A salient feature shared by all tetraquark candidates observed in experiment is the absence of flavor-exotic states of the type $\overline{a}b\overline{c}d$, with four different quark flavors. This phenomenon may be understood from the properties of large-$N_c$ QCD. On the one hand, previous work shows that consistency conditions for flavor-exotic Green functions, potentially containing these tetraquark poles, require the existence of two tetraquarks $T_A$ and $T_B$: Each of them should decay dominantly via a single two-meson channel, $T_A\to M_{\overline{a}b}{M}_{\overline{c}d}$ and $T_B\to M_{\overline{a}d}{M}_{\overline{c}b}$, with suppressed rates $T_A\to M_{\overline{a}d}{M}_{\overline{c}b}$ and $T_B\to M_{\overline{a}b}{M}_{\overline{c}d}$. On the other hand, we have at hand only one diquark-antidiquark flavor structure $(\overline{a}\overline{c})(bd)$ that might produce a compact tetraquark bound state. Taking into account that the diquark-antidiquark structure is the only viable candidate for a compact tetraquark state, one concludes that it is impossible to obtain two different narrow tetraquarks decaying dominantly into distinct two-meson channels. This contradiction suggests that large-$N_c$ QCD does not support the existence of narrow flavor-exotic tetraquarks. This argument does not rule out the possible existence of broad molecular-type flavor-exotic states or of molecular-type bound states lying very close to the two-meson thresholds.

Cold nuclear matter effects in reactions with nuclei at a future electron-ion collider (EIC) lead to a modification of semi-inclusive hadron production, jet cross sections, and jet substructure when compared to the vacuum. At leading order in the strong coupling, a jet produced at an EIC is initiated as an energetic quark, and the process of this quark splitting into a quark-gluon system underlies experimental observables. The spectrum of gluons associated with the branching of this quark jet is heavily modified by multiple scattering in a medium, allowing jet cross sections and jet substructure to be used as a probe of the medium’s properties. We present a formalism that allows us to compute the gluon spectrum of a quark jet to an arbitrary order in opacity, the average number of scatterings in the medium. This calculation goes beyond the simplifying limit in which the gluon radiation is soft and can be interpreted as energy loss of the quark, and it significantly extends previous work which computes the full gluon spectrum only to first order in opacity. The theoretical framework demonstrated here applies equally well to light parton and heavy quark branching, and is easily generalizable to all in-medium splitting processes.

Recent work by Block et al. on the energy-invariant edge in proton-proton scattering is interpreted by quantitatively introducing an energy-dependent black-disk fraction of the proton-proton interaction.

We compute the $\mathrm{QCD}\times \mathrm{QED}$ [$\mathcal{O}({\alpha }_s\alpha )$] mixed and ${\mathrm{QED}}^2$ [$\mathcal{O}({\alpha }^2)$] corrections to the production of an on-shell $Z$ boson in hadronic collisions. We obtain them by profiting from the calculation of the pure QCD terms after taking the corresponding Abelian limits. Therefore, we extend the available knowledge up to complete next-to-next-to-leading-order precision in $\mathrm{QCD}\oplus \mathrm{QED}$. We present explicit results for the perturbative coefficients and perform the phenomenological analysis at different collider energies with particular emphasis on the mixed corrections. We study the contribution from the different channels and discuss the scale dependence stabilization effect. We find that the contributions compete with the pure QCD NNLO ones under relevant kinematical conditions for the LHC, despite the fact that they are small, typically at the few per mille level.

We study the $\gamma p\to p{f}_0$ [$f_0(980)$ and $f_0(1500)$] reaction close to threshold within an effective Lagrangian approach. The production process is described by an $s$-channel nucleon pole or $t$-channel $\rho$ and $\omega$ exchange. The $K^0{\overline{K}}^0$ invariant mass distributions of the $\gamma p\to f_0(980)p\to K^0{\overline{K}}^0$ and $\gamma p\to f_0(1500)p\to K^0{\overline{K}}^{0}p$ reactions are investigated, where the two kaons have been separated in the $S$ wave decaying from $f_0(980)$ and $f_0(1500)$. It is shown that the $s$-channel process is favored for the production of $f_0(980)$, while for the $f_0(1500)$ production, the experimental measurements can be described quite well by the $t$-channel process. It is expected that the theoretical results can be tested by further experiments at CLAS.

