We study the oscillations of neutron and strange stars in $R^2$ gravity. More precisely, the nonradial $f$ modes are examined and the differences with pure general relativity are investigated. Using these results, we build several gravitational wave asteroseismology relations. Our goal is to determine up to what extent these relations are equation of state independent and whether they deviate enough from general relativity in order to produce an observable effect. The results show that the differences coming from $R^2$ gravity are up to 10%, which will be difficult to observe in the near future. On the other hand, the small deviations in some of the asteroseismology relations show that they are not only equation of state independent, but they are also quite insensitive to the gravitational theory. That is why solving the inverse problem can give us quite robust estimates of the neutron star parameters.

We use overlap fermions as valence quarks to calculate meson masses in a wide quark mass range on the $2+1$-flavor domain-wall fermion gauge configurations generated by the RBC and UKQCD Collaborations. The well-defined quark masses in the overlap fermion formalism and the clear valence quark mass dependence of meson masses observed from the calculation facilitate a direct derivation of physical current quark masses through a global fit to the lattice data, which incorporates $O(a^2)$ and $O(m_c^4{a}^4)$ corrections, chiral extrapolation, and quark mass interpolation. Using the physical masses of $D_s$, $D_s^{*}$ and $J/\psi$ as inputs, Sommer’s scale parameter $r_0$ and the masses of charm quark and strange quark in the $\overline{\mathrm{MS}}$ scheme are determined to be $r_0=0.465(4)(9)\mathrm{fm}$, $m_c^{\overline{\mathrm{MS}}}(2\mathrm{GeV})=1.118(6)(24)\mathrm{GeV}$ (or $m_c^{\overline{\mathrm{MS}}}(m_c)=1.304(5)(20)\mathrm{GeV}$), and $m_s^{\overline{\mathrm{MS}}}(2\mathrm{GeV})=0.101(3)(6)\mathrm{GeV}$, respectively. Furthermore, we observe that the mass difference of the vector meson and the pseudoscalar meson with the same valence quark content is proportional to the reciprocal of the square root of the valence quark masses. The hyperfine splitting of charmonium, $M_{J/\psi }-M_{{\eta }_c}$, is determined to be 119(2)(7) MeV, which is in good agreement with the experimental value. We also predict the decay constant of $D_s$ to be $f_{D_s}=254(2)(4)\mathrm{MeV}$. The masses of charmonium $P$-wave states ${\chi }_{c0}$, ${\chi }_{c1}$ and $h_c$ are also in good agreement with experiments.

We present unquenched lattice QCD results for the matrix elements of four-fermion operators relevant to the description of the neutral $K$ and $D$ mixing in the standard model and its extensions. We have employed simulations with $N_f=2+1+1$ dynamical sea quarks at three values of the lattice spacings in the interval 0.06–0.09 fm and pseudoscalar meson masses in the range 210–450 MeV. Our results are extrapolated to the continuum limit and to the physical pion mass. Renormalization constants have been determined nonperturbatively in the RI-MOM scheme. In particular, for the kaon bag parameter, which is relevant for the ${\overline{K}}^0-K^0$ mixing in the standard model, we obtain $B_K^{\mathrm{RGI}}=0.717(24)$.

We present an exploratory numerical study on the lattice of the color structure of the wave functionals of the SU(3) Yang–Mills theory in the presence of a $q\overline{q}$ static pair. In a spatial box with periodic boundary conditions, we discuss the fact that all states contributing to the Feynman propagation kernel are global color singlets. We confirm this numerically by computing the correlations of gauge-fixed Polyakov lines with color-twisted boundary conditions in the time direction. The values of the lowest energies in the color singlet and octet external source sectors agree within statistical errors, confirming that both channels contribute to the lowest (global singlet) state of the Feynman kernel. We then study the case of homogeneous boundary conditions in the time direction for which the gauge fixing is not needed. In this case, the lowest energies extracted in the singlet external source sector agree with those determined with periodic boundary conditions, while in the octet sector, the correlator is compatible with being null within our statistical errors. Therefore, consistently only the singlet external source contribution has a nonvanishing overlap with the null-field wave functional.

We study the renormalization of $SU(N_c)$ gauge theories on general anisotropic lattices, to one-loop order in perturbation theory, employing the background field method. The results are then applied in the context of two different approaches to hadronic high-energy scattering. In the context of the Euclidean nonperturbative approach to soft high-energy scattering based on Wilson loops, we refine the nonperturbative justification of the analytic continuation relations of the relevant Wilson-loop correlators, required to obtain physical results. In the context of longitudinally rescaled actions, we study the consequences of one-loop corrections on the relation between the $SU(N_c)$ gauge theory and its effective description in terms of two-dimensional principal chiral models.

