On the soft limit of open string disk amplitudes with massive states

We discuss the soft behaviour of open string amplitudes with gluons and massive states in any dimension. Notwithstanding non-minimal couplings of massive higher spin states to gluons, relying on OPE and factorization, we argue that the leading and subleading terms are universal and identical to the ones in Yang-Mills theories. In order to illustrate this, we compute some 4-point amplitudes on the disk involving gluons, massive states and, for the bosonic string, tachyons. For the superstring, we revisit the structure of the massive super-multiplets at the first massive level and rewrite the amplitudes in D = 4 in the spinor helicity formalism, that we adapt to accommodate massive higher spin states. We also check the validity of a recently obtained formula relating open superstring amplitudes for mass-less states at tree-level to SYM amplitudes, by factorisation on two-particle massive poles. Finally we analyse the holomorphic soft limit of superstring amplitudes with one massive insertion

Unoriented quivers with flavour

We discuss unoriented quivers with flavour that arise from D3-branes at local orbifold singularities, in the presence of Ω-planes and non-compact D7-branes. We produce a wide class of unoriented quiver gauge theories, including new instances of $\mathcal{N}$ = 1 superconformal theories. We then consider unoriented D-brane instanton corrections of both ‘gauge’ and ‘exotic’ kinds. In particular, we show that conformal symmetry can be dynamically broken via the generation of exotic superpotentials. Finally we discuss aspects of the recently proposed $\mathcal{N}$ = 1 remnant of $\mathcal{N}$ = 4 S-duality. We identify new candidate dual pairs for the $\mathbb{C}$ 3 / $\mathbb{Z}$ n series of unoriented quiver gauge theories with n odd

Testing General Relativistic Predictions with the LAGEOS Satellites

The spacetime around Earth is a good environment in order to perform tests of gravitational theories. According to Einstein’s view of gravitational phenomena, the Earth mass-energy content curves the surrounding spacetime in a peculiar way. This (relatively) quiet dynamical environment enables a good reconstruction of geodetic satellites (test masses) orbit, provided that high-quality tracking data are available. This is the case of the LAGEOS satellites, built and launched mainly for geodetic and geodynamical purposes, but equally good for fundamental physics studies. A review of these studies is presented, focusing on data, models, and analysis strategies. Some recent and less recent results are presented. All of them indicate general relativity theory as a very good description of gravitational phenomena, at least in the studied environment

Neutron Majorana mass from exotic instantons

We show how a Majorana mass for the neutron could result from non-perturbative quantum gravity effects peculiar to string theory. In particular, “exotic instantons” in un-oriented string compactifications with D-branes extending the (supersymmetric) standard model could indirectly produce an effective operator δm n t n + h . c . . In a specific model with an extra vector-like pair of ‘quarks’, acquiring a large mass proportional to the string mass scale (exponentially suppressed by a function of the string moduli fields), δm can turn out to be as low as 10 −24 -10 −25 eV

Un-oriented quiver theories for Majorana neutrons

In the context of un-oriented open string theories, we identify quivers whereby a Majorana mass for the neutron is indirectly generated by exotic instantons. We discuss two classes of (Susy) Standard Model like quivers, depending on the embedding of SU(2) W in the Chan-Paton group. In both cases, the main mechanism involves a vector-like pair mixing through a non-perturbative mass term. We also discuss possible relations between the phenomenology of Neutron-Antineutron oscillations and LHC physics in these models. In particular, a vector-like pair of color-triplet scalars or color-triplet fermions could be directly detected at LHC, compatibly with n − n ¯ $$n-\overline{n}$$ limits. Finally we briefly comment on Pati-Salam extensions of our models

Neutron Majorana mass from exotic instantons in a Pati-Salam model

We show how exotic stringy instantons can generate an effective interaction between color diquark sextets in a Pati-Salam model, inducing a Majorana mass term for the neutron. In particular, we discuss a simple quiver theory for a Pati-Salam like model, as an example in which the calculations of exotic instanton effects are simple and controllable. We discuss some different possibilities in order to generate n − n ¯ $$n-\overline{n}$$ oscillations testable in the next generation of experiments, Majorana mass matrices for neutrini and a Post-Sphaleron Baryogenesis scenario. Connections with Dark Matter issues and the Higgs mass Hierarchy problem are discussed, in view of implications for LHC and rare processes physics. The model may be viewed as a completion of a Left-Right symmetric extension of the Standard Model, alternative to a GUT-inspired scenario. Combined measures in Neutron-Antineutron physics, FCNC, LHC, Dark Matter could rule out the proposed model or uncover aspects of physics at the Planck scale

Probing the nature of Zc(′) states via the ηcρ decay

The nature of the so-called XYZ states is a long-standing problem. It has been suggested that such particles may be described as compact four-quark states or loosely bound meson molecules. In the present work we analyze the Zc(′)→ηcρ decay using both approaches. Such channel might provide useful insights on the nature of the Zc(′) , helping discriminating between the two different models

M-theory compactifications to three dimensions with M2-brane potentials

We study a class of compactifications of M-theory to three dimensions that preserve N = 2 supersymmetry and which have the defining feature that a probe space-time filling M2 brane feels a non-trivial potential on the internal manifold. Using M-theory/F-theory duality such compactifications include the uplifts of 4-dimensional N = 1 type IIB compactifications with D3 potentials to strong coupling. We study the most general 8-dimensional manifolds supporting these properties, derive the most general flux that induces an M2 potential, and show that it is parameterised in terms of two real vectors. We study the supersymmetry equations when only this flux is present and show that over the locus where the M2 potential is non-vanishing the background takes the form of a Calabi-Yau three-fold fibered over a 2-dimensional base spanned by the flux vectors, while at the minima of the potential the flux vanishes. Allowing also for non-vanishing four-form flux with one leg in the internal directions we find that the Calabi-Yau three-fold in the fibration is replaced by an SU(3)-structure manifold with torsion classes satisfying 2 W 4 = − W 5

Double soft theorems in gauge and string theories

We investigate the tree-level S-matrix in gauge theories and open superstring theory with several soft particles. We show that scattering amplitudes with two or three soft gluons of non-identical helicities behave universally in the limit, with multi-soft factors which are not the product of individual soft gluon factors. The results are obtained from the BCFW recursion relations in four dimensions, and further extended to arbitrary dimensions using the CHY formula. We also find new soft theorems for double soft limits of scalars and fermions in N = 4 $$\mathcal{N}=4$$ and pure N = 2 $$\mathcal{N}=2$$ SYM. Finally, we show that the double-soft-scalar theorems can be extended to open superstring theory without receiving any α ′ corrections

Exact coefficients for higher dimensional operators with sixteen supersymmetries

We consider constraints on higher-dimensional operators for supersymmetric effective field theories. In four dimensions with maximal supersymmetry and SU(4) R-symmetry, we demonstrate that the coefficients of abelian operators F n with MHV helicity configurations must satisfy a recursion relation, and are completely determined by that of F 4 . As the F 4 coefficient is known to be one-loop exact, this allows us to derive exact coefficients for all such operators. We also argue that the results are consistent with the SL(2,Z) duality symmetry. Breaking SU(4) to Sp(4), in anticipation for the Coulomb branch effective action, we again find an infinite class of operators whose coefficients are determined exactly. We also consider three-dimensional N $$\mathcal{N}$$ = 8 as well as six-dimensional N $$\mathcal{N}$$ = (2 , 0) , (1 , 0) and (1 , 1) theories. In all cases, we demonstrate that the coefficient of dimension-six operator must be proportional to the square of that of dimension-four