We assess current experimental constraints on the $\text{bidoublet}+\text{singlet}$ model of top compositeness previously proposed in the literature. This model extends the Standard Model’s spectrum by adding a custodially embedded vectorlike electroweak bidoublet of quarks and a vectorlike electroweak singlet quark. While either of those states alone would produce a model in tension with constraints from precision electroweak data, in combination they can produce a viable model. We show that current precision electroweak data, in the wake of the Higgs discovery, accommodate the model and we explore the impact of direct collider searches for the partners of the top quark.

We study the purely leptonic decays of $W^{\pm }\to e^{\pm }{e}^{\pm }{\mu }^{\mp }\nu$ and ${\mu }^{\pm }{\mu }^{\pm }{e}^{\mp }\nu$ produced at the LHC, induced by sterile neutrinos with mass $m_N$ below $M_W$ in the intermediate state. Since the final state neutrino escapes detection, one cannot tell whether this process violates lepton number, which would indicate a Majorana character for the intermediate sterile neutrino. Our study shows that when the sterile neutrino mixings with electrons and muons are different enough, one can still discriminate between the Dirac and Majorana character of this intermediate neutrino by simply counting and comparing the above decay rates. After performing collider simulations and statistical analysis, we find that at the 14 TeV LHC with an integrated luminosity of $3000{\mathrm{fb}}^{-1}$, for two benchmark scenarios $m_N=20$ and 50 GeV, at least a $3\sigma$ level of exclusion on the Dirac case can be achieved for disparities as mild as, e.g., $|U_{Ne}{|}^2<0.7|U_{N\mu }{|}^2$ or $|U_{N\mu }{|}^2<0.7|U_{Ne}{|}^2$, provided that $|U_{Ne}{|}^2$ and $|U_{N\mu }{|}^2$ are both above $\sim 2\times {10}^{-6}$.

Vector leptoquarks provide an elegant solution to a series of anomalies and at the same time generate naturally light neutrino masses through their mixing with the standard model Higgs boson. We present a simple Froggatt-Nielsen model to accommodate the $B$ physics anomalies $R_K$ and $R_D$, neutrino masses, and the 750 GeV diphoton excess in one cohesive framework adding only two vector leptoquarks and two singlet scalar fields to the standard model field content.

We present the first calculation of the one-loop corrections to the triple Higgs coupling in the framework of a simplified $3+1$ Dirac neutrino model, that is three light neutrinos plus one heavy neutrino embedded in the Standard Model (SM). The triple Higgs coupling is a key parameter of the scalar potential triggering the electroweak symmetry-breaking mechanism in the SM. The impact of the heavy neutrino can be as large as $+20\%$ to $+30\%$ for parameter points allowed by the current experimental constraints depending on the tightness of the perturbative bound. This can be probed at the high-luminosity LHC, at future electron-positron colliders and at the Future Circular Collider in hadron-hadron mode, an envisioned 100 TeV $pp$ machine. Our calculation, being done in the mass basis, can be extended to any model using the neutrino portal. In addition, the effects that we have calculated are expected to be enhanced if additional heavy fermions with large Yukawa couplings are included, as in low-scale seesaw mechanisms.

Color-octet bosons are a universal prediction of models in which the 750 GeV diphoton resonance corresponds to a pion of a QCD-like composite sector. We show that the existing searches for dijet and photon plus jet resonances at the LHC constrain single productions of color-octet states and can be translated into stringent limits on the 750 GeV diphoton rate. For a minimal $5+\overline{5}$ model, the 750 GeV diphoton signal cross section at the 13 TeV LHC is constrained to be below around 6 fb. Future LHC searches for dijet and photon plus jet resonances can establish evidence of a new color-octet state with $20{\mathrm{fb}}^{-1}$ and validate a pionlike explanation for the 750 GeV resonance.

