We study a “heavy” QCD axion whose coupling to the standard model is dominated by $aG\tilde{G}$ but with $m_a\gg m_{\pi }{f}_{\pi }/f_a$. This is well motivated as it can solve the strong $CP$ problem while evading the axion quality problem. It also poses interesting challenges for its experimental search due to its suppressed couplings to photons and leptons. Such axion with mass around a GeV is kinematically inaccessible or poorly constrained by most experimental probes except $B$-factories. We study $B\to Ka$ transitions as a powerful probe of the heavy QCD axion by performing necessary 2-loop calculations for the first time, together with some improvement on the existing analysis strategy. We find some of the existing limits are enhanced by at least an order of magnitude. We also demonstrate that the bounds are robust against unknown UV physics. For forthcoming data sets of the Belle II experiment, we provide a projection that $f_a$ of a few TeV is within its future reach, which is relevant to the quality problem.

We study the constraints imposed by perturbative unitarity on the new physics interpretation of the muon $g-2$ anomaly. Within a Standard Model effective field theory approach, we find that scattering amplitudes sourced by effective operators saturate perturbative unitarity at about 1 PeV. This corresponds to the highest energy scale that needs to be probed in order to resolve the new physics origin of the muon $g-2$ anomaly. On the other hand, simplified models (e.g., scalar-fermion Yukawa theories) in which renormalizable couplings are pushed to the boundary of perturbativity still imply new on-shell states below 200 TeV. We finally suggest that the highest new physics scale responsible for the anomalous effect can be reached in nonrenormalizable models at the PeV scale.

Modular symmetry offers the possibility to provide an origin of discrete flavor symmetry and to break it along particular symmetry preserving directions without introducing flavons or driving fields. It is also possible to use a weighton field to account for charged fermion mass hierarchies rather than a Froggatt-Nielsen mechanism. Such an approach can be applied to flavored grand unified theories (GUTs) which can be greatly simplified using modular forms. As an example, we consider a modular version of a previously proposed $S_4\times SU(5)$ GUT, with Gatto-Sartori-Tonin and Georgi-Jarlskog relations, in which all flavons and driving fields are removed, with their effect replaced by modular forms with moduli assumed to be at various fixed points, rendering the theory much simpler. In the neutrino sector there are two right-handed neutrinos constituting a Littlest Seesaw model satisfying constrained sequential dominance where the two columns of the Dirac neutrino mass matrix are proportional to $(0,1,-1)$ and $(1,n,2-n)$ respectively, and $n=1+\sqrt{6}\approx 3.45$ is prescribed by the modular symmetry, with predictions subject to charged lepton mixing corrections. We perform a numerical analysis, showing quark and lepton mass and mixing correlations around the best fit points.

Solar neutrino experiments are highly sensitive to sources of $\nu \to \overline{\nu }$ conversions in the ${}^8\mathrm{B}$ neutrino flux. In this work, we adapt these searches to nonminimal sterile neutrino models recently proposed to explain the LSND, MiniBooNE, and reactor anomalies. The production of such sterile neutrinos in the Sun, followed by the decay chain ${\nu }_4\to \nu \phi \to \nu \nu \overline{\nu }$ with a new scalar $\phi$, results in upper limits for the neutrino mixing $|U_{e4}{|}^2$ at the per-mille level. We conclude that a simultaneous explanation of all anomalies is in tension with KamLAND, Super-Kamiokande, and Borexino constraints on the flux of solar antineutrinos. We then present other minimal models that violate parity or lepton number, and discuss the applicability of our constraints in each case. Future improvements can be expected from existing Borexino data, as well as from future searches at Super-Kamiokande with added gadolinium.

We study the bottomonium screening masses in a $2+1$ flavor QCD on the lattice using the highly improved staggered quark (HISQ) action. We focus on a wide temperature range in the region $350\mathrm{MeV}\le T<1000\mathrm{MeV}$, and perform our calculations on three different lattice spacings corresponding to temporal lattice extent of $N_{\tau }=8$, 10 and 12, in order to control the lattice cutoff effects. From a detailed study of the temperature dependence of screening masses we conclude that the ${\eta }_b(1S)$ and $\mathrm{\Upsilon }(1S)$ states melt at $T>500\mathrm{MeV}$, while the scalar and axial-vector states ${\chi }_{b0}(1P)$ and $h_b(1P)$ melt already at $T>350\mathrm{MeV}$.

