arXiv subjects

Ye-Ling Zhou

Publications and source records attributed to Ye-Ling Zhou.

At least 37 records · Page 2Linked to original sources

arXiv2024

Gravitational waves from cosmic superstrings and gauge strings

We perform a phenomenological comparison of the gravitational wave (GW) spectrum expected from cosmic gauge string networks and superstring networks comprised of multiple string types. We show how violations of scaling behavior and the evolution of the number of relativistic degrees of freedom in the early Universe affect the GW spectrum. We derive simple analytical expressions for the GW spectrum from superstrings and gauge strings that are valid for all frequencies relevant to pulsar timing arrays (PTAs) and laser interferometers. We analyze the latest data from PTAs and show that superstring networks are consistent with 32 nHz data from NANOGrav, but are excluded by 3.2 nHz data at $3σ$ unless the string coupling $g_s<0.2$ or the strings evolve in only about 10% of the volume of the higher-dimensional space. We also point out that while gauge string networks are excluded by NANOGrav-15 data at $3σ$, they are completely compatible with EPTA and PPTA data. Finally, we study correlations between GW signals at PTAs and laser interferometers.

hep-ph↗

arXiv2024

Testing Realistic $SO(10)$ SUSY GUTs with Proton Decay and Gravitational Waves

We present a comprehensive analysis of a supersymmetric $SO(10)$ Grand Unified Theory, which is broken to the Standard Model via the breaking of two intermediate symmetries. The spontaneous breaking of the first intermediate symmetry, $B-L$, leads to the generation of cosmic strings and right-handed neutrino masses and further to an observable cosmological background of gravitational waves and generation of light neutrino masses via type-I seesaw mechanism. Supersymmetry breaking manifests as sparticle masses below the $B-L$ breaking but far above the electroweak scale due to proton decay limits. This naturally pushes the $B-L$ breaking scale close to the GUT scale, leading to the formation of metastable cosmic strings, which can provide a gravitational wave spectrum consistent with the recent Pulsar Timing Arrays observation. We perform a detailed analysis of this model using two-loop renormalisation group equations, including threshold corrections, to determine the symmetry-breaking scale consistent with the recent Pulsar Timing Arrays signals such as NANOGrav 15-year data and testable by the next-generation limits on proton decay from Hyper-K and JUNO. Simultaneously, we find the regions of the model parameter space that can predict the measured quark and lepton masses and mixing, baryon asymmetry of our Universe, a viable dark matter candidate and can be tested by a combination of neutrinoless double beta decay searches and limits on the sum of neutrinos masses.

hep-ph↗

arXiv2024

Revisiting Trimaximal TM2 mixing in two $A_4$ modular symmetries

We discuss a minimal lepton flavour model with two modular $A_4$ symmetries, one acting on neutrinos and the other acting on charged leptons. Two corresponding moduli fields are restricted at stabilisers. To avoid vanishing or degenerate lepton masses, the stabiliser in the charged lepton sector always preserves a $Z_3$ symmetry, and that in the neutrino preserves a $Z_2$ symmetry. By scanning all viable stabilisers, a unique Trimaximal TM2 mixing is predicted. However, the prediction of the lightest neutrino mass and the mass parameter in neutrinoless double beta decay, as well as two Majorana phases, are different and classified into three cases.

hep-ph↗

arXiv2024

Flipped SU(5): unification, proton decay, fermion masses and gravitational waves

We study supersymmetric (SUSY) flipped $SU(5)\times U(1)$ unification, focussing on its predictions for proton decay, fermion masses and gravitational waves. We performed a two-loop renormalisation group analysis and showed that the SUSY flipped $SU(5)$ model predicts a high GUT scale $M_{\rm GUT} > 10^{16}$ GeV. We also investigated the restrictions on the $M_{B-L}$ scale which is associated with the $U(1)_χ$ breaking scale. We found that the $M_{B-L}$ scale can vary in a broad region with negligible or little effect on the value of $M_{\rm GUT}$. Proton decay in this model is induced by dimension-6 operators only. The dimension-5 operator induced by SUSY contribution is suppressed due to the missing partner mechanism. We found that the partial decay width $p \to π^0 e^+$ is high suppressed, being at least one order of magnitude lower than the future Hyper-K sensitivity. We also studied fermion (including neutrino) masses and mixings which can also influence proton decay. We presented two scenarios of flavour textures to check the consistency of the results with fermion masses and mixing. The $B-L$ gauge breaking leads to the generation of cosmic strings. The $B-L$ scale here is not constrained by gauge coupling unification. If this scale is very close that of GUT breaking, strings can be unstable due to the decay to monopole-antimonople pair. Such metastable strings can be used to explain the NANOGrav signals of stochastic gravitational wave background, which may be interpreted here as resulting from the decay of metastable cosmic strings.

