We consider various configurations of T-branes which are non-abelian bound states of branes and were recently introduced by Cecotti, Cordova, Heckman and Vafa. They are a refinement of the concept of monodromic branes featured in phenomenological F-theory models. We are particularly interested in the T-branes corresponding to Z3 and Z4 monodromies, which are used to break E7 or E8 gauge groups to SU (5)GUT . Our results imply that the up-type and down-type Yukawa couplings for the breaking of E7 are zero, whereas up-type and down-type Yukawa couplings, together with right handed neutrino Yukawas are non-zero for the case of the breaking of E8. The dimension four proton decay mediating term is avoided in models with either E7 or E8 breaking.Recent studies have revealed that F-theory phenomenology can describe realistic features of particle phenomenology [1-3] (see also [4,5]). As compared to previous models for particle phenomenology involving D5 branes (type IIB) or D6 branes (type IIA), the F-theory approach localizes gauge fields on D7 branes wrapped on four cycles, matter on complex curves inside the four cycles and the Yukawa couplings at the intersection points of complex curves. The main observation of [1][2][3] was that all the fields are described in an eight-dimensional topological field theory giving rise to a four dimensional N = 1 supersymmetric field theory. The matter fields have Gaussian function on the directions normal to the matter curves so they are genuinely trapped on such curves. The F-theory trapping of matter curves can be nicely mapped into the matter curve restrictions appearing in heterotic strings [6].The formulation in terms of the eight-dimensional topological field theory has led to a series of important developments which uncovered various aspects of F-theory phenomenology (for recent reviews on the subject see [7-9]). One issue first pointed out in [10] was related to the existence of novel features like branch cuts in models giving rise to relevant Yukawa couplings. This was due to the fact that, when studying such theories, the adjoint field Φ describing the displacement orthogonal to the worldvolume of the D7 branes was fixed to a background value Φ taken to reside in the Cartan subalgebra. In order to achieve one heavy mass generation, a new concept needed to be introduced which is the seven brane monodromy. This means that, in order to deal with F-theory compactifications on a Calabi-Yau with generic complex structure, one needs to introduce branch cuts into the field theory and fields have to be twisted by Weyl reflections at the branch cuts. To get the Yukawa coupling in SU (5) GUT , one needs to consider the breaking E 6 → SU (5) which involves a field Φ with the above branch cuts.Very recently an important step has been taken towards a better understanding of this issue [11]. Instead of considering a diagonal Φ with branch cuts, the authors of [11] have considered a theory without branch cuts but with a non-diagonal Φ and denoted such non-diagonal case as seven-branes "T-...

We consider an SO(10) GUT model from F-theory compactified on an elliptically fibered Calabi-Yau with a D 5 singularity. To obtain the matter curves and the Yukawa couplings, we use a global description to resolve the singularity along the lines of [12]. We identify the vector and spinor matter representations and their Yukawa couplings and we explicitly build the G-fluxes in the global model and check the agreement with the semi-local results. As our bundle is of type SU(2k), some extra conditions need to be applied to match the fluxes, as observed in [19].

The role of niobium carbides in the localised corrosion initiation of 20Cr-25Ni-Nb advanced gas-cooled reactor fuel cladding. Corrosion Science, [108365].

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