The measured electromagnetic form factors of $\mathrm{\Lambda }$ hyperon in the timelike region are significantly deviated from pQCD prediction. We attribute the nonvanishing cross section near threshold to be the contribution of below-threshold $\varphi (2170)$ state, supporting its exotic structure. Above the threshold, we find significant role of a wide vector meson with the mass of around 2.34 GeV, which would be the same state present in $p\overline{p}$ annihilation reactions. As a result, we give a satisfactory description of the behavior of existing data without modifying pQCD expectation.

The Higgs self-interactions play a crucial role in exploring the underlying mechanisms of electroweak symmetry breaking and the nature of the phase transition involved. In this article, we propose to probe the quartic Higgs self-interaction at lepton and hadron colliders, via the di-Higgs productions. We analyze the contributions of the quartic Higgs coupling, including the renormalization of the cubic Higgs coupling and the modification of the $VVhh$ form factor, to the vector boson–fusion and the vector boson–associated di-Higgs productions at one-loop level. Such an effect is independent of the choice of gauge fixing, if the quartic Higgs coupling is decoupled from other couplings in the contexts considered. Notably, a combination of these two di-Higgs productions is important for optimizing the collider sensitivities to probe the quartic Higgs coupling. With this guideline, we explore the International Linear Collider and Compact Linear Collider sensitivities, and find that the International Linear Collider has the potential to measure the quartic Higgs coupling, normalized by its standard model value, with a precision of $\sim \pm 25$ (500 GeV, $4{\mathrm{ab}}^{-1}+1\mathrm{TeV}$, $2.5{\mathrm{ab}}^{-1}$) and $\sim \pm 20$ (500 GeV, $4{\mathrm{ab}}^{-1}+1\mathrm{TeV}$, $8{\mathrm{ab}}^{-1}$), at $1\sigma \mathrm{C}.\mathrm{L}.$, after marginalizing the cubic Higgs coupling in the ${\chi }^2$ analysis. The dependence on the renormalization scheme of the cubic Higgs coupling is discussed.

The double-beta decay of ${}^{116}\mathrm{Cd}$ has been investigated with the help of radiopure enriched ${}^{116}\mathrm{Cd}{\mathrm{WO}}_4$ crystal scintillators (mass of 1.162 kg) at the Gran Sasso underground laboratory. The half-life of ${}^{116}\mathrm{Cd}$ relative to the $2\nu 2\beta$ decay to the ground state of ${}^{116}\mathrm{Sn}$ was measured with the highest up-to-date accuracy as $T_{1/2}=(2.63_{-0.12}^{+0.11})\times {10}^{19}\mathrm{yr}$. A new improved limit on the $0\nu 2\beta$ decay of ${}^{116}\mathrm{Cd}$ to the ground state of ${}^{116}\mathrm{Sn}$ was set as $T_{1/2}\ge 2.2\times {10}^{23}\mathrm{yr}$ at 90% C.L., which is the most stringent known restriction for this isotope. It corresponds to the effective Majorana neutrino mass limit in the range $⟨m_{\nu }⟩\le (1.0–1.7)\mathrm{eV}$, depending on the nuclear matrix elements used in the estimations. New improved half-life limits for the $0\nu 2\beta$ decay with majoron(s) emission, Lorentz-violating $2\nu 2\beta$ decay, and $2\beta$ transitions to excited states of ${}^{116}\mathrm{Sn}$ were set at the level of $T_{1/2}\ge {10}^{20}–{10}^{22}\mathrm{yr}$. New limits for the hypothetical lepton-number violating parameters (right-handed currents admixtures in weak interaction, the effective majoron-neutrino coupling constants, R-parity violating parameter, Lorentz-violating parameter, heavy neutrino mass) were set.

We present state-of-the-art results for the matrix elements of flavor diagonal tensor operators within the nucleon state. The calculation of the dominant connected contribution is done using 11 ensembles of gauge configurations generated by the MILC Collaboration using the highly improved staggered quark action with $2+1+1$ dynamical flavors. The calculation of the disconnected contributions is done using seven (six) ensembles for the strange (light) quarks. These high-statistics simulations allowed us to address various systematic uncertainties. A simultaneous fit in the lattice spacing and the light-quark mass is used to extract the tensor charges in the continuum limit and at $M_{\pi }=135\mathrm{MeV}$. Results for the proton in the $\overline{\mathrm{MS}}$ scheme at 2 GeV are $g_T^u=0.784(28)(10)$, $g_T^d=-0.204(11)(10)$ and $g_T^s=-0.0027(16)$. Implications of these results for constraining the quark electric dipole moments and their contributions to the neutron electric dipole moment are discussed.

