Basic features of nonstrange vector and axial vector mesons are analyzed in the framework of a chiral quark model that includes nonlocal four-fermion couplings. Unknown model parameters are determined from some input values of masses and decay constants, while nonlocal form factors are taken from a fit to lattice QCD results for effective quark propagators. Numerical results show a good agreement with the observed meson phenomenology.

We investigate whether the Balitsky-Fadin-Kuraev-Lipatov (BFKL) low $x$ evolution equation is capable to describe the energy dependence of the exclusive photo-production cross-section of vector mesons $J/\mathrm{\Psi }$ and $\mathrm{\Upsilon }$ on protons. Such cross-sections have been measured by both HERA experiments H1 and ZEUS in electron-proton collisions and by LHC experiments ALICE, CMS and LHCb in ultra-peripheral proton-proton and ultra-peripheral proton-lead collisions. Our approach provides a perturbative description of the rise with energy and relies only on a fit of the initial transverse momentum profile of the proton impact factor, which can be extracted from BFKL fits to inclusive HERA data. We find that BFKL evolution is capable to provide a very good description of the energy dependence of the current data set, while the available fits of the proton impact factor require an adjustment in the overall normalization.

The discovery of the baryonic states $P_c^{+}(4380)$ and $P_c^{+}(4450)$ by the LHCb collaboration in the process $pp\to b\overline{b}\to {\mathrm{\Lambda }}_b^{0}X$, followed by the decay ${\mathrm{\Lambda }}_b^0\to J/\psi p{K}^{-}$ has evoked a lot of theoretical interest. These states have the minimal quark content $c\overline{c}uud$, as suggested by their discovery mode $J/\psi p$, and the preferred $J^P$ assignments are ${\frac{5}{2}}^{+}$ for the $P_c^{+}(4450)$ and ${\frac{3}{2}}^{-}$ for the $P_c^{+}(4380)$. In the compact pentaquark hypothesis, in which they are interpreted as hidden charm diquark-diquark-antiquark baryons, the assigned spin and angular momentum quantum numbers are $P_c^{+}(4380)=\{\overline{c}[cu{]}_{s=1}[ud{]}_{s=1};L_{\mathcal{P}}=0,J^{\mathrm{P}}={\frac{3}{2}}^{-}\}$ and $P_c^{+}(4450)=\{\overline{c}[cu{]}_{s=1}[ud{]}_{s=0};L_{\mathcal{P}}=1,J^{\mathrm{P}}={\frac{5}{2}}^{+}\}$. The subscripts denote the spin of the diquarks and $L_{\mathcal{P}}=0$, 1 are the orbital angular momentum quantum numbers of the pentaquarks. We point out that in the heavy quark limit, the spin of the light diquark in heavy baryons becomes a good quantum number, which has consequences for the decay ${\mathrm{\Lambda }}_b^0\to J/\psi p{K}^{-}$. With the quantum numbers assigned above for the two pentaquarks, this would allow only the higher mass pentaquark state $P_c^{+}(4450)$ having $[ud{]}_{s=0}$ to be produced in ${\mathrm{\Lambda }}_b^0$ decays, whereas the lower mass state $P_c^{+}(4380)$ having $[ud{]}_{s=1}$ is disfavored, requiring a different interpretation. Pentaquark spectrum is rich enough to accommodate a $J^P={\frac{3}{2}}^{-}$ state, which has the correct light diquark spin $\{\overline{c}[cu{]}_{s=1}[ud{]}_{s=0};L_{\mathcal{P}}=0,J^{\mathrm{P}}={\frac{3}{2}}^{-}\}$ to be produced in ${\mathrm{\Lambda }}_b^0$ decays. Assuming that the mass difference between the charmed pentaquarks which differ in the orbital angular momentum $L$ by one unit is similar to the corresponding mass difference in the charmed baryons, $m[{\mathrm{\Lambda }}_c^{+}(2625);J^P={\frac{3}{2}}^{-}]-m[{\mathrm{\Lambda }}_c^{+}(2286);J^P={\frac{1}{2}}^{+}]\simeq 341\mathrm{MeV}$, we estimate the mass of the lower pentaquark $J^P=3/2^{-}$ state to be about 4110 MeV and suggest to reanalyze the LHCb data to search for this third state. Extending these considerations to the pentaquark states having a $c\overline{c}$ pair and three light quarks ($u$, $d$, $s$) in their Fock space, we present the spectroscopy of the $S$- and $P$-wave states in an effective Hamiltonian approach. Some of these pentaquarks can be produced in weak decays of the $b$-baryons. Combining heavy quark symmetry and the $SU(3{)}_F$ symmetry results in strikingly simple relations among the decay amplitudes which are presented here.