The dependence on centrality, or on the number of nucleon participants, of the midrapidity density of charged particles measured in heavy-ion collisions at the collision energy of about 20 GeV at RHIC to the highest LHC energy of 5 TeV is investigated within the recently proposed effective-energy approach. This approach relates multihadron production in different types of collisions by combining, under the proper scaling of the collision energy, the constituent quark picture with Landau relativistic hydrodynamics. The measurements are shown to be well described based on the similarity of multihadron production process in (anti)proton-proton interactions and heavy-ion collisions driven by the centrality-dependent effective energy of participants.

It has been recently pointed out that a momentum-dependent coupling of the asymmetric dark matter (ADM) with nucleons can explain the broad disagreement between helioseismological observables and the predictions of standard solar models. In this paper, we propose a minimal simplified ADM model consisting of a scalar and a pseudoscalar mediator, in addition to a Dirac fermionic DM, for generating such momentum-dependent interactions. Remarkably, the pseudoscalar with mass around 750 GeV can simultaneously explain the solar anomaly and the recent diphoton excess observed by both ATLAS and CMS experiments in the early $\sqrt{s}=13\mathrm{TeV}$ LHC data. In this framework, the total width of the resonance is naturally large, as suggested by the ATLAS experiment, since the resonance mostly decays to the ADM pair. The model predicts the existence of a new light scalar in the GeV range, interacting with quarks, and observable dijet, monojet, and $t\overline{t}$ signatures for the 750 GeV resonance at the LHC.

We consider the possibility that the massive graviton is a viable candidate for dark matter in the context of bimetric gravity. We first derive the energy-momentum tensor of the massive graviton and show that it indeed behaves as that of dark matter fluid. We then discuss a production mechanism and the present abundance of massive gravitons as dark matter. Since the metric to which ordinary matter fields couple is a linear combination of the two mass eigenstates of bigravity, production of massive gravitons, i.e., the dark matter particles, is inevitably accompanied by generation of massless gravitons, i.e., the gravitational waves. Therefore, in this scenario some information about dark matter in our Universe is encoded in gravitational waves. For instance, if LIGO detects gravitational waves generated by the preheating after inflation, then the massive graviton with the mass of $\sim 0.01\mathrm{GeV}$ is a candidate for dark matter.

In this paper, we propose a novel powerful strategy to perform searches for new electroweak states. Uncolored electroweak states appear in generic extensions of the Standard Model (SM) and yet are challenging to discover at hadron colliders. This problem is particularly acute when the lightest state in the electroweak multiplet is neutral and all multiplet components are approximately degenerate. In this scenario, production of the charged fields of the multiplet is followed by decay into nearly invisible states; if this decay occurs promptly, the only way to infer the presence of the reaction is through its missing energy signature. Our proposal relies on emission of photon radiation from the new charged states as a means of discriminating the signal from SM backgrounds. We demonstrate its broad applicability by studying two examples: a pure Higgsino doublet and an electroweak quintuplet field.

We study the weak interaction axial form factors of the octet baryons, within the covariant spectator quark model, focusing on the dependence of four-momentum transfer squared, $Q^2$. In our model the axial form factors $G_A(Q^2)$ (axial-vector form factor) and $G_P(Q^2)$ (induced pseudoscalar form factor) are calculated based on the constituent quark axial form factors and the octet baryon wave functions. The quark axial current is parametrized by the two constituent quark form factors, the axial-vector form factor $g_A^q(Q^2)$, and the induced pseudoscalar form factor $g_P^q(Q^2)$. The baryon wave functions are composed of a dominant $S$-state and a $P$-state mixture for the relative angular momentum of the quarks. First, we study in detail the nucleon case. We assume that the quark axial-vector form factor $g_A^q(Q^2)$ has the same function form as that of the quark electromagnetic isovector form factor. The remaining parameters of the model, the $P$-state mixture and the $Q^2$ dependence of $g_P^q(Q^2)$, are determined by a fit to the nucleon axial form factor data obtained by lattice QCD simulations with large pion masses. In this lattice QCD regime the meson cloud effects are small, and the physics associated with the valence quarks can be better calibrated. Once the valence quark model is calibrated, we extend the model to the physical regime and use the low $Q^2$ experimental data to estimate the meson cloud contributions for $G_A(Q^2)$ and $G_P(Q^2)$. Using the calibrated quark axial form factors and the generalization of the nucleon wave function for the other octet baryon members, we make predictions for all the possible weak interaction axial form factors $G_A(Q^2)$ and $G_P(Q^2)$ of the octet baryons. The results are compared with the corresponding experimental data for $G_A(0)$ and with the estimates of baryon-meson models based on $SU(6)$ symmetry.