We investigate the $I=1$ $\pi \pi$ interaction using the HAL QCD method in lattice QCD. We employ the ($2+1$)-flavor gauge configurations on ${32}^3\times 64$ lattice at the lattice spacing $a\approx 0.0907\mathrm{fm}$ and $m_{\pi }\approx 411\mathrm{MeV}$, in which the $\rho$ meson appears as a resonance state. We find that all-to-all propagators necessary in this calculation can be obtained with reasonable precision by a combination of three techniques, the one-end trick, the sequential propagator, and the covariant approximation averaging (CAA). The nonlocal $I=1$ $\pi \pi$ potential is determined at the next-to-next-to-leading order (${\mathrm{N}}^2\mathrm{LO}$) of the derivative expansion for the first time, and the resonance parameters of the $\rho$ meson are extracted. The obtained $\rho$ meson mass is found to be consistent with the value in the literature, while the value of the coupling $g_{\rho \pi \pi }$ turns out to be somewhat larger. The latter observation is most likely attributed to the lack of low-energy information in our lattice setup with the center-of-mass frame. Such a limitation may appear in other P-wave resonant systems and we discuss possible improvement in future. With this caution in mind, we positively conclude that we can reasonably extract the ${\mathrm{N}}^2\mathrm{LO}$ potential and resonance parameters even in the system requiring the all-to-all propagators in the HAL QCD method, which opens up new possibilities for the study of resonances in lattice QCD.

We briefly review the key aspect of the QCD instanton vacuum in relation to the quantum breaking of conformal symmetry and the trace anomaly. We use Ji’s invariant mass decomposition of the energy momentum tensor together with the trace anomaly to discuss the mass budget of the nucleon and pion in the QCD instanton vacuum. A measure of the gluon condensate in the nucleon is a measure of the compressibility of the QCD instanton vacuum as a dilute topological liquid.

Form factors of the weak ${\mathrm{\Xi }}_c\to \mathrm{\Xi }(\mathrm{\Lambda })$ transitions are calculated within the light cone QCD sum rules. The pollution coming from the contribution of the negative parity ${\mathrm{\Xi }}_c^{*}$ baryon is eliminated by considering the combinations of sum rules corresponding to the different Lorentz structures. Having obtained the form factors, the branching ratios of the ${\mathrm{\Xi }}_c\to \mathrm{\Xi }(\mathrm{\Lambda })\ell \nu$ decays are also calculated, and our predictions are compared with the results of other approaches as well as the measurements done by the BELLE and ALICE collaborations.

We study domain wall fermions and their condensation in the D3/probe D7 system. A spatially dependent mass term for the $\mathcal{N}=2$ hypermultiplet can be arranged to isolate distinct two-component fermions on two $2+1$ dimensional domain walls. We argue that the system shows condensation/mass generation analogous to the D3/probe D5 $\overline{\mathrm{D}5}$ system. The chiral condensate and pion mass can be directly computed on the domain wall. We provide evidence that these systems with the domains separated by a width $w$ have a bare (current) quark mass that scales as $1/w$ when the spatially dependent mass is large. Adding a magnetic field does not induce chiral symmetry breaking between the separated domain wall fermions, but a similar phenomenological dilaton factor can be made strong enough to introduce spontaneous symmetry breaking. We show a Gell-Man-Oakes-Renner relation for the pions in that case and also for the case where the D7 probe is in a backreacted dilaton flow geometry. The vacuum configurations can also be interpreted as having a spontaneously generated mass by a Nambu-Jona-Lasinio four fermion operator, depending on the choice of boundary conditions on fluctuations, according to Witten’s multitrace prescription.

We present a detailed study of the dynamics associated with the ghost sector of quenched QCD in the Landau gauge, where the relevant dynamical equations are supplemented with key inputs originating from large-volume lattice simulations. In particular, we solve the coupled system of Schwinger-Dyson equations that governs the evolution of the ghost dressing function and the ghost-gluon vertex, using as input for the gluon propagator lattice data that have been cured from volume and discretization artifacts. In addition, we explore the soft gluon limit of the same system, employing recent lattice data for the three-gluon vertex that enters in one of the diagrams defining the Schwinger-Dyson equation of the ghost-gluon vertex. The results obtained from the numerical treatment of these equations are in excellent agreement with lattice data for the ghost dressing function, once the latter have undergone the appropriate scale-setting and artifact elimination refinements. Moreover, the coincidence observed between the ghost-gluon vertex in general kinematics and in the soft gluon limit reveals an outstanding consistency of physical concepts and computational schemes.