In view of the projected high number of produced $B$ mesons in the Belle II experiment ($\sim 10^{10}$ per year), in addition to the ongoing LHC-b, we calculate the rate of decay for the rare decays of $B$ mesons via a sterile on-shell neutrino $N$, which subsequently may decay leptonically or semileptonically within the detector: $B\to (D^{(*)}){\ell }_1^{\pm }N$, then $N\to {\ell }_1^{\pm }{\ell }_2^{\mp }\nu$ or $N\to {\ell }^{\pm }{\pi }^{\mp }$. Here, ${\ell }_1\ne {\ell }_2$ in order to avoid serious QED background. We account for the possible effects of the neutrino lifetime on the observability of the rare decays. If no charmed mesons [$D^{(*)}$] are produced at the first vertex of the sterile neutrino, a strong Cabibbo-Kobayashi-Maskawa (CKM) suppression becomes effective; this is not true if we consider instead the decays of $B_c$ mesons, which can be produced copiously in LHC-b. The production of charmed mesons $D^{(*)}$ at the first vertex offers an attractive possibility because it avoids strong CKM suppression. Such rare decays of $B$ mesons could be detected at the Belle II experiment, with the $N$ neutrino either decaying within the detector or manifesting itself as a massive missing momentum.

A search for Higgs-boson pair production in the $b\overline{b}b\overline{b}$ final state is carried out with $3.2{\mathrm{fb}}^{-1}$ of proton-proton collision data collected at $\sqrt{s}=13\mathrm{TeV}$ with the ATLAS detector. The data are consistent with the estimated background and are used to set upper limits on the production cross section of Higgs-boson pairs times branching ratio to $b\overline{b}b\overline{b}$ for both nonresonant and resonant production. In the case of resonant production of Kaluza-Klein gravitons within the Randall-Sundrum model, upper limits in the 24 to 91 fb range are obtained for masses between 600 and 3000 GeV, at the 95% confidence level. The production cross section times branching ratio for nonresonant Higgs-boson pairs is also constrained to be less than 1.22 pb, at the 95% confidence level.

A comprehensive study of the atmospheric neutrino flux in the energy region from sub-GeV up to several TeV using the Super-Kamiokande (SK) water Cherenkov detector is presented in this paper. The energy and azimuthal spectra, and variation over time, of the atmospheric ${\nu }_e+{\overline{\nu }}_e$ and ${\nu }_{\mu }+{\overline{\nu }}_{\mu }$ fluxes are measured. The energy spectra are obtained using an iterative unfolding method by combining various event topologies with differing energy responses. The azimuthal spectra depending on energy and zenith angle, and their modulation by geomagnetic effects, are also studied. A predicted east-west asymmetry is observed in both the ${\nu }_e$ and ${\nu }_{\mu }$ samples at $8.0\sigma$ and $6.0\sigma$ significance, respectively, and an indication that the asymmetry dipole angle changes depending on the zenith angle was seen at the $2.2\sigma$ level. The measured energy and azimuthal spectra are consistent with the current flux models within the estimated systematic uncertainties. A study of the long-term correlation between the atmospheric neutrino flux and the solar magnetic activity cycle is performed, and a weak preference for a correlation was seen at the $1.1\sigma$ level, using SK-I–SK-IV data spanning a 20-year period. For several particularly strong solar activity periods, corresponding to Forbush decrease events, no theoretical prediction is available but a deviation below the typical neutrino event rate is seen at the $2.4\sigma$ level. The seasonal modulation of the neutrino flux is also examined, but the change in flux at the SK site is predicted to be negligible, and, as expected, no evidence for a seasonal correlation is seen.

We analyze patterns of dynamical symmetry breaking in strongly coupled chiral gauge theories with direct-product gauge groups $G$. If the gauge coupling for a factor group $G_i\subset G$ becomes sufficiently strong, it can produce bilinear fermion condensates that break the $G_i$ symmetry itself and/or break other gauge symmetries $G_j\subset G$. Our comparative study of a number of strongly coupled direct-product chiral gauge theories elucidates how the patterns of symmetry breaking depend on the structure of $G$ and on the relative sizes of the gauge couplings corresponding to factor groups in the direct product.

