We extend a previous analysis of flavor-changing fermion-graviton vertices, by adding the one loop SM corrections to the flavor diagonal fermion-graviton interactions. Explicit analytical expressions taking into account fermion masses for the on-shell form factors are computed and presented. The infrared safety of the fermion-graviton vertices against radiative corrections of soft photons and gluons is proved, by extending the ordinary infrared cancellation mechanism between real and virtual emissions to the gravity case. These results can be easily generalized to fermion couplings with massive gravitons, graviscalar, and dilaton fields, with potential phenomenological implications to new physics scenarios with low gravity scale.

We extend the analysis of elastic pion-nucleon scattering up to $O(p^4)$ level using the extended-on-mass-shell subtraction scheme within the framework of covariant baryon chiral perturbation theory. Numerical fits to partial wave phase shift data up to $\sqrt{s}=1.13\mathrm{GeV}$ are performed to pin down the free low energy constants. A good description of the existing phase shift data is achieved. We find a good convergence for the chiral series at $O(p^4)$, considerably improved with respect to the $O(p^3)$-level analyses found in previous literature. Also, the leading order contribution from explicit $\Delta (1232)$ resonance and partially-included $\Delta (1232)$ loop contribution are included to describe the phase shift data up to $\sqrt{s}=1.20\mathrm{GeV}$. As phenomenological applications, we investigate chiral corrections to the Goldberger-Treiman relation and find that it converges rapidly, and the $O(p^3)$ correction is found to be very small: $\simeq 0.2\%$. We also get a reasonable prediction of the pion-nucleon sigma term ${\sigma }_{\pi N}$ up to $O(p^4)$ by performing fits including both the pion-nucleon partial wave phase shift data and the lattice QCD data. We report that ${\sigma }_{\pi N}=52\pm 7\mathrm{MeV}$ from the fit without $\Delta (1232)$, and ${\sigma }_{\pi N}=45\pm 6\mathrm{MeV}$ from the fit with explicit $\Delta (1232)$.

We study charged lepton flavor violation in low-scale seesaw models of minimal supergravity, which realize large neutrino Yukawa couplings thanks to approximate lepton-number symmetries. There are two dominant sources of lepton flavor violation in such models. The first source originates from the usual soft supersymmetry-breaking sector, whilst the second one is entirely supersymmetric and comes from the supersymmetric neutrino Yukawa sector. Within the framework of minimal supergravity, we consider both sources of lepton flavor violation, soft and supersymmetric, and calculate a number of possible lepton-flavor-violating transitions, such as the photonic decays of muons and taus, $\mu \to e\gamma$, $\tau \to e\gamma$ and $\tau \to \mu \gamma$, their neutrinoless three-body decays, $\mu \to eee$, $\tau \to eee$, $\tau \to \mu \mu \mu$, $\tau \to ee\mu$ and $\tau \to e\mu \mu$, and the coherent $\mu \to e$ conversion in nuclei. After taking into account the exclusion bounds placed by present experiments of lepton flavor violation, we derive combined theoretical limits on the universal heavy Majorana mass scale $m_N$ and the light-to-heavy neutrino mixings. Supersymmetric low-scale seesaw models offer distinct correlated predictions for lepton-flavor-violating signatures, which might be discovered in current and projected experiments, such as MEG, COMET/PRISM, Mu2e, super-BELLE and LHCb.

Off-shell formulations of supergravities allow one to add closed-form higher-derivative super-invariants that are separately supersymmetric to the usual lower-derivative actions. In this paper we study four-dimensional off-shell $\mathcal{N}=1$ supergravity where additional super-invariants associated with the square of the Weyl tensor and the square of the Ricci scalar are included. We obtain a variety of solutions where the metric describes domain walls, Lifshitz geometries, and also solutions of a kind known as gyratons. We find that in some cases the solutions can be supersymmetric for appropriate choices of the parameters. In some solutions the auxiliary fields may be imaginary. One may reinterpret these as real solutions in an analytically continued theory. Since the supersymmetry transformation rules now require the gravitino to be complex, the analytically continued theory has a “fake supersymmetry” rather than a genuine supersymmetry. Nevertheless, the concept of pseudosupersymmetric solutions is a useful one, since the Killing spinor equations provide first-order equations for the bosonic fields.