We revisit the properties of positron cloud in quark nugget (QN) model of dark matter (DM). In this model, dark matter particles are represented by compact composite objects composed of a large number of quarks or antiquarks with total baryon number $B\sim {10}^{24}$. These particles have a very small number density in our galaxy which makes them “dark” to all DM detection experiments and cosmological observations. In this scenario, antiquark nuggets play special role because they may manifest themselves in annihilation with visible matter. We study electron-positron annihilation in collisions of free electrons, hydrogen and helium gases with the positron cloud of antiquark nuggets. We show that a strong electric field of antiquark nuggets destroys positronium, hydrogen and helium atoms and prevents electrons from penetrating deeply in positron cloud, thus reducing the probability of the electron-positron annihilation by nearly five orders of magnitude. Therefore, electron annihilation in the positron cloud of QNs cannot explain the observed by SPI/INTEGRAL detector photons with energy 511 keV in the center of our galaxy. These photons may be explained by a different mechanism in which QN captures protons which annihilate with antiquarks in the quark core or transform to neutrons thus reducing the QN core charge and increasing QN temperature. As a result QN loses positrons to space which annihilate with electrons there. Even more positrons are produced from charged pions resulting from the proton annihilation. Another manifestation may be emission of photons from ${\pi }^0$ decays.

Axion miniclusters are dense bound structures of dark matter axions that are predicted to form in the postinflationary Peccei-Quinn symmetry breaking scenario. Although dense, miniclusters can easily be perturbed or even become unbound by interactions with baryonic objects such as stars. Here, we characterize the spatial distribution and properties of miniclusters in the Milky Way (MW) today after undergoing these stellar interactions throughout their lifetime. We do this by performing a suite of Monte Carlo simulations which track the miniclusters’ structure and, in particular, accounts for partial disruption and mass loss through successive interactions. We consider two density profiles—Navarro-Frenk-White (NFW) and power-law (PL)—for the individual miniclusters in order to bracket the uncertainties on the minicluster population today due to their uncertain formation history. For our fiducial analysis at the solar position, we find a survival probability of 99% for miniclusters with PL profiles and 46% for those with NFW profiles. Our work extends previous estimates of this local survival probability to the entire MW. We find that towards the Galactic Center, the survival probabilities drop drastically. Although we present results for a particular initial halo mass function, our simulations can be easily recast to different models using the provided data and code (github.com/bradkav/axion-miniclusters). Finally, we comment on the impact of our results on lensing, direct, and indirect detection.

We discuss the phase diagram and properties of global vortices in the non-Hermitian parity-time-symmetric relativistic model possessing two interacting scalar complex fields. The phase diagram contains stable $\mathcal{PT}$-symmetric regions and unstable $\mathcal{PT}$-broken regions, which intertwine nontrivially with the U(1)-symmetric and U(1)-broken phases, thus forming rich patterns in the space of parameters of the model. The notion of the $\mathcal{PT}$ symmetry breaking is generalized to the interacting theory. At finite quartic couplings, the non-Hermitian model possesses classical vortex solutions in the $\mathcal{PT}$-symmetric regions characterized by broken U(1) symmetry. In the long-range limit of two-component Bose-Einstein condensates, the vortices from different condensates experience mutual dissipative dynamics unless their cores overlap precisely. For comparison, we also consider a close Hermitian analog of the system and demonstrate that the non-Hermitian two-component model possesses much richer dynamics than its Hermitian counterpart.

We explore the physical consequences of a scenario when the standard Hermitian Nambu–Jona-Lasinio (NJL) model spontaneously develops a non-Hermitian $\mathcal{PT}$-symmetric ground state via dynamical generation of an anti-Hermitian Yukawa coupling. We demonstrate the emergence of a noncompact non-Hermitian (NH) symmetry group which characterizes the NH ground state. We show that the NH group is spontaneously broken both in weak- and strong-coupling regimes. In the chiral limit at strong coupling, the NH ground state develops inhomogeneity, which breaks the translational symmetry. At weak coupling, the NH ground state is a spatially uniform state, which lies at the boundary between the $\mathcal{PT}$-symmetric and $\mathcal{PT}$-broken phases. Outside the chiral limit, the minimal NJL model does not possess a stable non-Hermitian ground state.

We calculate contributions to the anomalous magnetic moment of the muon from heavy neutral and charged Higgs bosons and new leptons in two-Higgs-doublet models extended by vectorlike leptons. We present detailed predictions of two models with type-II couplings to standard model fermions, motivated by a $Z_2$ symmetry and supersymmetry. In addition, we compare the results with the standard model extended by vectorlike leptons. We find that the model motivated by a $Z_2$ symmetry can generate much larger contributions to the magnetic moment compared to the standard model, even by two orders of magnitude due to ${\tan }^2\beta$ enhancement, while satisfying current constraints. As a consequence, the standard model explanation of the anomaly requires much larger corrections to muon couplings making this model easier to probe at future precision machines. Additionally, we find that the model with couplings motivated by supersymmetry typically leads to much smaller contributions to the magnetic moment as a result of cancellations. We also identify interesting scenarios where contributions from the charged Higgs boson can fully explain the anomaly.

