Furry picture transition rates in the intense fields at a lepton collider interaction point

The effect on particle physics processes by intense electromagnetic fields in the charge bunch collisions at future lepton colliders is considered. Since the charge bunch fields are tied to massive sources (the e+e− charges), a reference frame is chosen in which the fields appear to be co-propagating. Solutions of the Dirac equation minimally coupled to the electromagnetic fields reasonably associated with two intense overlapping charge bunches are obtained and found to be a Volkov solution with respect to a null 4-vector whose 3-vector part lies in the common propagation direction. These solutions are used within the Furry interaction picture to calculate the beamstrahlung transition rate for electron radiation due to interaction with the electromagnetic fields of two colliding charge bunches. New analytic expressions are obtained and compared numerically with the beamstrahlung in the electromagnetic field of one charge bunch. The techniques developed will be applied to other collider physics processes in due course

Soft theorems from conformal field theory

Strominger and collaborators recently proposed that soft theorems for gauge and gravity amplitudes can be interpreted as Ward identities of a 2d CFT at null infinity. In this paper, we will consider a specific realization of this CFT known as ambitwistor string theory, which describes 4d Yang-Mills and gravity with any amount of supersymmetry. Using 4d ambtwistor string theory, we derive soft theorems in the form of an infinite series in the soft momentum which are valid to subleading order in gauge theory and sub-subleading order in gravity. Furthermore, we describe how the algebra of soft limits can be encoded in the braiding of soft vertex operators on the worldsheet and point out a simple relation between soft gluon and soft graviton vertex operators which suggests an interesting connection to color-kinematics duality. Finally, by considering ambitwistor string theory on a genus one worldsheet, we compute the 1-loop correction to the subleading soft graviton theorem due to infrared divergences

Impact of heavy-flavour production cross sections measured by the LHCb experiment on parton distribution functions at low x

The impact of recent measurements of heavy-flavour production in deep inelastic ep scattering and in pp collisions on parton distribution functions is studied in a QCD analysis in the fixed-flavour number scheme at next-to-leading order. Differential cross sections of charm- and beauty-hadron production measured by LHCb are used together with inclusive and heavy-flavour production cross sections in deep inelastic scattering at HERA. The heavy-flavour data of the LHCb experiment impose additional constraints on the gluon and the sea-quark distributions at low partonic fractions x of the proton momentum, down to x∼5×10-6 . This kinematic range is currently not covered by other experimental data in perturbative QCD fits

Double-logarithms in Einstein-Hilbert gravity and supergravity

We study the interplay between graviton reggeization and double-logarithmic in energy contributions to four-graviton scattering in theories with and without supersymmetry. Predictions to all orders in the gravitational coupling are given for these double-logarithms. As the number of supersymmetries grows these terms generate a convergent behaviour for the amplitudes at very high energies. At two-loop level, we find agreement with previous exact results for N $$\mathcal{N}$$ = 8 supergravity and with those of Boucher-Veronneau and Dixon, who studied the N $$\mathcal{N}$$ = 4, 5, 6 supergravities using a conjectured double-copy structure of gravity

Resummations and non-perturbative corrections

We consider a generalization of the Borel resummation, which turns out to be equivalent to the standard Borel resummation. We apply it to the simplest large N duality between the pure Chern-Simons theory and the topological string on the resolved conifold, and obtain a simple integral formula for the free energy. Expanding this integral representation around the large radius point at finite string coupling g s , we find that it includes not only the M-theoretic resummation à la Gopakumar and Vafa, but also a non-perturbative correction in g s . Remarkably, the obtained non-perturbative correction is in perfect agreement with a proposal for membrane instanton corrections in arXiv:1306.1734 . Various other examples are also presented

Antideuterons from decaying gravitino dark matter

We study the possibility of improving the constraints on the lifetime of gravitino dark matter in scenarios with bilinear R-parity violation by estimating the amount of cosmic-ray antideuterons that can be produced in gravitino decays. Taking into account all different sources of theoretical uncertainties, we find that the margin of improvement beyond the limits already set by cosmic-ray antiproton data are quite narrow and unachievable for the next generation of experiments. However, we also identify more promising energy ranges for future experiments

Probing non-perturbative effects in M-theory

The AdS/CFT correspondence enables us to probe M-theory on various backgrounds from the corresponding dual gauge theories. Here we investigate in detail a three-dimensional U N N = 4 $$U(N)\mathcal{N}=4$$ super Yang-Mills theory coupled to one adjoint hypermultiplet and N f fundamental hypermultiplets, which is large N dual to M-theory on Ad S 4 × S 7 / ℤ N f $$Ad{S}_4\times {S}^7/{\mathrm{\mathbb{Z}}}_{N_f}$$ . Using the localization and the Fermi-gas formulation, we explore non-perturbative corrections to the partition function. As in the ABJM theory, we find that there exists a non-trivial pole cancellation mechanism, which guarantees the theory to be well-defined, between worldsheet instantons and membrane instantons for all rational (in particular, physical or integral) values of N f

Production of light stringy states

We discuss the direct production of light stringy states. Those states correspond to the lightest stringy excitations localized at the intersection of two D-brane stacks and their mass can be parametrically smaller than the string scale. Thus in a low string scale scenario one may observe stringy signatures at LHC even in the absence of the usual string resonances. We compute the tree level string scattering amplitude involving two gauge bosons and two such light stringy states. We give the squared amplitude summed over all polarization and gauge configuration and eventually apply the result to the quark sector of a D-brane realization of the Standard Model

Parton distribution functions at LO, NLO and NNLO with correlated uncertainties between orders

Sets of parton distribution functions (PDFs) of the proton are reported for the leading (LO), next-to-leading (NLO) and next-to-next-to-leading-order (NNLO) QCD calculations. The parton distribution functions are determined with the HERAFitter program using the data from the HERA experiments and preserving correlations between uncertainties for the LO, NLO and NNLO PDF sets. The sets are used to study cross-section ratios and their uncertainties when calculated at different orders in QCD. A reduction of the overall theoretical uncertainty is observed if correlations between the PDF sets are taken into account for the ratio of WW di-boson to Z boson production cross sections at the LHC

Conformal constraints for anomalous dimensions of leading-twist operators

Leading-twist operators have a remarkable property that their divergence vanishes in a free theory. Recently it was suggested that this property can be used for an alternative technique to calculate anomalous dimensions of leading-twist operators and allows one to gain one order in perturbation theory so that, i.e., two-loop anomalous dimensions can be calculated from one-loop Feynman diagrams, etc. In this work we study the feasibility of this program by a toy-model example of the φ3 theory in six dimensions. Our conclusion is that this approach is valid, although it does not seem to present considerable technical simplifications as compared to the standard technique. It does provide one, however, with a very nontrivial check of the calculation as the structure of the contributions is very different