We study the chiral symmetry breaking and restoration in ($2+1$)-dimensional gauge theories from the holographic hardwall and softwall models. We describe the behavior of the chiral condensate in the presence of an external magnetic field for both models at finite temperature. For the hardwall model we find magnetic catalysis (MC) in different setups. For the softwall model we find inverse magnetic catalysis (IMC) and MC in different situations. We also find for the softwall model a crossover transition from IMC to MC at a pseudocritical magnetic field. This study also shows spontaneous symmetry breaking for both models. Interestingly, for $B=0$ in the softwall model, we found a nontrivial expectation value for the chiral condensate.

A recent experiment [J. L. Garrett, D. A. T. Somers, and J. N. Munday, Phys. Rev. Lett 120, 040401 (2018)] measured for the first time the gradient of the Casimir force between two gold spheres in vacuum at room temperature, and placed a bound on the magnitude of the deviation of the measured force from the proximity force approximation (PFA). The present work extends a previous theoretical analysis of this experiment [G. Bimonte, Phys. Rev. D 97, 085011 (2018)], by analyzing in detail how the magnitude of the deviation from PFA is affected by the inclusion or neglect of ohmic dissipation at zero frequency, a much debated issue in the current Casimir literature, which goes by the name of the Drude vs plasma controversy. We analyze as well the effect of connecting the conductors to charge reservoirs, which is the standard configuration used in Casimir experiments. We describe a simple and effective decimation procedure, allowing for a faster computation of the Casimir force for large aspect ratios of the system.

It has been argued that black hole solutions become unavoidably time-dependent when the graviton has a mass. In this work we show that, if the apparent horizon of the black hole is a null surface with respect to a fiducial Minkowski reference metric, then there is a natural sense in which the location of the horizon is necessarily time-independent, despite the dynamical metric possessing no time-like Killing vector. We derive a second law of black hole mechanics for these black holes and determine their surface gravity. An additional assumption establishes a zeroth and a first law of black hole mechanics. These results are nonperturbative and model-independent. We apply these results to the specific model of dRGT ghost-free massive gravity and show that consistent solutions exist which obey the required assumptions. We determine the time-dependent scalar curvature at the horizon of these black holes.

It was recently shown that strong cosmic censorship may be violated in highly charged black-hole spacetimes living in a universe with a positive cosmological constant. Several follow-up works have since suggested that such a result, while conceptually interesting, cannot be upheld in practice. We focus here on the claim that the presence of charged massive scalars suffices to save strong cosmic censorship. To the contrary, we show that there still exists a finite region in parameter space where strong cosmic censorship is expected to be violated.

The field of a massive vector boson in the vicinity of a rotating black hole is known to suffer an instability, due to the exponential amplification of (corotating, low-frequency) bound state modes by black hole superradiance. Here we calculate the bound state spectrum by exploiting the separation of variables recently achieved by Frolov, Krtouš, Kubizňák and Santos (FKKS) for the Proca field on Kerr-(A)dS-NUT spacetimes of arbitrary dimension. Restricting to the 4D Kerr case, we first establish the relationship between the FKKS and Teukolsky variables in the massless case; obtain exact results for the angular eigenvalues in the marginally-bound case; and present a spectral method for solving the angular equation in the general case. We then demonstrate that all three physical polarizations can be recovered from the FKKS ansatz, resolving an open question. We present numerical results for the instability growth rate for a selection of modes of all three polarizations, and discuss physical implications.

