We investigate the forward-backward asymmetries in the pair production of fourth-family fermions through the new $Z^{\prime }$ interactions in $e^{+}{e}^{-}$ collisions. A $Z^{\prime }$ boson with family-universal couplings can contribute to the pair production of fourth-family fermions via the $s$-channel exchange. Linear colliders provide a clean environment for the physics of the $Z^{\prime }$ boson in order to measure its couplings precisely. The effects of the $Z^{\prime }$ boson on the asymmetries are shown to be important in some parameter regions for different $Z^{\prime }$ models. Among these parameters, the invariant mass distribution $m_{F\overline{F}}$ will be an important measurement to constrain the $Z^{\prime }$ models. Providing that fourth-family fermions exist in an accesssible mass range, a ${\chi }^2$ analysis can be used to probe the $Z^{\prime }$ models at linear colliders.

The binding energies of a range of nuclei and hypernuclei with atomic number $A\le 4$ and strangeness $|s|\le 2$, including the deuteron, dineutron, H-dibaryon, ${}^3\mathrm{He}$, ${}_{\Lambda }{}^3\mathrm{He}$, ${}^4\mathrm{He}$, ${}_{\Lambda }{}^4\mathrm{He}$, and ${}_{\Lambda \Lambda }{}^4\mathrm{He}$, are calculated in the limit of flavor-SU(3) symmetry at the physical strange-quark mass with quantum chromodynamics (without electromagnetic interactions). The nuclear states are extracted from lattice QCD calculations performed with $n_f=3$ dynamical light quarks using an isotropic clover discretization of the quark action in three lattice volumes of spatial extent $L\sim 3.4\mathrm{fm}$, 4.5 fm, and 6.7 fm, and with a single lattice spacing $b\sim 0.145\mathrm{fm}$.

We compute the color fields of SU(3) lattice QCD created by static pentaquark systems, in a ${24}^3\times 48$ lattice at $\beta =6.2$ corresponding to a lattice spacing $a=0.07261(85)\mathrm{fm}$. We find that the pentaquark color fields are well described by a multi-Y-type shaped flux tube. The flux tube junction points are compatible with Fermat-Steiner points minimizing the total flux tube length. We also compare the pentaquark flux tube profile with the diquark-diantiquark central flux tube profile in the tetraquark and the quark-antiquark fundamental flux tube profile in the meson, and they match, thus showing that the pentaquark flux tubes are composed of fundamental flux tubes.

We match the continuum and lattice axial-vector and vector currents at one loop in perturbation theory. For the heavy quarks we use the nonrelativistic QCD (NRQCD) action and for the light quarks the highly improved staggered quark (HISQ) action. We present results for both massless and massive HISQ quarks and as part of the matching procedure we include a discussion of the one loop HISQ renormalization parameters.

We analyze the angular distributions of $\overline{B}\to {\overline{K}}^{*}(\to \overline{K}\pi ){\ell }^{+}{\ell }^{-}$ and $\overline{B}\to \overline{K}{\ell }^{+}{\ell }^{-}$ decays in the region of low hadronic recoil in a model-independent way by taking into account the complete set of dimension-six operators $[\overline{s}\Gamma b][\overline{\ell }{\Gamma }^{\prime }\ell ]$. We obtain several novel low-recoil observables with high sensitivity to nonstandard-model Dirac structures, including $CP$ asymmetries, which do not require flavor tagging. The transversity observables $H_T^{(1,3,4,5)}$ are found to be insensitive to hadronic matrix elements and their uncertainties even when considering the complete set of operators. In the most general scenario we show that the low recoil operator product expansion can be probed at the few-percent level using the angular observable $J_7$. Higher sensitivities are possible assuming no tensor contributions, specifically by testing the low-recoil relation $|H_T^{(1)}|=1$. We explicitly demonstrate the gain in reach of the low-recoil observables in accessing the ratio $|{\mathcal{C}}_9/{\mathcal{C}}_{10}|$ compared to the forward-backward asymmetry, and probing $CP$-violating right-handed currents $\mathrm{Im}{\mathcal{C}}_{{10}^{\prime }}$. We give updated Standard Model predictions for key observables in $\overline{B}\to {\overline{K}}^{(*)}{\ell }^{+}{\ell }^{-}$ decays.