We propose to study the pentaquark candidates of $P_c^{+}(4380)$ and $P_c^{+}(4450)$ in $J/\psi$ photoproduction and look for further experimental evidence for their nature. Since the photoproduction process does not satisfy the so-called “anomalous triangle singularity” condition their presence in $J/\psi$ photoproduction would conclude that they should be genuine states and provide further evidence for their existence.

The associated production of a Higgs boson and a top-quark pair, $t\overline{t}H$, in proton-proton collisions is addressed in this paper for a center of mass energy of 13 TeV at the LHC. Dileptonic final states of $t\overline{t}H$ events with two oppositely charged leptons and four jets from the decays $t\to b{W}^{+}\to b{\ell }^{+}{\nu }_{\ell }$, $\overline{t}\to \overline{b}{W}^{-}\to \overline{b}{\ell }^{-}{\overline{\nu }}_{\ell }$ and $h\to b\overline{b}$, are used. Signal events, generated with MadGraph5_aMC@NLO, are fully reconstructed by applying a kinematic fit. New angular distributions of the decay products as well as angular asymmetries are explored in order to improve discrimination of $t\overline{t}H$ signal events over the dominant irreducible background contribution, $t\overline{t}b\overline{b}$. Even after the full kinematic fit reconstruction of the events, the proposed angular distributions and asymmetries are still quite different in the $t\overline{t}H$ signal and the dominant background ($t\overline{t}b\overline{b}$).

We present the differential rates for exclusive $\overline{B}\to X{\ell }_1{\ell }_2$, where ${\ell }_1$ is a charged massless lepton and ${\ell }_2$ is a charged or neutral massless lepton and $X$ is a mesonic system up to spin 2. The cases of interest are semileptonic $\overline{B}\to X_{\{c,u\}}{\ell }^{-}{\overline{\nu }}_{\ell }$ decays, and $\overline{B}\to X_s{\ell }^{-}{\ell }^{+}$ where the dilepton can be $c\overline{c}$ resonances or nonresonant electroweak penguins. We consider helicity amplitudes having nonzero relative phases that can be potential new sources for $CP$ violation. Our motivations for these additional phases include a complex right-handed admixture in the hadronic weak charged current for the semileptonic decays and complex Wilson coefficients in the effective Hamiltonians for the electroweak penguin decays. We demonstrate the efficacy of a novel technique of projecting out the individual angular moments in the full rate expression in a model-independent fashion. Our work is geared toward ongoing data analyses by BABAR and LHCb.

The magnetic moments of $J^P={\frac{3}{2}}^{+}$ decuplet baryons have been calculated in the chiral constituent quark model ($\chi \mathrm{CQM}$) with explicit results for the contribution coming from the valence quark polarizations, sea quark polarizations, and their orbital angular momentum. Since the $J^P={\frac{3}{2}}^{+}$ decuplet baryons have short lifetimes, the experimental information about them is limited. The $\chi \mathrm{CQM}$ has important implications for chiral symmetry breaking as well as SU(3) symmetry breaking since it works in the region between the QCD confinement scale and the chiral symmetry breaking scale. The predictions in the model not only give a satisfactory fit when compared with the experimental data but also show improvement over the other models. The effect of the confinement on quark masses has also been discussed in detail and the results of $\chi$CQM are found to improve further with the inclusion of effective quark masses.

We report a direct lattice QCD calculation of the strange nucleon electromagnetic form factors $G_E^s$ and $G_M^s$ in the kinematic range $0\le Q^2\lesssim 1.2{\mathrm{GeV}}^2$. For the first time, both $G_E^s$ and $G_M^s$ are shown to be nonzero with high significance. This work uses closer to physical lattice parameters than previous calculations, and achieves an unprecedented statistical precision by implementing a recently proposed variance reduction technique called hierarchical probing. We perform model-independent fits of the form factor shapes using the $z$-expansion and determine the strange electric and magnetic radii and magnetic moment. We compare our results to parity-violating electron-proton scattering data and to other theoretical studies.

We consider the two-point function of the gauge field in Lorentz-breaking theories with higher-derivative extension of the Dirac Lagrangian. We show that the Carroll-Field-Jackiw term naturally arises in this theory as a quantum correction being perfectly finite and thus displaying no ambiguities. Also, the finiteness of this term at the low energy limit and the absence of large Lorentz violating corrections allows to avoid the fine-tuning problem.