Warped extra dimensions can address both the Planck-weak and flavor hierarchies of the Standard Model (SM). In this paper we discuss the SM neutrino mass generation in a scenario in which a SM singlet bulk fermion—coupled to the Higgs and the lepton doublet near the IR brane—is given a Majorana mass of order the Planck scale on the UV brane. Despite the resemblance to a type I seesaw mechanism, a careful investigation based on the mass basis for the singlet four-dimensional modes reveals a very different picture. Namely, the SM neutrino masses are generated dominantly by the exchange of the TeV-scale mass eigenstates of the singlet, that are pseudo-Dirac and have a sizable Higgs-induced mixing with the SM doublet neutrino; remarkably, in warped five-dimensional (5D) models the anticipated type I seesaw morphs into a natural realization of the so-called “inverse” seesaw. This understanding uncovers an intriguing and direct link between neutrino mass generation (and possibly leptogenesis) and TeV-scale physics. We also perform estimates using the dual conformal field theory picture of our framework, which back up our 5D calculation.

Much attention has been paid to the quantum structure of the vacuum. Higher order processes in quantum electrodynamics are strongly believed to cause polarization and even breakdown of the vacuum in the presence of strong fields soon to be accessible in high intensity laser experiments. Less explored consequences of strong field electrodynamics include effects from Born-Infeld type of electromagnetic theories, a nonlinear electrodynamics that follows from classical considerations as opposed to coupling to virtual fluctuations. In this article, I will demonstrate how vacuum four wave mixing has the possibility to differentiate between these two types of vacuum responses: quantum effects on one hand and nonlinear classical extensions on the other.

We propose a definition of mass for characteristic hypersurfaces in asymptotically vacuum space-times with nonvanishing cosmological constant $\mathrm{\Lambda }\in {\mathbb{R}}^{*}$, generalizing the definition of Trautman and Bondi for $\mathrm{\Lambda }=0$. We show that our definition reduces to some standard definitions in several situations. We establish a balance formula linking the characteristic mass and a suitably defined renormalized volume of the null hypersurface, generalizing the positivity identity proved by Chruściel and Paetz when $\mathrm{\Lambda }=0$.

We provide a unified description of the flip-flop and the antialignment instability effects in spinning black hole binaries in terms of real and imaginary flip-flop frequencies. We find that this instability is only effective for mass ratios $0.5<q<1$. We find analytic expressions that determine the region of parameter space for which the instability occurs in terms of maps of the spin magnitudes and mass ratio $({\alpha }_1,{\alpha }_2;q)$. This restricts the priors of parameter estimation techniques for the observation of gravitational waves from quasialigned spinning binary black holes and it is relevant for their astrophysical modeling and final recoil computations.

The symmetries of unimodular gravity are clarified somewhat.

