This talk focuses on the construction of F-theory GUTs and their low energy implications. Alternative mechanisms of symmetry breaking will be described in prototype examples. Some phenomenological issues, including the computation of Yukawa couplings and the origin of discrete symmetries in this framework will be discussed.

Renormalisable supersymmetric grand unified theories typically

employ large representations which lead to a perturbative Landau pole at energies soon above the unification scale. The UV limit may still make sense if the theory approaches a nonperturbative fixed point there. Although the RG flow cannot be followed, one can check various constraints which a consistent fixed point must satisfy....

We discuss a common origin of four-dimensional flavor and CP symmetries in the context of heterotic string theory with standard embedding. We find that the flavor symmetries of fundamental and anti-fundamental representations of $E_6$ gauge group are governed by geometric symmetries of Calabi-Yau threefolds, i.e., the symplectic modular symmetry. Furthermore, the CP symmetry is identified with...

We describe the orgins of Standard Model quark/lepton masses and the CKM mixing pattern in an SU(8) theory through a set of d=5 operators induced by the gravitational effect.

Grand Unified Theories (GUTs) generically predict direct transition processes between quarks and leptons, and searching for proton decay is one of the unique ways to directly test GUTs. For most of the proton (and neutron) decay modes, the current lifetime limits are set by the Super-Kamiokande (Super-K) experiment, whose detector is the world’s largest underground water Cherenkov detector....

I will discuss the possibility that a heavy, metastable, dark right-handed neutrino with mass in the TeV-PeV range can play the role of (cold) dark matter particle. The right abundance would be produced by the Higgs induced mixing with a seesaw right-handed neutrino (RHINO model), i.e., by sterile-sterile neutrino mixing. Such a mixing would necessarily require a further extension of the...

There is increasing evidence suggesting a discrepancy between the cosmic dipole observed in the number count of distant galaxies and the one derived from the cosmic microwave background (CMB). In this study, we investigate the possibility that the cosmic dipole problem can be addressed by considering the QCD axion, a hypothetical particle that arises from the spontaneous breaking of the...

Asymmetric dark matter is one of alternative framework of dark matter to the weakly interacting massive particle framework, where its relic abundance is determined by the particle-antiparticle asymmetry. Once the dark matter asymmetry is originated from the same mechanism as the baryon asymmetry, the dark matter mass is predicted to be of GeV. Compositeness of asymmetric dark matter plays...

We investigate the first-order phase transition catalyzed by primordial black holes~(PBHs) in the early Universe. We find that super-horizon curvature perturbations generated in this scenario lead to the production of gravitational waves when the scalar modes re-enter the horizon. If PBHs with masses about $10^{-13}M_{\odot}$ constitute all dark matter, the first-order electroweak phase...

I will discuss how proton decay, combined with gravitational waves, can be used to test Grand Unified Theories (GUTs). In particular, proton decay searches by large multipurpose neutrino experiments such as 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...

In this talk, I will discuss the decay of metastable cosmic strings. By moving beyond the conventional thin string approximation, we explore the dynamics of cosmic strings with finite sizes, addressing a critical gap in previous estimates. This approach yields a more reliable lower limit on the tunneling rate, challenging earlier assumptions. The significance of these findings is underscored...

I will talk about the gravitational waves that can be produced from early universe symmetry breakings such as phase transitions and cosmic strings, which can help

reveal more information GUT and others. The focus is partially on theory development and partially on experimental status.

Flavor symmetry and grand unified symmetry are powerful tools to address the flavor structure of quarks and leptons. It is appealing to combine flavor symmetry with grand unification theories. In modular flavor symmetry, the flavons are replaced by modular forms and thus the resulting models are very economic and predictive. In this talk, I shall discuss the grand unification theories with...

Given the tremendous phenomenological success of the Standard Model (SM) framework, it becomes increasingly important to understand to what extent its specific structure dynamically emerges from unification principles. In this talk, I will discuss an anomaly-free supersymmetric (SUSY) Grand Unification model based upon gauge trinification SU(3)^3 symmetry and a local SU(2) x U(1) family...

In the precision frontier, effective field theories have been widely used to describe the new physics effects in a model independent way. It is intriguing to find ultraviolate (UV) theories that generate certain effective operators in the low energy regime, but the traditional way of integrating out heavy fields requires individual studies of UV models, which can be at odds with the bottom-up...

We build a SU(5) model with type-I+III seesaw by introducing a fermion field ${\bf 24}_F$. Under the condition of gauge coupling unification at two-loop level, we scan the parameter space of new particles. We find $M_{\Sigma}$ should be light to increase the scale of $M_{\rm GUT}$. Three new particles satisfy the following mass hierarchy $M_{\Sigma}

Gravitational waves can be produced from first order cosmological phase transitions that occur early in the Universe. I will show exciting recent results showing that i) some scenarios with grand unification may already be constrained by LIGO data because they imply a first order phase transition that is too strong and ii) a possible signal of a stochastic gravitational wave background from...

I will discuss a novel solution to the strong CP problem based on modular invariance. The latter is inherent to toroidal compactifications in string theory. We show that anomaly-free modular symmetry allows for simple effective theories of flavour and CP where (i) the QCD $\theta$-angle vanishes, (ii) the CKM phase is large, (iii) quark and lepton masses and mixings can be reproduced up to...

It is well known that the minimal renormalizable SU(5) grand unified theory is ruled out: it predicts same masses of down quarks and charged leptons, the gauge couplings do not unify and neutrinos are massless. We show here that all this can be cured simultaneously by the addition of higher-dimensional effective operators. However, the theory lives on the edge since the unification scale turns...