In quantum field theory in curved backgrounds, one typically distinguishes between objective, tensorial quantities such as the renormalized stress-energy tensor (RSET) and subjective, nontensorial quantities such as Bogoliubov coefficients which encode perception effects associated with the specific trajectory of a detector. In this work, we propose a way to treat both objective and subjective notions on an equal tensorial footing. For that purpose, we define a new tensor which we will call the perception renormalized stress-energy tensor (PeRSET). The PeRSET is defined as the subtraction of the RSET corresponding to two different vacuum states. Based on this tensor, we can define perceived energy densities and fluxes. The PeRSET helps us to have a more organized and systematic understanding of various results in the literature regarding quantum field theory in black hole spacetimes. We illustrate the physics encoded in this tensor by working out various examples of special relevance.

We show that the horizon instability of the extremal Kerr black hole is associated with a singular branch point in the Green function at the superradiant bound frequency. We study generic initial data supported away from the horizon and find an enhanced growth rate due to nonaxisymmetric modes. The growth is controlled by the conformal weight $h$ of each mode. We speculate on connections to near-extremal black holes and holographic duality.

We consider electrovacuum black hole spacetimes in classical extensions of Eddington-inspired Born-Infeld gravity. By rewriting the Born-Infeld action as the square root of the determinant of a matrix $\widehat{\mathrm{\Omega }}$, we consider the family of models $f(|\widehat{\mathrm{\Omega }}|)$ and study black hole solutions for a power-law family of models labeled by a simple parameter. We show how the innermost structure of the corresponding black holes is modified as compared to their general relativity counterparts, discussing in which cases a wormhole structure replaces the pointlike singularity. We go forward to argue that in such cases a geodesically complete and, thus, nonsingular spacetime is present, despite the existence of curvature divergences at the wormhole throat.

We show that a massless canonical scalar field minimally coupled to general relativity can become a tachyonic ghost at low energies around a background in which the scalar’s gradient is spacelike. By performing a canonical transformation we demonstrate that this low energy ghost can be recast, at the level of the action, in a form of a fluid that undergoes a Jeans-like instability affecting only modes with large wavelength. This illustrates that low energy tachyonic ghosts do not lead to a catastrophic quantum vacuum instability, unlike the usual high-energy ghost degrees of freedom.

We study a one-loop induced radiative neutrino model with an inert isospin triplet scalar field in the general framework of $U(1{)}_Y$, in which we discuss current neutrino oscillation data, lepton flavor violations, a muon anomalous magnetic moment, and a dark matter candidate depending on the number of hypercharges. We show global analysis combining all the constraints and discuss the model.

Searches for new hadronic resonances typically focus on high-mass spectra due to overwhelming QCD backgrounds and detector trigger rates. We present a study of searches for relatively low-mass hadronic resonances at the LHC in the case that the resonance is boosted by recoiling against a well-measured high-$p_{\mathrm{T}}$ probe such as a muon, photon or jet. The hadronic decay of the resonance is then reconstructed either as a single large-radius jet or as a resolved pair of standard narrow-radius jets, balanced in transverse momentum to the probe. We show that the existing 2015 LHC data set of $pp$ collisions with $\int \mathcal{L}dt=4{\mathrm{fb}}^{-1}$ should already have powerful sensitivity to a generic $Z^{\prime }$ model which couples only to quarks, for $Z^{\prime }$ masses ranging from $20–500\mathrm{GeV}/{\mathrm{c}}^2$.

Based on the truncated Dyson-Schwinger equations for the fermion propagator with $N$ fermion flavors at zero temperature, the chiral phase transition of quantum electrodynamics in $2+1$ dimensions (${\mathrm{QED}}_3$) with boson mass—which is obtained via the Anderson-Higgs mechanism—is investigated. In the chiral limit, we find that the critical behavior of ${\mathrm{QED}}_3$ with a massless boson is different from that with a massive boson: the chiral phase transition in the presence of a nonzero boson mass reveals the typical second-order phase transition, at either the critical boson mass or a critical number of fermion flavors, while for a vanishing boson mass it exhibits a higher than second-order phase transition at the critical number of fermion flavors. Furthermore, it is shown that the system undergoes a crossover behavior from a small number of fermion flavors or boson mass to its larger one beyond the chiral limit.

Spherical vacuum and scalar collapse for the Starobinsky $R^2$ model is simulated. Obtained by considering the quantum-gravitational effects, this model would admit some cases of singularity-free cosmological spacetimes. It is found, however, that in vacuum and scalar collapse, when $f^{\prime }$ or the physical scalar field is strong enough, a black hole including a central singularity can be formed. In addition, near the central singularity, gravity dominates the repulsion from the potential, so that in some circumstances the Ricci scalar is pushed to infinity by gravity. Therefore, the semiclassical effects as included here do not avoid the singularity problem in general relativity. A strong physical scalar field can prevent the Ricci scalar from growing to infinity. Vacuum collapse for the $R\ln R$ model is explored, and it is observed that for this model the Ricci scalar can also go to infinity as the central singularity is approached. Therefore, this feature seems universal in vacuum and scalar collapse in $f(R)$ gravity.

