Millimeter-wavelength very-long-baseline-interferometry observations of the supermassive black holes in Sgr A* and M87 by the Event Horizon Telescope could potentially trace the dynamics of ejected plasma blobs in real time. We demonstrate that the trajectory and tidal stretching of these blobs can be used to test general relativity and set new constraints on the mass and spin of these black holes.

We present a nonperturbative calculation of the strangeness of the nucleon $y_N$ within the framework of lattice QCD. This observable is known to be an important cornerstone to interpret results from direct dark matter detection experiments. We perform a lattice computation for $y_N$ with an analysis of systematic effects originating from discretization, finite size, chiral extrapolation and excited state effects leading to the value of $y_N=0.173(50)$. The rather large uncertainty of this value of $y_N$ is dominated by systematic uncertainties which we are able to quantify in this work.

Current experimental information on the charm-meson decay observables in which the $c\to s\ell {\nu }_{\ell }$ transitions occur is well compatible with the Standard Model predictions. Recent precise lattice calculations of the $D_s$-meson decay constant and form factors in $D\to K\ell \nu$ decays offer a possibility to search for small deviations from the Standard Model predictions in the next generation of high-intensity flavor experiments. We revisit constraints from these processes on the new physics contributions in the effective theory approach. We investigate new physics effects which might appear in the differential distributions for the longitudinally and transversely polarized $K^{*}$ in $D\to K^{*}\ell {\nu }_{\ell }$ decays. Present constraints from these observables are rather weak, but could be used to constrain new physics effects in the future. In the case of $D\to K\ell \nu$ we identify observables sensitive to the new physics contribution coming from the scalar Wilson coefficient, namely the forward-backward asymmetry and the transversal muon polarizations. By assuming that new physics only modifies the second lepton generation, we identify the allowed region for the differential decay rate for the process $D\to K\mu {\nu }_{\mu }$ and find that it is allowed to deviate from the Standard Model prediction by only a few percent. The lepton flavor universality violation can be tested in the ratio $R_{\mu /e}(q^2)\equiv \frac{d{\mathrm{\Gamma }}^{(\mu )}}{d{q}^2}/\frac{d{\mathrm{\Gamma }}^{(e)}}{d{q}^2}$. If the first lepton generation behaves as in the Standard Model, we find (using the current constraint on the scalar Wilson coefficient) that the ratio $R_{\mu /e}(q^2)$ is currently allowed to be within the range (0.9,1.2), depending on the value of $q^2$.

A search for sidereal variations in the force between two planar tungsten oscillators separated by about $80\mu \mathrm{m}$ sets the first experimental limits on Lorentz violation involving quadratic couplings of the Riemann curvature, consistent with no effect at the level of $10^{-7}{\mathrm{m}}^2$.

The concept of spin-base invariance is extended to arbitrary integer dimension $d\ge 2$. Explicit formulas for the spin connection as a function of the Dirac matrices are found. We disclose the hidden spin-base invariance of the vielbein formalism and give a detailed motivation for this symmetry from first principles. The common Lorentz symmetric gauge for the vielbein is constructed for the Dirac matrices, even for metrics which are not linearly connected. Under certain criteria, it constitutes the simplest possible gauge, demonstrating why this gauge is so useful.

Quantum inequalities bound the extent to which weighted time averages of the renormalized energy density of a quantum field can be negative. Such inequalities in curved spacetime can be used to disprove the existence of exotic phenomena, such as closed timelike curves. Starting with a general result of Fewster and Smith, we derive a quantum inequality for a minimally coupled scalar field on a geodesic in a spacetime with small curvature, working to first order in the Ricci tensor and its derivatives. Since only the Ricci tensor enters, there are no first-order corrections to the flat-space quantum inequality on paths which do not encounter any matter or energy.