The most general form of the Bethe-Salpeter wave functions for the bound states composed of two vector fields of arbitrary spin and definite parity is given. Using the property of vector field ${\partial }_{\mu }{A}_{\mu }(x)=0$, we find that the most general form can be simplified. Then this general form is applied to investigate the bound states composed of two heavy vector mesons and these heavy vector mesons are regarded as resonances. The interaction kernel between two heavy mesons including one light meson $(\sigma ,\omega ,\rho )$ exchange is considered.

A cosmographic reconstruction of $f(\mathcal{T})$ models is here revised in a model independent way by fixing observational bounds on the most relevant terms of the $f(\mathcal{T})$ Taylor expansion. We relate the $f(\mathcal{T})$ models and their derivatives to the cosmographic parameters and then adopt a Monte Carlo analysis. The experimental bounds are thus independent of the choice of a particular $f(\mathcal{T})$ model. The advantage of such an analysis lies on constraining the dynamics of the Universe by reconstructing the form of $f(\mathcal{T})$, without any further assumptions apart from the validity of the cosmological principle and the analyticity of the $f(\mathcal{T})$ function. The main result is to fix model independent cosmographic constraints on the functional form of $f(\mathcal{T})$ which is compatible with the theoretical predictions. Furthermore, we infer a phenomenological expression for $f(\mathcal{T})$, compatible with the current cosmographic bounds and show that small deviations are expected from a constant $f(\mathcal{T})$ term, indicating that the equation of state of dark energy could slightly evolve from the one of the Lambda cold dark model.

We calculate the power emitted in scalar modes for a binary system, including binary pulsars, with a conformal coupling to the most general Galileon effective field theory by considering perturbations around a static, spherical background. While this method is effective for calculating the power in the cubic Galileon case, here we find that if the quartic or quintic Galileon dominate, for realistic pulsar systems the classical perturbative expansion about spherically symmetric backgrounds breaks down (although the quantum effective theory is well defined). The basic reason is that the equations of motion for the fluctuations are then effectively one dimensional. This leads to many multipoles radiating with equal strength, as opposed to the normal Minkowski spacetime and cubic Galileon cases, where increasing multipoles are suppressed by increasing powers of the orbital velocity. We consider the following two cases where perturbation theory gives trustworthy results: (1) when there is a large hierarchy between the masses of two orbiting objects and (2) when we choose scales such that the quartic Galileon only begins to dominate at distances smaller than the inverse pulsar frequency. Implications for future calculations with the full Galileon that account for the Vainshtein mechanism are considered.

We present a new three-dimensional, general-relativistic hydrodynamic evolution scheme coupled to dynamical spacetime evolutions which is capable of efficiently simulating stellar collapse, isolated neutron stars, black hole formation, and binary neutron star coalescence. We make use of a set of adapted curvilinear grids (multipatches) coupled with flux-conservative, cell-centered adaptive mesh refinement. This allows us to significantly enlarge our computational domains while still maintaining high resolution in the gravitational wave extraction zone, the exterior layers of a star, or the region of mass ejection in merging neutron stars. The fluid is evolved with a high-resolution, shock-capturing finite volume scheme, while the spacetime geometry is evolved using fourth-order finite differences. We employ a multirate Runge-Kutta time-integration scheme for efficiency, evolving the fluid with second-order integration and the spacetime geometry with fourth-order integration. We validate our code by a number of benchmark problems: a rotating stellar collapse model, an excited neutron star, neutron star collapse to a black hole, and binary neutron star coalescence. The test problems, especially the latter, greatly benefit from higher resolution in the gravitational wave extraction zone, causally disconnected outer boundaries, and application of Cauchy-characteristic gravitational wave extraction. We show that we are able to extract convergent gravitational wave modes up to $(\ell ,m)=(6,6)$. This study paves the way for more realistic and detailed studies of compact objects and stellar collapse in full three dimensions and in large computational domains. The multipatch infrastructure and the improvements to mesh refinement and hydrodynamics codes discussed in this paper will be made available as part of the open-source Einstein Toolkit.

We construct a background independent model of spacetime from a minimal set of postulates of causality. The topology and geometry of spacetime can be derived from the model, instead of being postulated. We define a measure of causality and relate it to the noncommutative geometric algebra of spacetime coordinates. The geometric algebra formalism leads to the definition of a Euclidean action. The Euclidean action is positive definite and allows the path integral formulation of quantum gravity to be treated as statistical physics of a causal stochastic Markov field.