We study the physics potential of future long-baseline neutrino oscillation experiments at large ${\theta }_{13}$, focusing especially on systematic uncertainties. We discuss superbeams, beta beams, and neutrino factories, and for the first time compare these experiments on an equal footing with respect to systematic errors. We explicitly simulate near detectors for all experiments; we use the same implementation of systematic uncertainties for all experiments; and we fully correlate the uncertainties among detectors, oscillation channels, and beam polarizations as appropriate. As our primary performance indicator, we use the achievable precision in the measurement of the $CP$-violating phase $\delta$. We find that a neutrino factory is the only instrument that can measure $\delta$ with a precision similar to that of its quark sector counterpart. All neutrino beams operating at peak energies $\gtrsim 2\mathrm{GeV}$ are quite robust with respect to systematic uncertainties, whereas especially beta beams and $\mathsf{T}\mathsf{2}\mathsf{H}\mathsf{K}$ suffer from large cross-section uncertainties in the quasielastic regime, combined with their inability to measure the appearance signal cross sections at the near detector. A noteworthy exception is the combination of a $\gamma =100$ beta beam with an $\mathsf{S}\mathsf{P}\mathsf{L}$-based superbeam, in which all relevant cross sections can be measured in a self-consistent way. This provides a performance second only to that of the neutrino factory. For other superbeam experiments such as $\mathsf{L}\mathsf{B}\mathsf{N}\mathsf{O}$ and the setups studied in the context of the $\mathsf{L}\mathsf{B}\mathsf{N}\mathsf{E}$ reconfiguration effort, statistics turns out to be the bottleneck. In almost all cases, the near detector is not critical to control systematics, since the combined fit of appearance and disappearance data already constrains the impact of systematics to be small, provided that the three-active-flavor oscillation framework is valid.

The decays of a Higgs boson to the $\gamma \gamma$ and $Z\gamma$ final states are purely quantum mechanical phenomena that are closely related to each other. We study the effects of an extended Higgs sector on the decay rates of the two modes. We propose that a simultaneous determination of them and the $ZZ$ mode is a useful way to see whether the Higgs boson recently observed by the LHC experiments is of the standard model type or could be a member of a larger Higgs sector.

We show that the simplest supersymmetric scenario where a large Higgs mass can be attained at tree level for any ratio of the Higgs vacuum expectation values corresponds to the case where the neutrino masses are generated through the type II seesaw mechanism. This allows a standard model-like Higgs with mass around 125 GeV without assuming a heavy spectrum for the top squarks. We show that our results are consistent with the bounds coming from perturbativity up to the grand unified scale and discuss gauge coupling unification and possible signals at the Large Hadron Collider.

We calculate the linear vacuum perturbations of a Kerr black hole surrounded by a slowly varying external spacetime to third order in the ratio of the black-hole mass to the radius of curvature of the external spacetime. This expansion applies to two relevant physical scenarios: (i) a small Kerr black hole immersed in the gravitational field of a much larger external black hole, and (ii) a Kerr black hole moving slowly around another external black hole of comparable mass. This small-hole/slow-motion approximation allows us to parametrize the perturbation through slowly varying, time-dependent electric and magnetic tidal tensors, which then enable us to separate the Teukolsky equation and compute the Newman-Penrose scalar analytically to third order in our expansion parameter. We obtain generic expressions for the mass and angular momentum flux through the perturbed black hole horizon, as well as the rate of change of the horizon surface area, in terms of certain invariants constructed from the electric and magnetic tidal tensors. We conclude by applying these results to the second scenario described above.

