[en] We analyse the non-perturbative superpotential due to M5-brane instantons in F-theory compactifications on Calabi–Yau fourfolds. The M5 partition function is obtained via holomorphic factorisation by explicitly performing the sum over chiral 3-form fluxes. Comparison with the partition function of fluxed Euclidean D3-brane instantons in Type IIB orientifolds allows us to fix the spin structure on the intermediate Jacobian of the M5-instanton. We furthermore analyse the contribution of the M5-instanton to the superpotential in the presence of G₄ gauge flux, where the superpotential is dressed with matter fields. We explicitly evaluate the pullback of G₄ onto the M5-brane as a measure for the presence of charged instanton zero modes. This accounts for the M5 charge both under massless U(1)s, if present, and under what corresponds in Type II language to geometrically massive U(1)s.

[en] We construct non-relativistic string and p-brane actions in Newton-Cartan background using the limiting procedure from the relativistic string and p-brane action in general background. We also find their Hamiltonian formulations when however we restrict ourselves to the case of the vanishing gauge field m_μ. (orig.)

[en] In this work we compute relative periods for B-branes, realized in terms of divisors in a compact Calabi-Yau hypersurface, by means of direct integration. Although we exemplify the method of direct integration with a particular Calabi-Yau geometry, the recipe automatically generalizes for divisors in other Calabi-Yau geometries as well. From the calculated relative periods we extract double-logarithmic periods. These periods qualify to describe disk instanton generated N=1 superpotentials of the corresponding compact mirror Calabi-Yau geometry in the large volume regime. Finally we extract the integer invariants encoded in these brane superpotentials.

[en] We carry out nonrelativistic expansion for NS5 brane based on a codimension two foliation of type IIA supergravity background. We simultaneously expand the world-volume fields in an appropriate 1/c${}^2$ expansion together with the background fluxes. When put together, the resulting procedure yields a finite world-volume action for nonrelativistic NS5 brane that is coupled to String Newton-Cartan background.

[en] We started a program to study the open string integrality invariants (LMOV invariants) for toric Calabi-Yau 3-folds with Aganagic-Vafa brane (AV-brane) several years ago. This paper is devoted to the case of resolved conifold with one out AV-brane in any integer framing τ , which is the large N duality of Chern-Simons theory for a framed unknot with integer framing τ in S³. By using the methods from string dualities, we compute several explicit formulae of the corresponding LMOV invariants for this special model, whose integrality properties have been proved in a separated paper [56].

[en] We study pulsating strings both on a single stack of NS5-branes and two orthogonal stacks of NS5-branes (the so called I-brane) by using the Polyakov form of the fundamental string action. For the I-brane background, by using a symmetry that decouples the two spheres from the flat geometry, we study pulsating solutions of the string when it pulsates on both the spheres independently and simultaneously. We finally derive the energy of pulsating strings as a function of adiabatic invariant oscillation number in these cases and studied some limiting cases in detail.

[en] In this paper, we present double dimensional reduction of the complete M5-brane action in the Sen formalism of self-dual form. Although in this formalism the gravity couples to the independent pseudo-2-form and pseudo-3-form fields in a non-standard and very complicated way, the double dimensional reduction on the complete action can be carried out. This is by dualising some components of the pseudo-2-form field and integrating out the pseudo-3-form field. We show explicitly that the double dimensional reduction on a circle gives rise to the complete D4-brane or the complete dual D4-brane action depending on what components of the pseudo-2-form field are dualised. The duality between the D4-brane and dual D4-brane actions are realised in the viewpoint of the Sen formalism as the swapping of the roles of the components of the pseudo-2-form field between those which are dualised and those which remain. We also make a brief outline on how to generalise this to the cases of dimensional reduction on some other spaces as well as how to understand the duality of reduced action from the viewpoint of the Sen formalism. An explicit example for dimensional reduction of the quadratic six-dimensional action on a torus is given and the realisation of its S-duality is also discussed.

[en] We investigate a novel mechanism of dynamical tuning of a flat potential in the open string landscape within the context of warped brane-antibrane inflation in type IIB string theory. Because of competing effects between interactions with the moduli stabilizing D7-branes in the warped throat and anti-D3-branes at the tip, a stack of branes gives rise to a local minimum of the potential, holding the branes high up in the throat. As branes successively tunnel out of the local minimum to the bottom of the throat the potential barrier becomes lower and is eventually replaced by a flat inflection point, around which the remaining branes easily inflate. This dynamical flattening of the inflaton potential reduces the need to fine tune the potential by hand, and also leads to successful inflation for a larger range of inflaton initial conditions, due to trapping in the local minimum.

[en] We study the bounds on tensor wave in a class of twisted inflation models, where D(4+2k)-branes are wrapped on cycles in the compact manifold and wrap the Kaluza-Klein direction in the corresponding effective field theory. While the lower bound is found to be analogous to that in type IIB models of brane inflation, the upper bound turns out to be significantly different. This is argued for a range of values for the parameter g_sM satisfying the self-consistency relation and the WMAP data. Further, we observe that the wrapped D8-brane appears to be the most attractive from a cosmological perspective.

[en] Recently, Padmanabhan discussed that the difference between the number of degrees of freedom on the boundary surface and the number of degrees of freedom in a bulk region causes the accelerated expansion of the universe. The main question arising is: what is the origin of this inequality between the surface degrees of freedom and the bulk degrees of freedom? We answer this question in M-theory. In our model, first M0-branes are compactified on one circle and ND0-branes are created. Then ND0-branes join each other, grow, and form one D5-branes. Next, the D5-brane is compactified on two circles and our universe’s D3-brane, two D1-branes and some extra energies are produced. After that, one of the D1-branes, which is closer to the universe’s brane, gives its energy into it, and this leads to an increase in the difference between the numbers of degrees of freedom and the occurring inflation era. With the disappearance of this D1-brane, the number of degrees of freedom of boundary surface and bulk region become equal and inflation ends. At this stage, extra energies that are produced due to the compactification cause an expansion of the universe and deceleration epoch. Finally, another D1-brane dissolves in our universe’s brane, leads to an inequality between degrees of freedom, and there occurs a new phase of acceleration