Higgs inflation is a simple and elegant model in which early-universe inflation is driven by the Higgs sector of the Standard Model. The Higgs sector can support early-universe inflation if it has a large nonminimal coupling to the Ricci spacetime curvature scalar. At energies relevant to such an inflationary epoch, the Goldstone modes of the Higgs sector remain in the spectrum in renormalizable gauges, and hence their effects should be included in the model’s dynamics. We analyze the multifield dynamics of Higgs inflation and find that the multifield effects damp out rapidly after the onset of inflation, because of the gauge symmetry among the scalar fields in this model. Predictions from Higgs inflation for observable quantities, such as the spectral index of the power spectrum of primordial perturbations, therefore revert to their familiar single-field form, in excellent agreement with recent measurements. The methods we develop here may be applied to any multifield model with nonminimal couplings in which the $\mathcal{N}$ fields obey an $SO(\mathcal{N})$ symmetry in field space.

We argue that the existence of the cold dark matter is explained by primordial black holes. We show that a significant number of primordial black holes can be formed in an axionlike curvaton model, in which the highly blue-tilted power spectrum of primordial curvature perturbations is achieved. It is found that the produced black holes with masses $\sim {10}^{20}–{10}^{38}\mathrm{g}$ account for the present cold dark matter. We also argue the possibility of forming the primordial black holes with mass $\sim {10}^5{M}_{\odot }$ as seeds of the supermassive black holes.

We investigate the scalar mode of perturbation of super inflation in the version of loop quantum cosmology in which the gauge invariant holonomy corrections are considered. Given a background solution, we calculate the power spectrum of the perturbation in the classical and loop quantum cosmology conditions. Then we compute the anisotropy originated from the perturbation. It is found that in the presence of the gauge invariant holonomy corrections the power spectrum is exponentially blue and the anisotropy also grows exponentially in the epoch of super inflation.

We develop a formulation where, for an arbitrarily given warp factor, we construct a scalar field action which reproduces the warp factor as a solution of the Einstein equation and field equation corresponding to the action. This formulation could be called the reconstruction. By using the formulation of the reconstruction, we construct models which have an exact solution describing the domain wall. The shape of the domain wall can be flat, de Sitter space-time, or anti-de Sitter space-time. In the constructed domain wall solutions, there often appears a ghost with negative kinetic energy. We give, however, an example of the de Sitter domain wall solution without a ghost, which could be a toy model of inflation. We also investigate the localization of gravity as in the Randall-Sundrum model. It is demonstrated that the four-dimensional Newton law could be reproduced even in the de Sitter space-time domain wall solution. We show that we can construct a space-time, where the domain wall is the general Friedmann-Robertson-Walker universe and the warp factor can be arbitrary. For such a construction, we use two scalar fields. It is also illustrated that the scalar field equations are equivalent to the Bianchi identities: ${\nabla }^{\mu }(R_{\mu \nu }-\frac{1}{2}R{g}_{\mu \nu })=0$.

Superfluid hydrodynamics affects the spin evolution of mature neutron stars and may be key to explaining timing irregularities such as pulsar glitches. However, most models for this phenomenon exclude the global instability required to trigger the event. In this paper we discuss a mechanism that may fill this gap. We establish that small scale inertial r-modes become unstable in a superfluid neutron star that exhibits a rotational lag expected to build up due to vortex pinning as the star spins down. Somewhat counterintuitively, this instability arises due to the (under normal circumstances dissipative) vortex-mediated mutual friction. We explore the nature of the superfluid instability for a simple incompressible model allowing for entrainment coupling between the two fluid components. Our results recover a previously discussed dynamical instability in systems where the two components are strongly coupled. In addition, we demonstrate for the first time that the system is secularly unstable (with a growth time that scales with the mutual friction) throughout much of parameter space. Interestingly, large scale r-modes are also affected by this new aspect of the instability. We analyze the damping effect of shear viscosity, which should be particularly efficient at small scales, arguing that it will not be sufficient to completely suppress the instability in astrophysical systems.

The future asymptotic behavior of a nontitled Bianchi type IV viscous fluid model is analyzed. In particular, we consider the case of a viscous fluid without heat conduction and constant expansion-normalized bulk and shear viscosity coefficients. We show using dynamical systems theory that the only future attracting equilibrium points are the flat Friedmann-LeMaitre solution, the open Friedmann-LeMaitre solution, and the isotropic Milne universe solution. We also show the bifurcations exist with respect to an increasing expansion-normalized bulk viscosity coefficient. It is finally shown through an extensive numerical analysis that the dynamical system isotropizes at late times.

