constraints that the non-observation of electric dipole moments imposes on the radiatively-generated CP-violating Higgs sector and on the mechanism of electroweak baryogenesis in the MSSM. We improve previously suggested benchmark scenarios of maximal CP violation for analyzing direct searches of CP-violating MSSM Higgs bosons at high-energy colliders, and stress the important complementary rôle that a possible high-sensitivity measurement of the muon electric dipole moment to the level of 10 −24 e cm can play in such analyses.