We study topological black hole solutions of the simplest quadratic gravity action and we find that two classes are allowed. The first is asymptotically flat and mimics the Reissner-Nordström solution, while the second is asymptotically de Sitter or anti–de Sitter. In both classes, the geometry of the horizon can be spherical, toroidal or hyperbolic. We focus, in particular, on the thermodynamical properties of the asymptotically anti–de Sitter solutions and we compute the entropy and the internal energy with Euclidean methods. We find that the entropy is positive-definite for all horizon geometries and this allows us to formulate a consistent generalized first law of black hole thermodynamics, which keeps in account the presence of two arbitrary parameters in the solution. The two-dimensional thermodynamical state space is fully characterized by the underlying scale invariance of the action and it has the structure of a projective space. We find a kind of duality between black holes and other objects with the same entropy in the state space. We briefly discuss the extension of our results to more general quadratic actions.

We study the emergent scenario, which is proposed to avoid the big bang singularity, in the Einstein-Cartan (EC) theory with a positive cosmological constant and a perfect fluid by analyzing the existence and stability of the Einstein static (ES) solutions. We find that there is no stable ES solution for a spatially flat or open universe. However, for a spatially closed universe, the stable ES solution does exist, and in the same existence parameter regions, there also exists an unstable one. With the slow decrease of the equation of state $w$ of the perfect fluid, the stable and unstable critical points move close gradually and coincide once $w$ reaches a critical value, so that the stable critical point becomes an unstable one. As a result, if $w$ approaches a constant at $t\to -\infty$, the universe can stay at the stable ES state past eternally, and furthermore it can naturally exit from this state and evolve into an inflationary era if $w$ decreases slowly as time goes forward. Therefore, the emergent scenario that avoids the big bang singularity can be successfully implemented in the EC theory of gravity.

The search for non-Newtonian forces has been pursued following many different paths. Recently it was suggested that hypothetical chameleon interactions, which might explain the mechanisms behind dark energy, could be detected in a high-precision force measurement. In such an experiment, interactions between parallel plates kept at constant separation could be measured as a function of the pressure of an ambient gas, thereby identifying chameleon interactions by their unique inverse dependence on the local mass density. During the past years we have been developing a new kind of setup complying with the stringent requirements of the proposed experiment. In this article we present the first and most important part of this setup—the force sensor. We discuss its design, fabrication, and characterization. From the results of the latter, we derive limits on chameleon interaction parameters that could be set by the forthcoming experiment. Finally, we describe the opportunity to use the same setup to measure Casimir forces at large surface separations with unprecedented accuracy, thereby potentially giving unambiguous answers to long-standing open questions.

We calculate differential cross sections for exclusive production of heavy charged scalar, weakly interacting particles (charged Higgs bosons, charged technipions, etc.) via photon-photon exchanges in the $pp\to pp{H}^{+}{H}^{-}$ reaction with exact $2\to 4$ kinematics. We present distributions in rapidities, transverse momenta, and correlations in azimuthal angles between the protons and between the charged Higgs bosons. As an example, the integrated cross section for $\sqrt{s}=14\mathrm{TeV}$ (LHC) is about 0.1 fb and about 0.9 fb at the Future Circular Collider (FCC) for $\sqrt{s}=100\mathrm{TeV}$ when assuming $m_{H^{\pm }}=150\mathrm{GeV}$. The results are compared with results obtained within standard equivalent-photon approximation known from the literature. We discuss the role of the Dirac and Pauli electromagnetic form factors of the proton. We have also performed first calculations of cross sections for the exclusive diffractive Khoze-Martin-Ryskin mechanism. We have estimated limits on the $g_{h{H}^{+}{H}^{-}}$ coupling constant within the two-Higgs doublet model based on recent experimental data from the LHC. The diffractive contribution is, however, much smaller than the $\gamma \gamma$ one. The $Z\gamma$, $\gamma Z$, and $ZZ$ exchanges give even smaller contributions. Absorption corrections are calculated for the first time differentially for various distributions. In general, they lead to a damping of the cross section. The damping depends on the $M_{H^{+}{H}^{-}}$ invariant mass and on $t$ four-momentum transfers squared. In contrast to diffractive processes, the larger the collision energy, the smaller the effect of absorption. We discuss a possibility to measure the exclusive production of two charged Higgs bosons with the help of so-called “forward proton detectors” at the LHC experiments.