$WW$ scattering is dominated at high energies by their longitudinal components, which are the most sensitive to the nature of the electroweak symmetry breaking. Prior to the discovery at the LHC of a Higgs-like particle, unitarization tools were extensively used to show that, in the absence of a light Higgs boson, new resonances resulting from the would-be strongly interacting electroweak sector would appear, and furthermore these techniques would approximately predict their masses, widths, and signal strengths. With the discovery of a Higgs-like particle now firmly established, we reinvestigate these techniques assuming this particle couples exactly as in the standard model (SM), but still being open to the possibility of an extended symmetry breaking sector. While the SM itself is free from problems with perturbative unitarity in the electroweak sector, “anomalous” self-couplings of the vector bosons—low-energy remnants of such higher-energy symmetry breaking sectors—are easily shown to reintroduce them. We demonstrate how new resonances should still appear in the scattering of electroweak vector bosons after imposing constraints from unitarity, and we discuss their ability to be probed with current and future LHC data.

We discuss the connections between the recently observed Higgs-like particle and rare $B$ decays in the context of two Higgs doublet models (2HDMs). The measured decays of the Higgs boson to fermions and gauge bosons, along with the observation of the decay $B_s\to {\mu }^{+}{\mu }^{-}$, place stringent restrictions on the allowed parameter space of two Higgs doublet models. Future measurements of $h^0\to \gamma \gamma$ can potentially exclude Type I 2HDMs, while the parameters of other 2HDMs are already severely restricted. The recent observations of the $h^0\to {\tau }^{+}{\tau }^{-}$ and $h^0\to b\overline{b}$ decays further constrain the models.

We have revisited the calculation of the neutron electric dipole moment in the presence of the $CP$-violating operators up to dimension 5 based on the chiral perturbation theory. In particular, we focus on the contribution of strangeness content. In the calculation, we extract the nucleon matrix elements of scalar-type quark operators from the results of the lattice QCD simulations, while those of the dipole-type quark-gluon operators are evaluated by using the method of the QCD sum rules. As a result, it is found that although the strangeness quantity in nucleons is small, the contribution of the chromoelectric dipole moment of strange quarks may still be sizable, and thus may offer a sensitive probe for the $CP$-violating interactions in physics beyond the Standard Model.

We explore two bilarge neutrino mixing Anzätze within the context of Abelian flavor symmetry theories: (${\mathtt{B}\mathtt{L}}_{\mathtt{1}}$) $\sin {\theta }_{12}\sim \lambda$, $\sin {\theta }_{13}\sim \lambda$, $\sin {\theta }_{23}\sim \lambda$, and (${\mathtt{B}\mathtt{L}}_{\mathtt{2}}$) $\sin {\theta }_{12}\sim \lambda$, $\sin {\theta }_{13}\sim \lambda$, $\sin {\theta }_{23}\sim 1-\lambda$. The first pattern is proposed by two of us and is favored if the atmospheric mixing angle ${\theta }_{23}$ lies in the first octant, while the second one is preferred for the second octant of ${\theta }_{23}$. In order to reproduce the second texture, we find that the flavor symmetry should be $U(1)\times Z_m$, while for the first pattern the flavor symmetry should be extended to $U(1)\times Z_m\times Z_n$ with $m$ and $n$ of different parity. Explicit models for both mixing patterns are constructed based on the flavor symmetries $U(1)\times Z_3\times Z_4$ and $U(1)\times Z_2$. The models are extended to the quark sector within the framework of $SU(5)$ grand unified theory in order to give a successful description of quark and lepton masses and mixing simultaneously. Phenomenological implications are discussed.

Using the group theory of mixing to examine all finite subgroups of $SU(3)$ with an order less than 512, we found recently that only the group $\Delta (150)$ can give rise to a correct reactor angle ${\theta }_{13}$ of neutrino mixing without any free parameters. It predicts ${sin}^{2}2{\theta }_{13}=0.11$ and a submaximal atmospheric angle with ${sin}^{2}2{\theta }_{23}=0.94$, in good agreement with experiment. The solar angle ${\theta }_{12}$, the charge conjugation-parity phase $\delta$, and the neutrino masses $m_i$ are left as free parameters. In this article we provide more details of this case and discuss possible gains and losses by introducing right-handed symmetries and/or valons to construct dynamical models. A simple model is discussed where the solar angle agrees with experiment and all its mixing parameters can be obtained from the group $\Delta (600)$ by symmetry alone. The promotion of $\Delta (150)$ to $\Delta (600)$ is, on one hand, analogous to the promotion of $S_3$ to $S_4$ in the presence of tribimaximal mixing, and on the other hand, it is similar to the extension from $A_4$ to $S_4$ in that case.