hep-ph↗

arXiv2023

A Predictive and Testable Unified Theory of Fermion Masses, Mixing and Leptogenesis

We consider a minimal non-supersymmetric $SO(10)$ Grand Unified Theory (GUT) model that can reproduce the observed fermionic masses and mixing parameters of the Standard Model. We calculate the scales of spontaneous symmetry breaking from the GUT to the Standard Model gauge group using two-loop renormalisation group equations. This procedure determines the proton decay rate and the scale of $U(1)_{B-L}$ breaking, which generates cosmic strings and the right-handed neutrino mass scales. Consequently, the regions of parameter space where thermal leptogenesis is viable are identified and correlated with the fermion masses and mixing, the neutrinoless double beta decay rate, the proton decay rate, and the gravitational wave signal resulting from the network of cosmic strings. We demonstrate that this framework, which can explain the Standard Model fermion masses and mixing and the observed baryon asymmetry, will be highly constrained by the next generation of gravitational wave detectors and neutrino oscillation experiments which will also constrain the proton lifetime.

hep-ph↗

arXiv2022

Classification of Abelian domain walls

We discuss domain walls from spontaneous breaking of Abelian discrete symmetries $Z_N$. A series of different domain wall structures are predicted, depending on the symmetry and charge assignments of scalars leading to the spontaneous symmetry breaking (SSB). A widely-existing type of domain walls are those separating degenerate vacua which are adjacent in the field space. We denote these walls as adjacency walls. In the case that $Z_N$ terms are small compared with the $U(1)$ terms, the SSB of $U(1)$ generates strings first and then adjacency walls bounded by strings are generated after the SSB of $Z_N$. For symmetries larger than $Z_3$, non-adjacent vacua exist, we regard walls separating them as non-adjacency walls. These walls are unstable if $U(1)$ is a good approximation. If the discrete symmetry is broken via multiple steps, we arrive at a complex structure that one kind of walls wrapped by another type. On the other hand, if the symmetry is broken in different directions independently, walls generated from the different breaking chains are blind to each other.

hep-ph↗

arXiv2022

Collapsing domain walls beyond $Z_2$

Discrete symmetries are widely imposed in particle theories. It is well-known that the spontaneous breaking of discrete symmetries leads to domain walls. Current studies of domain walls have focused on those from the spontaneous breaking of a $Z_2$ symmetry. Larger discrete symmetries have multiple degenerate vacua, leading to the domain walls in principle different from the simplest $Z_2$ domain wall. We take domain walls from $Z_N$ symmetry breaking as an illustrative study, and study in detail the $Z_3$ case, in which semi-analytical results for the tension and thickness of domain walls are derived. Explicit symmetry breaking terms lead to the dynamics of domain walls collapsing more complicated than the $Z_2$ case. Gravitational wave signals deviate from those from $Z_2$ domain walls.

hep-ph↗

arXiv2021

Flipped SU(5) with modular $A_4$ symmetry

We study Flipped $SU(5)\times U(1)$ Grand Unified Theories (GUTs) with $Γ_3\simeq A_4$ modular symmetry. We propose two models with different modular weights assignments, where the fermion mass hierarchy can arise from weighton fields. In order to relax the constraint on the Dirac neutrino Yukawa matrix we appeal to mechanisms which allow incomplete GUT representations, allowing a good fit to quark and charged lepton masses and quark mixing for a single modulus field $τ$, with the neutrino masses and lepton mixing well determined by the type I seesaw mechanism, at the expense of some tuning. We also discuss the double seesaw possibility allowed by the extra singlets generically predicted in such string inspired theories.

hep-ph↗

arXiv2021

Confronting SO(10) GUTs with proton decay and gravitational waves

Grand Unified Theories (GUT) predict proton decay as well as the formation of cosmic strings which can generate gravitational waves. We determine which non-supersymmetric $SO(10)$ breaking chains provide gauge unification in addition to a gravitational signal from cosmic string decay. We calculate the GUT and intermediate scales for these $SO(10)$ breaking chains by solving the renormalisation group equations at the two-loop level. This analysis predicts the GUT scale, hence the proton lifetime, in addition to the scale of cosmic string generation and thus the associated gravitational wave signal. We determine which $SO(10)$ breaking chains survive in the event of the null results of the next generation of gravitational waves and proton decay searches and determine the correlations between proton decay and gravitational waves scales if these observables are measured.