Dynamical dark energy (DE) phenomenon emerges as a geometrical effect accompanying the cosmological expansion of nonrelativistic fermionic matter. This occurs without the need for any fluid, like dynamical scalar field (quintessence, cosmon, etc.), and with conventional form of the Einstein equations in contrast to other known geometrical DE models. The phenomenon results from first principles in the framework of the two measures field theory where, in the Einstein frame, both fermion masses and the cosmological constant (CC) turn into functions of the cold fermion density $n$. This $n$ dependence becomes negligible in regular (laboratory) conditions, but it may have an important role in cosmology. In the 4D gravity model where the original action involves only CC and massive fermions without self-interaction, for different (but wide) regions in the parameter space, we have found two possible classes of scenarios for the late universe starting from the cold matter domination era. We argue that the fermions which drive the variable CC should be associated with cold neutrinos disposed in voids and supervoids. The cosmological dynamics of the first class practically coincides with that of the $\Lambda \mathrm{CDM}$ model, while the dynamics of the second class is of the phantomlike regime with a pseudo-rip scenario. Crossing the phantom divide happens due to a new type of the neutrino DE effect where neutrinos pass through the state with zero mass and with the vacuumlike EoS $P_{\nu }=-{\rho }_{\nu }$.

Growing neutrino quintessence addresses the why now problem of dark energy by assuming that the neutrinos are coupled to the dark energy scalar field. The coupling mediates an attractive force between the neutrinos leading to the formation of large neutrino lumps. This work proposes an effective, simplified description of the subsequent cosmological dynamics. We treat neutrino lumps as effective particles and investigate their properties and mutual interactions. The neutrino lump fluid behaves as cold dark matter coupled to dark energy. The methods developed here may find wider applications for fluids of composite objects.

The cosmological backreaction from perturbations is clearly gauge dependent, and obviously depends on the choice of averaged Hubble rate. We consider two common choices of Hubble rate and advocate the use of comoving volume-preserving gauges. We highlight two examples valid to an appropriate order in perturbation theory—uniform curvature gauge, which is as close to volume-preserving as possible, and a spatially-traceless uniform cold dark matter gauge, which preserves the volume to linear order. We demonstrate the strong gauge and frame dependences in averaging. In traceless uniform cold dark matter gauge the backreaction exhibits a strong ultraviolet divergence and can be tuned to an arbitrary magnitude with an appropriate choice of smoothing scale. In uniform curvature gauge, we find that for a choice of Hubble rate locked to the spatial surface, the backreaction vanishes identically, while for a Hubble rate defined from a fluid’s expansion scalar, the effective energy density at the current epoch in an Einstein–de Sitter universe is ${\Omega }_{\mathrm{eff}}\approx 5\times {10}^{-4}$, slightly bigger than, but in broad agreement with, previous results in conformal Newtonian gauge.

The evolution of the nonadiabatic pressure perturbation during inflation driven by two scalar fields is studied numerically for three different types of models. In the first model, the fields have standard kinetic terms. The other two models considered feature noncanonical kinetic terms, the first containing two fields which are coupled via their kinetic terms and the second where one field has the standard kinetic term with the other field being a Dirac-Born-Infeld field. We find that the evolution and the final amplitude of the nonadiabatic pressure perturbation depends strongly on the kinetic terms.

We examine Hubeny’s scenario according to which a near-extremal Reissner-Nordström black hole can absorb a charged particle and be driven toward an over-extremal state in which the charge exceeds the mass, signaling the destruction of the black hole. Our analysis incorporates the particle’s electromagnetic self-force and the energy radiated to infinity in the form of electromagnetic waves. With these essential ingredients, our sampling of the parameter space reveals no instances of an overcharged final state, and we conjecture that the self-force acts as a cosmic censor, preventing the destruction of a near-extremal black hole by the absorption of a charged particle. We argue, on the basis of the third law of black hole mechanics, that this conclusion is robust and should apply to attempts to overspin a Kerr black hole.

