We recompute the recently derived two-loop five-point all-plus Yang-Mills amplitude using unitarity and recursion. Recursion requires augmented recursion to determine the subleading pole. Using these methods, the simplicity of this amplitude is understood.

The nonlinear Breit-Wheeler process is studied in the presence of strong and short laser pulses. We show that for a relativistically intense plane-wave laser field many features of the momentum distribution of the produced electron-positron pair like its extension, region of highest probability and carrier-envelope phase effects can be explained from the classical evolution of the created particles in the background field. To this end an intuitive semiclassical picture based on the local constant-crossed field approximation applied on the probability-amplitude level is established and compared with the standard approach used in QED-PIC codes. The main difference is the substructure of the spectrum, which results from interference effects between macroscopically separated formation regions. In order to compare the predictions of the semiclassical approach with exact calculations, a very fast numerical scheme is introduced. It renders the calculation of the fully differential spectrum on a grid which resolves all interference fringes feasible. Finally, the difference between classical and quantum absorption of laser four-momentum in the process is pointed out and the dominance of the former is proven. As a self-consistent treatment of the quantum absorption is not feasible within existing QED-PIC approaches, our results provide reliable error estimates relevant for regimes where the laser depletion due to a developing QED cascade becomes significant.

Motivated by both concepts of Adler’s recent work on utilizing Clifford algebra as the linear line element $ds=⟨{\gamma }_{\mu }⟩d{X}^{\mu }$ and the fermionization of the cylindrical worldsheet Polyakov action, we introduce a new type of spacetime quantization that is fully covariant. The theory is based on the reinterpretation of Adler’s linear line element as $ds={\gamma }_{\mu }⟨\lambda {\gamma }^{\mu }⟩$, where $\lambda$ is the characteristic length of the theory. We name this new operator the “spacetime interval operator” and argue that it can be regarded as a natural extension to the one-forms in the $U(\mathfrak{s}u(2))$ noncommutative geometry. By treating Fourier momentum as the particle momentum, the generalized uncertainty principle of the $U(\mathfrak{s}u(2))$ noncommutative geometry, as an approximation to the generalized uncertainty principle of our theory, is derived and is shown to have a lowest order correction term of the order $p^2$ similar to that of Snyder’s. The holography nature of the theory is demonstrated and the predicted fuzziness of the geodesic is shown to be much smaller than conceivable astrophysical bounds.

We point out a potential common origin of the recently observed 750 GeV diphoton resonance and a weakly interacting massive particle (WIMP) candidate. In a dark QCD sector with an unbroken dark $G$ parity, the diphoton resonance could be a dark $G$-even pion, while the WIMP could be the lightest dark $G$-odd pion. Both particles are Standard Model gauge singlets and have the same decay constant. For the dark pion decay constant of around 500 GeV, both the diphoton excess at the LHC and the dark matter thermal abundance can be accommodated in our model. Our model predicts additional dark $G$-even and dark $G$-odd color-octet pions within reach of the 13 TeV LHC runs. For the $5+\overline{5}$ model, compatible with the grand unified theories, the WIMP mass is predicted to be within (613,750) GeV.

We study lepton flavor violating hadron decays of the tau lepton within the simplest little Higgs model. Namely we consider $\tau \to \mu (P,V,PP)$ where $P$ and $V$ are short for a pseudoscalar and a vector meson. We find that, in the most positive scenarios, branching ratios for these processes are predicted to be, at least, four orders of magnitude smaller than present experimental bounds.

In this paper we continue our program to construct a model for high energy soft interactions, based on the CGC/saturation approach. We demonstrate that in our model, which describes diffractive physics as well as multiparticle production at high energy, the density variation mechanism leads to the value of $v_2$, which is about 60%–70% of the measured $v_2$. Bearing in mind that in the CGC/saturation approach there are two other mechanisms present, Bose enhancement in the wave function and local anisotropy, we believe that the azimuthal long range rapidity correlations in proton-proton collisions stem from the CGC/saturation physics, and not from quark-gluon plasma production.

A simple variant of a realistic flavor symmetry scheme for fermion masses and mixings provides a possible interpretation of the diphoton anomaly as an electroweak singlet “flavon.” The existence of TeV scale vectorlike T-quarks required to provide adequate values for Cabibbo-Kobayashi-Maskawa (CKM) parameters can also naturally account for the diphoton anomaly. Correlations between $V_{ub}$ and $V_{cb}$ with the vectorlike T-quark mass can be predicted. Should the diphoton anomaly survive in a future run, our proposed interpretation can also be tested in upcoming B and LHC studies.