We study the localized direct $CP$ violation in the hadronic decays $B^{\pm }\to {\rho }^0(\omega ){\pi }^{\pm }\to {\pi }^{+}{\pi }^{-}{\pi }^{\pm }$, including the effect caused by an interesting mechanism involving the charge symmetry violating mixing between ${\rho }^0$ and $\omega$ in the QCD factorization approach. We find that $\rho \text{−}\omega$ mixing makes the localized integrated $CP$ asymmetry move toward the negative direction when the low invariant mass of ${\pi }^{+}{\pi }^{-}$ [$m({\pi }^{+}{\pi }^{-}{)}_{\mathrm{low}}$] is near ${\rho }^0(770)$. The localized integrated direct $CP$ violation obtained in the QCD factorization approach varies from $-0.0724$ to $-0.0389$ in the ranges of parameters when $0.750<m({\pi }^{+}{\pi }^{-}{)}_{\mathrm{low}}<0.800\mathrm{GeV}$. This result, especially the sign, agrees with the experimental data. We also calculate the localized integrated direct $CP$ violating asymmetries in the QCD factorization approach in the regions $0.470<m({\pi }^{+}{\pi }^{-}{)}_{\mathrm{low}}<0.770\mathrm{GeV}$ and $0.770<m({\pi }^{+}{\pi }^{-}{)}_{\mathrm{low}}<0.920\mathrm{GeV}$. We find that these results agree with the experimental data and are more accurate than the results obtained through the naive factorization approach. It is more clear that $\rho \text{−}\omega$ mixing contributes to the sign change in these two regions.

We extend the relaxation mechanism to the elementary Goldstone Higgs framework. Besides studying the allowed parameter space of the theory, we add the minimal ingredients needed for the framework to be phenomenologically viable. The very nature of the extended Higgs sector allows to consider very flat scalar potential directions along which the relaxation mechanism can be implemented. This fact translates into wider regions of applicability of the relaxation mechanism when compared to the Standard Model Higgs case. Our results show that if the electroweak scale is not fundamental but radiatively generated it is possible to generate the observed matter-antimatter asymmetry via the relaxation mechanism.

We propose a flavor symmetric approach to unify the origin of dark matter (DM) with the nonzero ${\theta }_{13}$ in the lepton sector. In this framework, the breaking of a $U(1)$ flavor symmetry to a remnant $Z_2$ ensures the stability of the DM and gives rise to a modification to the existing $A_4$-based tribimaximal neutrino mixing to attain the required nonzero values of $\sin {\theta }_{13}$. This results in a range of Higgs portal coupling of the DM which can be potentially accessible at various ongoing and future direct and collider search experiments.

The rare kaon decays $K\to \pi \nu \overline{\nu }$ are strongly suppressed in the standard model and widely regarded as processes in which new phenomena, not predicted by the standard model, may be observed. Recognizing such new phenomena requires a precise standard model prediction for the branching ratio of $K\to \pi \nu \overline{\nu }$ with controlled uncertainty for both short-distance and long-distance contributions. In this work we demonstrate the feasibility of lattice QCD calculation of the long-distance contribution to rare kaon decays with the emphasis on $K^{+}\to {\pi }^{+}\nu \overline{\nu }$. Our methodology covers the calculation of both $W\text{−}W$ and $Z$-exchange diagrams. We discuss the estimation of the power-law, finite-volume corrections and two methods to consistently combine the long-distance contribution determined by the lattice methods outlined here with the short-distance parts that can be reliably determined using perturbation theory. It is a subsequent work of our first methodology paper on $K\to \pi {\ell }^{+}{\ell }^{-}$, where the focus was made on the $\gamma$-exchange diagrams.

The full version of the QCD light-cone sum rule method is applied to tetraquarks containing a single heavy $b$ or $c$ quark. To this end, investigations of the strong vertices $X_b{X}_b\rho$ and $X_c{X}_c\rho$ are performed, where $X_b=[su][\overline{b}\overline{d}]$ and $X_c=[su][\overline{c}\overline{d}]$ are the exotic states built of four quarks of different flavors. The strong coupling constants $G_{X_b{X}_b\rho }$ and $G_{X_c{X}_c\rho }$ corresponding to these vertices are found using the $\rho$-meson leading- and higher-twist distribution amplitudes. In the calculations, $X_b$ and $X_c$ are treated as scalar bound states of a diquark and antidiquark.