1,720,996 research outputs found
Spontaneous dark matter stability from a fermiophobic U(1)' gauge symmetry
No full textIn model building, discrete symmetries cannot only play an important role in preserving the structure of Yukawa interactions but also provide a pathway to stabilise dark matter candidates. However, such discrete symmetries are not necessarily be imposed directly by hand. Instead, they can arise from the spontaneous symmetry breaking (SSB) of continuous symmetries. As an example, we study the type Ib seesaw model, where the effective neutrino mass operator involves two different Higgs doublets and two right-handed (RH) neutrinos forming a single heavy Dirac pair. The heavy neutrino, together with the Higgs doublets, is charged under a U(1)′ gauge symmetry which helps to preserve the special structure of the type Ib seesaw mechanism. After the SSB, the U(1)′ symmetry turns into a Z2 symmetry which stabilises a dark matter candidate. The dark matter candidate interacts with the other particles in the thermal bath through the massive boson resulting from the U(1)′ symmetry breaking. We explore how the correct dark matter relic abundance can be produced thermally in both a low energy effective model and a renormalisable model with a complete fourth family of vector-like fermions
Brief on dark matter in the type Ib seesaw model: a GeV-scale Dirac neutrino portal
No full textThe type Ib seesaw, as an alternative explanation to the origin of neutrino mass, provides a new intriguing way to connect the neutrino physics to cosmology. In this proceeding, we consider a minimal type Ib seesaw model where the effective neutrino mass operator involves two different Higgs doublets and a heavy Dirac mass. We propose a minimal dark matter extension of this model, in which the Dirac heavy neutrino is coupled to a dark Dirac fermion and a dark complex scalar field, both odd under a discrete Z_2 symmetry, where the lighter one serves as a dark matter candidate. Focussing on the fermionic dark matter case, we explore the parameter space of the seesaw Yukawa couplings, the neutrino portal couplings and dark scalar to dark fermion mass ratio, where correct dark matter relic abundance can be produced by the freeze-in mechanism. By considering the mixing between the standard model neutrinos and the heavy neutrino, a connection can be built between dark matter production and laboratory experiments
Neutrino and Cosmology
No full textWe explore the connection between particle physics and cosmology, with a focus on neutrino related physics. Firstly, we study the neutrino portal dark matter extension of a concrete type I seesaw model. Since the dark matter candidate is superheavy in the model, the graviton mediated production can contribute significantly. To include the gravitational contribution, we study gravitational production in a Higgs portal scalar dark matter model as a prerequisite and then apply the method to neutrino portal dark matter.We then consider an alternative version of type I seesaw model, namely the type Ib seesaw model. Different from the traditional type I seesaw model, the model allow a connection between neutrino physics and dark matter problem at GeV scale and thus can be related to laboratory experiments. In order to explain the baryon asymmetry through leptogenesis, the model is extended with a superheavy right-handed neutrino which helps to realise the type Ib seesaw mechanism effectively at low energy. The model also provide us a new possibility of vector portal dark matter due to its unique nature of heavy Dirac neutrino. Lastly, we explore the connection between physics beyond the standard model and gravitational waves. In the framework of SO(10) grand unified theory, we considered a minimal model explaining fermion masses and mixing and baryon asymmetry, which can be tested by the next generation of gravitational wave detectors as well as neutrino oscillation experiments which will also constrain the proton lifetime. We also explore the possibility of detecting leptoquark through gravitational wave produced during a electroweak first-order phase transition
Gravitational wave signals from leptoquark-induced first order electroweak phase transitions
No full textWe consider the extension of the Standard Model (SM) with scalar leptoquarks in singlet, doublet and triplet representations. Through the coupling between leptoquark and the SM Higgs field, the electroweak phase transition (EWPT) can turn into first order and consequently produce gravitational wave signals. We compute the required value of the leptoquark-Higgs for first order EWPT to happen and discuss about the possible constraint from Higgs phenomenology. Choosing some benchmarks, we present the strength of the gravitational waves produced during the leptoquark-induced first order EWPT and compare them to detector sensitivities. We find that the representations of the leptoquark can be distinguished by gravitational waves in the parameter space where first order EWPT can happen as a function of the Higgs portal coupling
Gravitational wave signals from leptoquark-induced first-order electroweak phase transitions
No full textWe consider the extension of the Standard Model (SM) with scalar leptoquarks in SU(2) singlet, doublet and triplet representations. Through the coupling between leptoquark and the SM Higgs field, the electroweak phase transition (EWPT) can turn into first-order and consequently produce gravitational wave signals. We compute the required value of the leptoquark-Higgs for first-order EWPT to happen and discuss about the possible constraint from Higgs phenomenology. Choosing some benchmarks, we present the strength of the gravitational waves produced during the leptoquark-induced first-order EWPT and compare them to detector sensitivities. We find that the SU(2) representations of the leptoquark can be distinguished by gravitational waves in the parameter space where first-order EWPT can happen as a function of the Higgs portal coupling.</p