There has been a great deal of theoretical work on sophisticated charged current quasi-elastic (CCQE) neutrino interaction models in recent years, prompted by a number of experimental results that measured unexpectedly large CCQE cross sections on nuclear targets. As the dominant interaction mode at T2K energies, and the signal process in oscillation analyses, it is important for the T2K experiment to include realistic CCQE cross section uncertainties in T2K analyses. To this end, T2K’s Neutrino Interaction Working Group has implemented a number of recent models in NEUT, T2K’s primary neutrino interaction event generator. In this paper, we give an overview of the models implemented and present fits to published ${\nu }_{\mu }$ and ${\overline{\nu }}_{\mu }$ CCQE cross section measurements from the MiniBooNE and $\mathrm{MINER}\nu \mathrm{A}$ experiments. The results of the fits are used to select a default cross section model for future T2K analyses and to constrain the cross section uncertainties of the model. We find strong tension between datasets for all models investigated. Among the evaluated models, the combination of a modified relativistic Fermi gas with multinucleon CCQE-like interactions gives the most consistent description of the available data.

We explore field theories of a single $p$-form with equations of motions of order strictly equal to 2 and gauge invariance. We give a general method for the classification of such theories which are extensions to the $p$-forms of the Galileon models for scalars. Our classification scheme allows us to compute an upper bound on the number of different such theories depending on $p$ and on the space-time dimension. We are also able to build a nontrivial Galileon-like theory for a 3-form with gauge invariance and an action which is polynomial into the derivatives of the form. This theory has gauge invariant field equations but an action which is not, like a Chern-Simons theory. Hence the recently discovered no-go theorem stating that there are no nontrivial gauge invariant vector Galileons (which we are also able here to confirm with our method) does not extend to other odd-$p$ cases.

We construct a string-inspired model, motivated by the flavored Peccei-Quinn (PQ) axions, as a useful bridge between flavor physics and string theory. The key feature is two anomalous gauged $U(1)$ symmetries, responsible for both the fermion mass hierarchy problem of the standard model and the strong $CP$ problem, that combine string theory with flavor physics and severely constrain the form of the F- and D-term contributions to the potential. In the context of supersymmetric moduli stabilization we stabilize the size moduli with positive masses while leaving two axions massless and one axion massive. We demonstrate that, while the massive gauge bosons eat the two axionic degrees of freedom, two axionic directions survive to low energies as the flavored PQ axions.

We study strange quark matter (SQM) objects ranging from strangelets to strange stars based on our recently proposed unified description. The important interface effects are investigated by adopting a constant surface tension as well as the multiple reflection expansion (MRE) method. It is shown that the properties of SQM objects are strongly affected by the different surface treatments. In the former case, strangelets are more compact, an electric dipole is predicted on the surface of the quark part, and a local minimum of the energy per baryon appears for unusually small values of the surface tension. In the latter case, on the other hand, an electric potential well is formed, and the energy per baryon decreases monotonically with the SQM object’s size. It is found that the MRE scenario coincides with the constant-surface-tension one if realistic values are considered. However, the effects of quark depletion on the quark-vacuum interface cannot be solely described by a constant surface tension. Thus we conclude that the MRE scenario is more reasonable.

The kinematic dynamo (KD) describes the growth of magnetic fields generated by the flow of a conducting medium in the limit of vanishing backaction of the fields onto the flow. The KD is therefore an important model system for understanding astrophysical magnetism. Here, the mathematical correspondence between the KD and a specific stochastic differential equation (SDE) viewed from the perspective of the supersymmetric theory of stochastics (STS) is discussed. The STS is a novel, approximation-free framework to investigate SDEs. The correspondence reported here permits insights from the STS to be applied to the theory of KD and vice versa. It was previously known that the fast KD in the idealistic limit of no magnetic diffusion requires chaotic flows. The KD-STS correspondence shows that this is also true for the diffusive KD. From the STS perspective, the KD possesses a topological supersymmetry, and the dynamo effect can be viewed as its spontaneous breakdown. This supersymmetry breaking can be regarded as the stochastic generalization of the concept of dynamical chaos. As this supersymmetry breaking happens in both the diffusive and the nondiffusive cases, the necessity of the underlying SDE being chaotic is given in either case. The observed exponentially growing and oscillating KD modes prove physically that dynamical spectra of the STS evolution operator that break the topological supersymmetry exist with both real and complex ground state eigenvalues. Finally, we comment on the nonexistence of dynamos for scalar quantities.