We study axionic inflation with a modulated potential and examine if the primordial tensor power spectrum exhibits oscillatory feature, which is testable with future space-based gravitational-wave experiments such as DECIGO and BBO. In the case of single-field axion monodromy inflation, it turns out that it is difficult to detect an oscillation in the spectrum due to the suppression of the sub-Planckian decay constant of the axion. On the other hand, in the case of aligned chromo-natural inflation where the axion is coupled to a SU(2) gauge field, it turns out that a sizable oscillation in the tensor spectrum can occur due to the enhancement of chiral gravitational waves sourced by the gauge field. We expect that this feature will be a new probe for axion phenomenologies in the early Universe through chiral gravitational waves.

We investigate if the hemispherical asymmetry in the CMB is produced from “asymmetric” excited initial conditions. We show that in the limit where the deviations from the Bunch-Davies vacuum are large and the scale of new physics is maximally separated from the inflationary Hubble parameter, the primordial power spectrum is modulated only by position-dependent dipole and quadrupole terms. Requiring the dipole contribution in the power spectrum to account for the observed power asymmetry, $A=0.07\pm 0.022$, we show that the amount of quadrupole terms is roughly equal to $A^2$. The mean local bispectrum, which gets enhanced for the excited initial state, is within the $1\sigma$ bound of Planck 2015 results for a large field model, $f_{\mathrm{NL}}\simeq 4.17$, but is reachable by future CMB experiments. The amplitude of the local non-Gaussianity modulates around this mean value, depending on the angle that the correlated patches on the 2d CMB surface make with the preferred direction. The amount of variation is minimized for the configuration in which the short and long wavelength modes are around the preferred pole and $|{\overrightarrow{k}}_3|\approx |{\overrightarrow{k}}_{l\approx 10}|\ll |{\overrightarrow{k}}_1|\approx |{\overrightarrow{k}}_2|\approx |{\overrightarrow{k}}_{l\approx 2500}|$ with $f_{\mathrm{NL}}^{\min }\approx 3.64$. The maximum occurs when these modes are at the antipode of the preferred pole, $f_{\mathrm{NL}}^{\max }\approx 4.81$. The difference of non-Gaussianity between these two configurations is as large as $\simeq 1.17$, which can be used to distinguish this scenario from other scenarios that try to explain the observed hemispherical asymmetry.

Based on the results of the classification by T.-h. Abe et al., Nucl. Phys. B894, 374 (2015)., we exhaustively investigate Yukawa sector of $U(8)$ model on magnetized orbifolds $T^2/Z_2$, $T^2/Z_3$, $T^2/Z_4$ and $T^2/Z_6$ by evaluating ratios of the mass eigenvalues of the three states in all the possible configurations with one and two Higgs pairs where three generations are realized in fermions. Because of the smearing effect via kinetic mixing, one can realize a hierarchy such as ${10}^{-2}–{10}^{-3}$, but it is very difficult to achieve the mass ratio between the up and top quarks ($m_{\text{up}}/m_{\text{top}}\sim {10}^{-5}$) on the complicated magnetized orbifolds $T^2/Z_N(N=3,4,6)$.

We explore new physics (NP) effects in Higgs-vector boson associated production at a future International Linear Collider (ILC) via $e^{+}{e}^{-}\to Zh,Zhh$, using effective field theory (EFT) techniques. In particular, we focus on a certain class of dimension 6 operators, which are generated by tree-level exchanges of a new heavy vector field in the underlying theory. These operators induce new contact terms of the form $\psi \psi \varphi D\varphi$, involving the Standard Model (SM) fermions ($\psi$), gauge-bosons ($D$ is the covariant derivative) and the SM Higgs field ($\varphi$). We investigate the high-energy behavior of these new effective interactions in $e^{+}{e}^{-}\to Zh,Zhh$, imposing bounds from electroweak precision measurements, and show that the ILC is an excellent testing ground for probing this type of NP via $e^{+}{e}^{-}\to Zh,Zhh$. We also address the validity of the EFT expansion and we study the correlation between the $hZ$ and $hhZ$ signals, which can be utilized in future searches for NP in these channels.