As current gravitational wave (GW) detectors increase in sensitivity, and particularly as new instruments are being planned, there is the possibility that ground-based GW detectors will observe GWs from highly eccentric neutron star binaries. We present the first detailed study of highly eccentric BNS systems with full $(3+1)\mathrm{D}$ numerical relativity simulations using consistent initial conditions, i.e., setups which are in agreement with the Einstein equations and with the equations of general relativistic hydrodynamics in equilibrium. Overall, our simulations cover two different equations of state (EOSs), two different spin configurations, and three to four different initial eccentricities for each pairing of EOS and spin. We extract from the simulated waveforms the frequency of the $f$-mode oscillations induced during close encounters before the merger of the two stars. The extracted frequency is in good agreement with $f$-mode oscillations of individual stars for the irrotational cases, which allows an independent measure of the supranuclear equation of state not accessible for binaries on quasicircular orbits. The energy stored in these $f$-mode oscillations can be as large as ${10}^{-3}{M}_{\odot }\sim {10}^{51}\mathrm{erg}$, even with a soft EOS. In order to estimate the stored energy, we also examine the effects of mode mixing due to the stars’ offset from the origin on the $f$-mode contribution to the GW signal. While in general (eccentric) neutron star mergers produce bright electromagnetic counterparts, we find that for the considered cases with fixed initial separation the luminosity decreases when the eccentricity becomes too large, due to a decrease of the ejecta mass. Finally, the use of consistent initial configurations also allows us to produce high-quality waveforms for different eccentricities which can be used as a test bed for waveform model development of highly eccentric binary neutron star systems.

With a decade of $\gamma$-ray data from the Fermi-LAT telescope, we can now hope to answer how well we understand the local Universe at $\gamma$-ray frequencies. On the other hand, with $\gamma$-ray data alone it is not possible to directly access the distance of the emission and to point out the origin of unresolved sources. This obstacle can be overcome by cross-correlating the $\gamma$-ray data with catalogs of objects with well-determined redshifts and positions. In this work, we cross-correlate Fermi-LAT skymaps with the 2MPZ catalog to study the local $z<0.2$ $\gamma$-ray Universe, where about 10% of the total unresolved $\gamma$-ray background is produced. We find the signal to be dominated by AGN emissions, while star forming galaxies provide a subdominant contribution. Possible hints for a particle DM signal are discussed.

We explore signals of lepton-number-violation in the charm physics sector. We study the four-body $|\mathrm{\Delta }L|=2$ decays of the $D^0$ meson, $D^0\to P^{-}{\pi }^{-}{\mu }^{+}{\mu }^{+}$ ($P=\pi$, $K$) as an alternative evidence of the Majorana nature of neutrinos. We carry out an exploratory study on the potential sensitivity that LHCb experiment could achieve for these $|\mathrm{\Delta }L|=2$ processes. We show that for a long term expected integrated luminosity of $300{\mathrm{fb}}^{-1}$, a signal significance of branching ratios of the order $\mathcal{O}({10}^{-9})$ might be accessible, allowing to improve the experimental bounds obtained by the E791 experiment. Limits on the parameter space of a heavy sterile neutrino that could be obtained from their experimental search are discussed as well.

We introduce a new method for calculating the $\mathrm{O}({\alpha }^3)$ hadronic-vacuum-polarization contribution to the muon anomalous magnetic moment from ab initio lattice QCD. We first derive expressions suitable for computing the higher-order contributions either from the renormalized vacuum polarization function $\widehat{\mathrm{\Pi }}(q^2)$ or directly from the lattice vector-current correlator in Euclidean space. We then demonstrate the approach using previously published results for the Taylor coefficients of $\widehat{\mathrm{\Pi }}(q^2)$ that were obtained on four-flavor QCD gauge-field configurations with physical light-quark masses. We obtain ${10}^{10}{a}_{\mu }^{\mathrm{HVP},\mathrm{HO}}=-9.3(1.3)$ in agreement with, but with a larger uncertainty than, determinations from $e^{+}{e}^{-}\to \text{hadrons}$ data plus dispersion relations.

We discuss how to apply the Hessian method (i) to predict the impact of a new data set (or sets) on the parton distribution functions (PDFs) and their errors, by producing an updated best-fit PDF and error PDF sets, such as the CTEQ-TEA PDFs; (ii) to predict directly the effect of a new data set on the PDF errors of any other set of observables, without the need to recalculate using the new error PDFs; and (iii) to transform the original set into a reduced set of error PDFs which is optimized for a specific set of observables to reproduce the PDF-induced uncertainties to any specified precision. We present a software package, ePump (Error PDF Updating Method Package), that can be used to update or optimize a set of PDFs, including the best-fit PDF set and Hessian eigenvector pairs of PDF sets (i.e., error PDFs), and to update any other set of observables. We demonstrate the potential of the program by presenting selected phenomenological applications relevant to the Large Hadron Collider. Special care is given to discuss the assumptions made and the limitations of this theoretical framework compared to a treatment by the full global-analysis program.