We investigate the production and detection prospects for the quintuplet heavy leptons at the LHC in the context of a new model which is proposed as a viable and testable solution to the neutrino mass problem. We classify the signals, carry out a full simulation on the signals and the relevant backgrounds at the 14 TeV LHC. After applying suitable kinematic cuts, the background events are substantially suppressed. The signals of the heavy leptons might be detected at the 14 TeV LHC.

The very special relativity electroweak Standard Model (VSR EW SM) is a theory with $\mathrm{SU}(2{)}_L\times \mathrm{U}(1{)}_R$ symmetry, with the same number of leptons and gauge fields as in the usual Weinberg-Salam model. No new particles are introduced. The model is renormalizable and unitarity is preserved. However, photons obtain mass and the massive bosons obtain different masses for different polarizations. Besides, neutrino masses are generated. A VSR-invariant term will produce neutrino oscillations and new processes are allowed. In particular, we compute the rate of the decays $\mu \to e+\gamma$. All these processes, which are forbidden in the electroweak Standard Model, put stringent bounds on the parameters of our model and measure the violation of Lorentz invariance. We investigate the canonical quantization of this nonlocal model. Second quantization is carried out, and we obtain a well-defined particle content. Additionally, we do a counting of the degrees of freedom associated with the gauge bosons involved in this work, after spontaneous symmetry breaking has been realized. Violations of Lorentz invariance have been predicted by several theories of quantum gravity [J. Alfaro, H. Morales-Tecotl, and L. F. Urrutia, Phys. Rev. Lett. 84, 2318 (2000); Phys. Rev. D 65, 103509 (2002)]. It is a remarkable possibility that the low-energy effects of Lorentz violation induced by quantum gravity could be contained in the nonlocal terms of the VSR EW SM.

We discuss the consistency of a recently proposed class of theories described by an arbitrary function of the Ricci scalar, the trace of the energy-momentum tensor, and the contraction of the Ricci tensor with the energy-momentum tensor. We briefly discuss the limitations of including the energy-momentum tensor in the action, as it is a nonfundamental quantity but a quantity that should be derived from the action. The fact that theories containing nonlinear contractions of the Ricci tensor usually lead to the presence of pathologies associated with higher-order equations of motion will be shown to constrain the stability of this class of theories. We provide a general framework and show that the conformal and nonminimal couplings to the matter fields usually lead to higher-order equations of motion. To illustrate such limitations, we explicitly study the cases of a canonical scalar field, a $K$-essence field, and a massive vector field, whereas for the scalar field cases, it is possible to find healthy theories, and for the vector field case, the presence of instabilities is unavoidable.

We use astrophysical and atomic clock tests of the stability of the fine-structure constant $\alpha$, together with type Ia supernova and Hubble parameter data, to constrain the simplest class of dynamical dark energy models where the same degree of freedom is assumed to provide both the dark energy and (through a dimensionless coupling $\zeta$ to the electromagnetic sector) the $\alpha$ variation. We show how current data tightly constrain a combination of $\zeta$ and the dark energy equation of state $w_0$. At the 95% confidence level and marginalizing over $w_0$ we find $|\zeta |<5\times {10}^{-6}$, with the atomic clock tests dominating the constraints. The forthcoming generation of high-resolution ultrastable spectrographs will enable significantly tighter constraints.

We consider a variant of TeV-scale seesaw models in which three additional heavy right-handed neutrinos are added to the standard model to generate the quasidegenerate light neutrinos. This model is theoretically interesting since it can be fully rebuilt from the experimental data of neutrino oscillations except for an unknown factor in the Dirac-Yukawa coupling. We study the constraints on this coupling coming from metastability of electroweak vacuum. An even stronger bound comes from the lepton flavor violating decays on this model, especially in a heavy neutrino mass scenario which is within the collider’s reach. Bestowed with these constrained parameters, we explore the production and discovery potential coming from these heavy neutrinos at the 14 TeV run of the Large Hadron Collider. Signatures with trilepton final state together with backgrounds are considered in a realistic simulation.