hep-ph↗

arXiv2021

Gravitational waves from first-order phase transitions in Majoron models of neutrino mass

We show how the generation of right-handed neutrino masses in Majoron models may be associated with a first-order phase transition and accompanied by the production of a stochastic background of gravitational waves (GWs). We explore different energy scales with only renormalizable operators in the effective potential. If the phase transition occurs above the electroweak scale, the signal can be tested by future interferometers. We consider two possible energy scales for phase transitions below the electroweak scale. If the phase transition occurs at a GeV, the signal can be tested at LISA and provide a complementary cosmological probe to right-handed neutrino searches at the FASER detector. If the phase transition occurs below 100 keV, we find that the peak of the GW spectrum is two or more orders of magnitude below the putative NANOGrav GW signal at low frequencies, but well within reach of the SKA and THEIA experiments. We show how searches of very low frequency GWs are motivated by solutions to the Hubble tension in which ordinary neutrinos interact with the dark sector. We also present general calculations of the phase transition temperature and Euclidean action that apply beyond Majoron models.

hep-ph↗

arXiv2021

Light neutrino masses from gravitational condensation: the Schwinger-Dyson approach

In this work we demonstrate that non-zero neutrino masses can be generated from gravitational interactions. We solve the Schwinger-Dyson equations to find a non-trivial vacuum thereby determining the scale of the neutrino condensate and the number of new particle degrees of freedom required for gravitationally induced dynamical chiral symmetry breaking. We show for minimal beyond the Standard Model particle content, the scale of the condensation occurs close to the Planck scale.

hep-ph↗

arXiv2021

Twin Modular $S_4$ with $SU(5)$ GUT

We discuss the $SU(5)$ grand unified extension of flavour models with multiple modular symmetries. The proposed model involves two modular $S_4$ groups, one acting in the charged fermion sector, associated with a modulus field value $τ_T$ with residual $Z_3^T$ symmetry, and one acting in the right-handed neutrino sector, associated with another modulus field value $τ_{SU}$ with residual $Z_2^{SU}$ symmetry. Quark and lepton mass hierarchies are naturally generated with the help of weightons, which are SM singlet fields, where their non-zero modular weights play the role of Froggatt-Nielsen charges. The model predicts TM$_1$ lepton mixing, and neutrinoless double beta decay at rates close to the sensitivity of current and future experiments, for both normal and inverted orderings, with suppressed corrections from charged lepton mixing due to the triangular form of its Yukawa matrix.

hep-ph↗

arXiv2021

Gravitational wave signatures from discrete flavor symmetries

Non-Abelian discrete symmetries have been widely used to explain the patterns of lepton masses and flavor mixing. In these models, a given symmetry is assumed at a high scale and then is spontaneously broken by scalars (the flavons), which acquire vacuum expectation values. Typically, the resulting leading order predictions for the oscillation parameters require corrections in order to comply with neutrino oscillation data. We introduce such corrections through an explicit small breaking of the symmetry. This has the advantage of solving the cosmological problems of these models without resorting to inflation. The explicit breaking induces an energy difference or "bias" between different vacua and drives the evolution of the domain walls, unavoidably produced after the symmetry breaking, towards their annihilation. Importantly, the wall annihilation leads to gravitational waves which may be observed in current and/or future experiments. We show that a distinctive pattern of gravitational waves with multiple overlapped peaks is generated when walls annihilate, which is within the reach of future detectors. We also show that cosmic walls from discrete flavor symmetries can be cosmologically safe for any spontaneous breaking scale between 1 and $10^{18}$ GeV, if the bias is chosen adequately, without the need to inflate the walls away. We use as an example a particular $A_4$ model in which an explicit breaking is included in right-handed neutrino mass terms.