We analyze the nucleon’s Compton scattering amplitude in the Dyson-Schwinger/Faddeev approach. We calculate a subset of diagrams that implements the nonperturbative handbag contribution as well as all $t$-channel resonances. At the quark level, these ingredients are represented by the quark Compton vertex whose analytic properties we study in detail. We derive a general form for a fermion two-photon vertex that is consistent with its Ward-Takahashi identities and free of kinematic singularities, and we relate its transverse part to the on-shell nucleon Compton amplitude. We solve an inhomogeneous Bethe-Salpeter equation for the quark Compton vertex in rainbow-ladder truncation and implement it in the nucleon Compton scattering amplitude. The remaining ingredients are the dressed quark propagator and the nucleon’s bound-state amplitude which are consistently solved from Dyson-Schwinger and covariant Faddeev equations. We verify numerically that the resulting quark Compton vertex and nucleon Compton amplitude both reproduce the $\pi \gamma \gamma$ transition form factor when the pion pole in the $t$ channel is approached.

We consider the phenomenology of a dimension-four operator that violates electromagnetic gauge invariance. Its magnitude is severely constrained by the lack of scattering of very low-energy electromagnetic radiation off of the cosmic microwave background and by the lack of an induced mass when photons propagate in the cosmic microwave background. We also discuss possible Lorentz-violating extensions of the operator basis. If a bare Proca mass exists and dominates over the induced mass, there is also a tight constraint from high-energy scattering.

We determine the strange quark condensate from lattice QCD for the first time and compare its value to that of the light quark and chiral condensates. The results come from a direct calculation of the expectation value of the trace of the quark propagator followed by subtraction of the appropriate perturbative contribution, derived here, to convert the non-normal-ordered $m\overline{\psi }\psi$ to the $\overline{\mathrm{MS}}$ scheme at a fixed scale. This is then a well-defined physical “nonperturbative” condensate that can be used in the operator product expansion of current-current correlators. The perturbative subtraction is calculated through $\mathcal{O}({\alpha }_s)$ and estimates of higher order terms are included through fitting results at multiple lattice spacing values. The gluon field configurations used are “second generation” ensembles from the MILC collaboration that include $2+1+1$ flavors of sea quarks implemented with the highly improved staggered quark action and including $u/d$ sea quarks down to physical masses. Our results are $⟨\overline{s}s{⟩}^{\overline{\mathrm{MS}}}(2\mathrm{GeV})=-(290(15)\mathrm{MeV}{)}^3$, $⟨\overline{l}l{⟩}^{\overline{\mathrm{MS}}}(2\mathrm{GeV})=-(283(2)\mathrm{MeV}{)}^3$, where $l$ is a light quark with mass equal to the average of the $u$ and $d$ quarks. The strange to light quark condensate ratio is 1.08(16). The light quark condensate is significantly larger than the chiral condensate in line with expectations from chiral analyses. We discuss the implications of these results for other calculations.

We discuss QCD radiative corrections to the production of a heavy neutral resonance $Z^{\prime }$ at the LHC assuming that it decays into a $t\overline{t}$ final state. Compared to previous studies, our computation includes top quark decays as well as interference between the $Z^{\prime }$ signal process and the QCD $t\overline{t}$ background. The interference contribution appears for the first time at next-to-leading order QCD and requires new one-loop amplitudes that are not present when signal and background are treated separately. We describe some examples of how QCD radiative corrections may influence both the exclusion limits and studies of properties of the new resonance, once it is discovered.

We investigate the resummation of large logarithmic perturbative corrections to hadron production in electron-positron annihilation and semi-inclusive deep-inelastic scattering. We find modest, but significant, enhancements of hadron multiplicities in the kinematic regimes accessible in present high-precision experiments. Our results are therefore relevant for the determination of hadron fragmentation functions from data for these processes.

We present a refined calculation of the quark-loop contribution to hadronic light-by-light scattering that focuses upon the impact of the transverse components of the quark-photon vertex. These structures are compared and contrasted with those found within the extended Nambu-Jona-Lasinio models. We discuss similarities and differences between the two approaches and further clarify the important role of momentum dependent dressing functions. As expected, we find that the transverse structures of the quark-photon vertex lead to a suppression of the quark-loop contribution to the anomalous magnetic moment of the muon. However, we find evidence that this suppression is overestimated within models with simple approximations for the quark-photon interaction.