The lightest neutralino, assumed to be the lightest supersymmetric particle, is proposed to be a dark matter (DM) candidate for the mass $\mathcal{O}(100)\mathrm{GeV}$. Constraints from various direct dark matter detection experiments and Planck measurements exclude a substantial region of parameter space of minimal supersymmetric standard model. However, a “mild-tempered” neutralino with dominant bino composition and a little admixture of Higgsino is found to be a viable candidate for DM. Within the minimal supersymmetric standard model framework, we revisit the allowed region of parameter space that is consistent with all existing constraints. Regions of parameters that are not sensitive to direct detection experiments, known as “blind spots,” are also revisited. Complimentary to the direct detection of DM particles, a mild-tempered neutralino scenario is explored at the LHC with the center of mass energy $\sqrt{\mathrm{s}}=13\mathrm{TeV}$ through the top-squark pair production, and its subsequent decays with the standard-model-like Higgs boson in the final state. Our considered channel is found to be very sensitive also to the blind spot scenario. Detectable signal sensitivities are achieved using the cut-based method for the high luminosity options 300 and $3000{\mathrm{fb}}^{-1}$, which are further improved by applying the multivariate analysis technique.

We discuss the implications of Affleck-Dine (AD) baryogenesis for different classes of baryon and lepton number violating processes: specially focusing on implications for neutron-antineutron ($n-\overline{n}$) oscillation. The class of AD baryogenesis scenarios we work with uses the AD field also as the inflaton which is nonminimally coupled to gravity. We find that adequate baryogenesis and no washout by the baryon number ($B$) or the lepton number ($L$) violating operators implies constraints on the observability of the process or in the case of neutrino mass with compatibility with neutrino oscillation observations. In particular for $n-\overline{n}$ oscillation, we study some of the familiar operators that connect the AD field to $n-\overline{n}$ oscillation and find that a split scalar spectrum model turns out to be most advantageous for obtaining an observable $n-\overline{n}$ while remaining consistent with AD baryogenesis. It is interesting that this spectrum is similar to a nonsupersymmetyric SO(10) model for observable $n-\overline{n}$ oscillation discussed before, suggesting that this AD scenario can be embedded into a grand unified SO(10) model. We also find that for a low scale (all scales in the 100 TeV range), there is a narrow range of parameters where the observable $n-\overline{n}$ oscillation is compatible with viable AD baryogenesis. A feature of this baryogenesis scenario for $n-\overline{n}$ oscillation is that it necessarily predicts processes with $\mathrm{\Delta }B=4$ or higher, all be it with highly suppressed amplitudes.

We study the discovery potential of the non-Standard Model (SM) heavy Higgs bosons in the Two-Higgs-Doublet Models (2HDMs) at a multi-TeV muon collider and explore the discrimination power among different types of 2HDMs. We find that the pair production of the non-SM Higgs bosons via the universal gauge interactions is the dominant mechanism once above the kinematic threshold. Single Higgs boson production associated with a pair of heavy fermions could be important in the parameter region with enhanced Yukawa couplings. For both signal final states, ${\mu }^{+}{\mu }^{-}$ annihilation channels dominate over the vector boson fusion (VBF) processes, except at high center of mass energies where the VBF processes receive large logarithmic enhancement with the increase of energies. Single Higgs boson $s$-channel production in ${\mu }^{+}{\mu }^{-}$-annihilation via the radiative return can also be important for the Type-L 2HDM in the very large $\tan \beta$ region, extending the kinematic reach of the heavy Higgs boson mass to the collider energy. Considering both the production and decay of non-SM Higgs bosons, signals can be identified over the Standard Model backgrounds. With the pair production channels via annihilation, 95% C.L. exclusion reaches in the Higgs mass up to the production mass threshold of $\sqrt{s}/2$ are possible when channels with different final states are combined. Including single production modes can extended the reach further. Different types of 2HDMs can be distinguishable for moderate and large values of $\tan \beta$.

We show that one of the simplest extensions of the Standard Model, the addition of a second Higgs doublet, when combined with a dark sector singlet scalar, allows us to $i)$ explain the long-standing anomalies in the Liquid Scintillator Neutrino Detector (LSND) and MiniBooNE (MB) while maintaining compatibility with the null result from KARMEN, $ii)$ obtain, in the process, a portal to the dark sector, and $iii)$ comfortably account for the observed value of the muon $g-2$. Three singlet neutrinos allow for an understanding of observed neutrino mass-squared differences via a Type I seesaw, with two of the lighter states participating in the interaction in both LSND and MB. We obtain very good fits to energy and angular distributions in both experiments. We explain features of the solution presented here and discuss the constraints that our model must satisfy. We also mention prospects for future tests of its particle content.