Measurements of black-hole spins from gravitational-wave observations of black-hole binaries with ground-based detectors are known to be hampered by partial degeneracies in the gravitational-wave phasing: between the two component spins, and between the spins and the binary’s mass ratio, at least for signals that are dominated by the binary’s inspiral. Through the merger and ringdown, however, a different set of degeneracies apply. This suggests the possibility that, if the inspiral, merger and ringdown are all within the sensitive frequency band of a detector, we may be able to break these degeneracies and more accurately measure both spins. In this work we investigate our ability to measure individual spins for nonprecessing binaries, for a range of configurations and signal strengths, and conclude that in general the spin of the larger black hole will be measurable (at best) with observations from Advanced LIGO and Virgo. This implies that in many applications waveform models parameterized by only one effective spin will be sufficient. Our work does not consider precessing binaries or subdominant harmonics, although we provide some arguments why we expect that these will not qualitatively change our conclusions.

The effects of a power-law Maxwell field on the critical phenomena of higher dimensional dilaton black holes are probed in detail. We successfully derive the analytic solutions of the critical point and carry out some checks to ensure that these critical quantities are positive. It is shown that the constraint on the parameter $\alpha$ describing the strength of the coupling of the electromagnetic field and the scalar field turns out to be $0<{\alpha }^2<1$, which is tighter than that in the nonextended phase space. It is also shown that these critical quantities and the ratio $P_c{v}_c/T_c$ are affected by the power-law Maxwell field. Moreover, critical exponents are found to coincide with those of other anti-de Sitter black holes, showing the powerful influence of mean field theory.

We study structure of solutions of the recently constructed minimal extensions of Einstein’s gravity in four dimensions at the quartic curvature level. The extended higher derivative theory, just like Einstein’s gravity, has only a massless spin-two graviton about its unique maximally symmetric vacuum. The extended theory does not admit the Schwarzschild or Kerr metrics as exact solutions, hence there is no issue of Schwarzschild type singularity but, approximately, outside a source, spherically symmetric metric with the correct Newtonian limit is recovered. We also show that for all Einstein space-times, the square of the Riemann tensor (the Kretschmann scalar or the Gauss-Bonnet invariant) obeys a nonlinear scalar Klein-Gordon equation.

Energetic causal sets are causal sets endowed by a flow of energy-momentum between causally related events. These incorporate a novel mechanism for the emergence of space-time from causal relations [M. Cortês and L. Smolin, Phys. Rev. D 90, 084007 (2014); Phys. Rev. D 90, 044035 (2014)]. Here we construct a spin foam model which is also an energetic causal set model. This model is closely related to the model introduced in parallel by Wolfgang Wieland in [Classical Quantum Gravity 32, 015016 (2015)]. What makes a spin foam model also an energetic causal set is Wieland’s identification of new degrees of freedom analogous to momenta, conserved at events (or four-simplices), whose norms are not mass, but the volume of tetrahedra. This realizes the torsion constraints, which are missing in previous spin foam models, and are needed to relate the connection dynamics to those of the metric, as in general relativity. This identification makes it possible to apply the new mechanism for the emergence of space-time to a spin foam model. Our formulation also makes use of Markopoulou’s causal formulation of spin foams [arXiv:gr-qc/9704013]. These are generated by evolving spin networks with dual Pachner moves. This endows the spin foam history with causal structure given by a partial ordering of the events which are dual to four-simplices.

In the scalar-tensor theories with a massive scalar field, the coupling constants, and the coupling functions in general, which are observationally allowed, can differ significantly from those in the massless case. This fact naturally implies that the scalar-tensor neutron stars with a massive scalar field can have rather different structure and properties in comparison with their counterparts in the massless case and in general relativity. In the present paper, we study slowly rotating neutron stars in scalar-tensor theories with a massive gravitational scalar. Two examples of scalar-tensor theories are examined—the first example is the massive Brans-Dicke theory and the second one is a massive scalar-tensor theory indistinguishable from general relativity in the weak-field limit. In the latter case, we study the effect of the scalar field mass on the spontaneous scalarization of neutron stars. Our numerical results show that the inclusion of a mass term for the scalar field indeed changes the picture drastically compared to the massless case. It turns out that mass, radius, and moment of inertia for neutron stars in massive scalar-tensor theories can differ drastically from the pure general relativistic solutions if sufficiently large masses of the scalar field are considered.