Leptogenesis in type Ib seesaw models
No full textWe study leptogenesis in three different realizations of the type Ib seesaw mechanism, where the effective masses of the neutrinos are obtained by the spontaneous symmetry breaking of two different Higgs doublets. In the minimal type Ib seesaw model, where two right-handed neutrinos form a Dirac mass, we show that it is impossible to produce the correct baryon asymmetry, even including a pseudo-Dirac mass splitting. In an extended type Ib seesaw model, with a third very heavy Majorana right-handed neutrino, together with the low-scale Dirac pair of right-handed (RH) neutrinos and an extra singlet Higgs boson, we find that the imbalance of matter and antimatter can be explained by resonant leptogenesis. In the resulting low-scale effective type Ib seesaw mechanism, we derive the allowed range of the seesaw couplings consistent with resonant leptogenesis. Dark matter may also be included via the right-handed neutrino portal. The Dirac RH neutrino masses may lie in the 1-100-GeV mass range, accessible to the future experiments Search for Hidden Particles (SHiP) and Future electron-positron Circular Collider (FCC-ee), allowing the type Ib seesaw mechanism with leptogenesis and dark matter to be tested.</p
Interplay between neutrino and gravity portals for FIMP dark matter
No full textIn the classic type I seesaw mechanism with very heavy right-handed (RH) neutrinos, it is possible to account for dark matter via RH neutrino portal couplings to a feebly interacting massive particle (FIMP) dark sector. However, for large RH neutrino masses, gravity can play an important role. We study the interplay between the neutrino portal through the right-handed neutrinos and the gravity portal through the massless spin-2 graviton in producing dark matter particles in the early universe. As a concrete example, we consider the minimal and realistic Littlest Seesaw model with two RH neutrinos, augmented with a dark scalar and a dark fermion charged under a global U(1)
D dark symmetry. In the model, the usual seesaw neutrino Yukawa couplings and the right-handed neutrino masses (the lightest being about 5×10
10 GeV) are fixed by neutrino oscillations data and leptogenesis. Hence, we explore the parameter space of the two RH neutrino portal couplings, the two dark particle masses and the reheating temperature of the universe, where the correct dark matter relic abundance is achieved through the freeze-in mechanism. In particular, we highlight which class of processes dominate the dark matter production. We find that, despite the presence of the gravity portal, the dark matter production relies on the usual seesaw neutrino Yukawa coupling in some regions of the parameter space, so realising a direct link between dark matter and neutrino phenomenology. Finally, we report the threshold values for the neutrino portal couplings below which the neutrino portal is irrelevant and the Planckian Interacting Dark Matter paradigm is preserved.
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Minimal multi-majoron model
No full textIn order to provide a natural framework for hierarchical right-handed neutrinos, we propose a realistic ultraviolet complete minimal multi-Majoron model (MMMM). We consider two right-handed neutrinos for simplicity, although the model is readily extendable to more. The minimal model introduces two complex scalar Majoron fields ϕ1 and ϕ2, whose couplings to the two respective right-handed neutrinos are controlled by an extra global U(1)N symmetry. We show that a flavon field is required to facilitate the effective Yukawa couplings, in order to implement the type I seesaw mechanism. We analyse the resulting phenomenology related to neutrino masses, flavour mixing and cosmological predictions concerning the formation and decay of topological defects like the global cosmic strings and the domain walls when the U(1)N × U(1)B−L symmetry is broken. The resulting gravitational wave spectrum is a distinctive combination of the spectrum from the global cosmic string and strong first-order phase transitions when the symmetries are broken, the strength of the latter being enhanced by the second Majoron field. The resulting characteristic spectrum determines the two right-handed neutrino mass scales within the considered framework
Dark matter in the Type Ib seesaw model
No full textWe consider a minimal type Ib seesaw model where the effective neutrino mass operator involves two different Higgs doublets, and the two right-handed neutrinos form a heavy Dirac mass. We propose a minimal dark matter extension of this model, in which the Dirac heavy neutrino is coupled to a dark Dirac fermion and a dark complex scalar field, both charged under a discrete symmetry, where the lighter of the two is a dark matter candidate. Focussing on the fermionic dark matter case, we explore the parameter space of the seesaw Yukawa couplings, the neutrino portal couplings and dark scalar to dark fermion mass ratio, where correct dark matter relic abundance can be produced by the freeze-in mechanism. By considering the mixing between between the standard model neutrinos and the heavy neutrino, we build a connection between the dark matter production and current laboratory experiments ranging from collider to lepton flavour violating experiments. For a GeV mass heavy neutrino, the parameters related to dark matter production are constrained by the experimental results directly and can be further tested by future experiments such as SHiP
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