We study a grand unified theories inspired supersymmetric model with nonuniversal gaugino masses that can explain the observed muon $g-2$ anomaly while simultaneously accommodating an enhancement or suppression in the $h\to \gamma \gamma$ decay channel. In order to accommodate these observations and $m_h\simeq 125$ to 126 GeV, the model requires a spectrum consisting of relatively light sleptons whereas the colored sparticles are heavy. The predicted stau mass range corresponding to $R_{\gamma \gamma }\ge 1.1$ is $100\mathrm{GeV}\lesssim m_{\tilde{\tau }}\lesssim 200\mathrm{GeV}$. The constraint on the slepton masses, particularly on the smuons, arising from considerations of muon $g-2$ is somewhat milder. The slepton masses in this case are predicted to lie in the few hundred GeV range. The colored sparticles turn out to be considerably heavier with $m_{\tilde{g}}\gtrsim 4.5\mathrm{TeV}$ and $m_{{\tilde{t}}_1}\gtrsim 3.5\mathrm{TeV}$, which makes it challenging for these to be observed at the 14 TeV LHC.

We present the ground and excited state spectra of doubly charmed baryons from lattice QCD with dynamical quark fields. Calculations are performed on anisotropic lattices of size $16^3\times 128$, with inverse spacing in temporal direction $a_t^{-1}=5.67(4)\mathrm{GeV}$ and with a pion mass of about 390 MeV. A large set of baryonic operators that respect the symmetries of the lattice yet which retain a memory of their continuum analogues are used. These operators transform as irreducible representations of ${\mathrm{SU}(3)}_F$ symmetry for flavor, SU(4) symmetry for Dirac spins of quarks and O(3) for spatial symmetry. The distillation method is utilized to generate baryon correlation functions which are analyzed using the variational fitting method to extract excited states. The lattice spectra obtained have baryonic states with well-defined total spins up to $7/2$ and the pattern of low-lying states does not support the diquark picture for doubly charmed baryons. On the contrary the calculated spectra are remarkably similar to the expectations from models with an $\mathrm{SU}(6)\times \mathrm{O}(3)$ symmetry. Various spin-dependent energy splittings between the extracted states are also evaluated.

We study the strangeness $+1$ meson-baryon systems to obtain improved $KN$ and $K^{*}N$ amplitudes and to look for a possible resonance formation by the $KN\text{−}{K}^{*}N$ coupled interaction. We obtain amplitudes for light vector meson–baryon systems by implementing the $s$-, $t$- and $u$-channel diagrams and a contact interaction. The pseudoscalar meson-baryon interactions are obtained by relying on the Weinberg-Tomozawa theorem. The transition amplitudes between the systems consisting of pseudoscalars and vector mesons are calculated by extending the Kroll-Ruderman term for pion photoproduction by replacing the photon by a vector meson. We fix the subtraction constants required to calculate the loops by fitting our $KN$ amplitudes to the data available for the isospin 0 and 1 $s$-wave phase shifts. We provide the scattering lengths and the total cross sections for the $KN$ and $K^{*}N$ systems obtained in our model, which can be useful in future in-medium calculations. Our amplitudes do not correspond to the formation of a resonance in any of the isospin and spin configurations.

We study the process $e^{-}{e}^{+}\to \gamma H$, where $H$ represents $H_{\mathrm{SM}}$, $h^0$, or $H^0$. This process occurs at the one loop level in the standard model or in the minimal supersymmetric standard model (MSSM). We establish supersimple (sim) high energy expressions for all helicity amplitudes of this process, and we identify their level of accuracy for describing the various polarized and unpolarized observables, and for distinguishing SM from MSSM or another beyond the standard model. We pay special attention to transverse $e^{\mp }$ polarization and azimuthal dependencies induced by the imaginary parts of the amplitudes, which are relatively important in this process.

The first- and second-order forms of gauge theories are classically equivalent; we consider the consequence of quantizing the first-order form using the Faddeev-Popov approach. Both the Yang-Mills and the Einstein-Hilbert actions are considered. An advantage of this approach is that the interaction vertices are quite simple, being independent of momenta. However, it is necessary to consider the propagator for two fields (including a mixed propagator). We derive the Feynman rules for both models and consider the one-loop correction for the thermal energy momentum tensor.