hep-ph↗

arXiv2021

Gravitational waves and proton decay: complementary windows into GUTs

Proton decay is a smoking gun signature of Grand Unified Theories (GUTs). Searches by Super-Kamiokande have resulted in stringent limits on the GUT symmetry breaking scale. The large-scale multipurpose neutrino experiments DUNE, Hyper-Kamiokande and JUNO will either discover proton decay or further push the symmetry breaking scale above $10^{16}$ GeV. Another possible observational consequence of GUTs is the formation of a cosmic string network produced during the breaking of the GUT to the Standard Model gauge group. The evolution of such a string network in the expanding Universe produces a stochastic background of gravitational waves which will be tested by a number of gravitational wave detectors over a wide frequency range. We demonstrate the non-trivial complementarity between the observation of proton decay and gravitational waves produced from cosmic strings in determining $SO(10)$ GUT breaking chains. We show that such observations could exclude $SO(10)$ breaking via flipped $SU(5)\times U(1)$ or standard $SU(5)$, while breaking via a Pati-Salam intermediate symmetry, or standard $SU(5)\times U(1)$, may be favoured if a large separation of energy scales associated with proton decay and cosmic strings is indicated. We note that recent results by the NANOGrav experiment have been interpreted as evidence for cosmic strings at a scale $\sim 10^{14}$ GeV. This would strongly point towards the existence of GUTs, with $SO(10)$ being the prime candidate. We show that the combination with already available constraints from proton decay allows to identify preferred symmetry breaking routes to the Standard Model.

hep-ph↗

arXiv2020

CP violation in neutral lepton transition dipole moment

The $CP$ violation in the neutrino transition electromagnetic dipole moment is discussed in the context of the Standard Model with an arbitrary number of right-handed singlet neutrinos. A full one-loop calculation of the neutrino electromagnetic form factors is performed in the Feynman gauge. A non-zero $CP$ asymmetry is generated by a required threshold condition for the neutrino masses along with non-vanishing $CP$ violating phases in the lepton flavour mixing matrix. We follow the paradiagm of $CP$ violation in neutrino oscillations to parametrise the flavour mixing contribution into a series of Jarlskog-like parameters. This formalism is then applied to a minimal seesaw model with two heavy right-handed neutrinos denoted $N_1$ and $N_2$. We observe that the $CP$ asymmetries for decays into light neutrinos $N\to νγ$ are extremely suppressed, maximally around $10^{-17}$. However the $CP$ asymmetry for $N_2 \to N_1 γ$ can reach of order unity. Even if the Dirac $CP$ phase $δ$ is the only source of $CP$ violation, a large $CP$ asymmetry around $10^{-5}$-$10^{-3}$ is comfortably achieved.

hep-ph↗

arXiv2020

Symmetries and stabilisers in modular invariant flavour models

The idea of modular invariance provides a novel explanation of flavour mixing. Within the context of finite modular symmetries $Γ_N$ and for a given element $γ\in Γ_N$, we present an algorithm for finding stabilisers (specific values for moduli fields $τ_γ$ which remain unchanged under the action associated to $γ$). We then employ this algorithm to find all stabilisers for each element of finite modular groups for $N=2$ to $5$, namely, $Γ_2\simeq S_3$, $Γ_3\simeq A_4$, $Γ_4\simeq S_4$ and $Γ_5\simeq A_5$. These stabilisers then leave preserved a specific cyclic subgroup of $Γ_N$. This is of interest to build models of fermionic mixing where each fermionic sector preserves a separate residual symmetry.

hep-ph↗

arXiv2020

Gravitational waves from neutrino mass and dark matter genesis

We introduce a model in which the genesis of dark matter (DM) and neutrino masses is associated with a first order phase transition of a scalar singlet field. During the phase transition a source right-handed neutrino (RHN) acquires a spacetime-dependent mass dynamically, a small fraction of which is converted via resonant oscillations into a very weakly mixed dark RHN which decays to a dark matter RHN with the observed relic abundance. Neutrino masses are generated via a traditional two RHN type-I seesaw between a fourth RHN and the source neutrino. The gravitational waves produced during the phase transition have a peak frequency that increases with the DM mass, and are detectable at future gravitational wave interferometers for DM masses above ~ 1 MeV. Since the source RHNs are heavier than the electroweak scale, successful leptogenesis is also attainable.

hep-ph↗

arXiv2020

Nonstandard neutrino interactions and mu-tau reflection symmetry

Nonstandard interactions (NSIs), possible subleading effects originating from new physics beyond the Standard Model, may affect the propagation of neutrinos and eventually contribute to measurements of neutrino oscillations. Besides this, $ μ-τ$ reflection symmetry, naturally predicted by non-Abelian discrete flavor symmetries, has been very successful in explaining the observed leptonic mixing patterns. In this work, we study the combined effect of both. We present an $S_4$ flavor model with $μ-τ$ reflection symmetry realized in both neutrino masses and NSIs. Under this formalism, we perform a detailed study for the upcoming neutrino experiments DUNE and T2HK. Our simulation results show that under the $μ-τ$ reflection symmetry, NSI parameters are further constrained and the mass ordering sensitivity is less affected by the presence of NSIs.

hep-ph↗