We determine the asymptotic dynamics of the U(N) doubly periodic BPS monopole in Yang-Mills-Higgs theory, called a monopole wall, by exploring its Higgs curve using the Newton polytope and amoeba. In particular, we show that the monopole wall splits into subwalls when any of its moduli become large. The long-distance gauge and Higgs field interactions of these subwalls are Abelian, allowing us to derive an asymptotic metric for the monopole wall moduli space.

We study the merger of binary neutron stars using different realistic, microphysical nuclear equations of state, as well as incorporating magnetic field and neutrino cooling effects. In particular, we concentrate on the influence of the equation of state on the gravitational wave signature and also on its role, in combination with cooling and electromagnetic effects, in determining the properties of the hypermassive neutron star resulting from the merger, the production of neutrinos, and the characteristics of ejecta from the system. The ejecta we find are consistent with other recent studies that find soft equations of state produce more ejecta than stiffer equations of state. Moreover, the degree of neutron richness increases for softer equations of state. In light of reported kilonova observations (associated to GRB 130603B and GRB 060614) and the discovery of relatively low abundances of heavy, radioactive elements in deep sea deposits (with respect to possible production via supernovae), we speculate that a soft equation of state (EOS) might be preferred—because of its significant production of sufficiently neutron rich ejecta—if such events are driven by binary neutron star mergers. We also find that realistic magnetic field strengths, obtained with a subgrid model tuned to capture magnetic amplification via the Kelvin-Helmholtz instability at merger, are generally too weak to affect the gravitational wave signature postmerger within a time scale of $\approx 10\mathrm{ms}$ but can have subtle effects on the postmerger dynamics.

By explicitly constructing the Hilbert space, Higuchi showed that there is a lower bound on the mass of a minimally-coupled free spin-2 field on a curved background A. Higuchi, Nucl. Phys. B282, 397 (1987). Using the vacuum persistence amplitude, we show that this bound is modified by taking into account additional terms not prohibited by symmetry in the case of a maximally symmetric spacetime. This result can further be generalized to the maximally symmetric space case, such as the Friedmann-Robertson-Walker universe, and its corresponding bound of the deformation parameter is discussed.

We study the effects exerted by the backreaction of long-wavelength fluctuations on stochastic inflation. In the cases of power-law and Starobinsky inflation, these effects are too weak to terminate the stochastic growth of the inflaton field. However, in the case of the cyclic ekpyrotic scenario, the backreaction effects prevent the unlimited growth of the scalar field.

We explore constraints on the scalar coupling in a family nonuniversal $U(1{)}^{\prime }$ extension of the standard model free from anomalies with a complex scalar dark matter particle. From unitarity and stability of the Higgs potential, we find the full set of bounds and order relations for the scalar coupling constants. Using recent data from the CERN-LHC collider, we study the signal strength of the diphoton Higgs decay, which imposes very stringent bounds to the scalar couplings and other scalar parameters, including parameters associated to the dark matter. Taking into account these constraints, the observable relic density of the Universe, and the limits from LUX collaboration for direct detection, we obtain allowed masses for the dark matter particle as low as 55 GeV. By assuming that the lightest scalar boson of the model corresponds to the observed Higgs boson, we evaluate deviations from the standard model of the trilineal Higgs self-coupling. The conditions from unitarity, stability and Higgs diphoton decay data allow trilineal deviations in the range $0\le \delta g\lesssim -72\%$.

With the ongoing experimental interest in exploring the excited hadron spectrum, evaluations of the matrix elements describing the formation and decay of such states via radiative processes provide us with an important connection between theory and experiment. In particular, determinations obtained via the lattice allow for a direct comparison of QCD expectation with experimental observation. Here we present the first light-quark determination of the $\rho \to \pi \gamma$ transition form factor from lattice QCD using dynamical quarks. Using the PACS-CS $2+1$ flavor QCD ensembles we are able to obtain results across a range of masses, to the near physical value of $m_{\pi }=156\mathrm{MeV}$. An important aspect of our approach is the use of variational methods to isolate the desired QCD eigenstate. For low-lying states, such techniques facilitate the removal of excited state contributions. In principle, the method enables one to consider arbitrary eigenstates. We find our results are in accord with the nonrelativistic quark model for heavy masses. In moving towards the light-quark regime we observe an interesting quark mass dependence, contrary to the quark model expectation. Comparison of our light-quark result with experimental determinations highlights a significant discrepancy suggesting that disconnected sea-quark loop contributions may play a significant role in fully describing this process.

We examine the pairs of neutrino mixing matrix and suggest pairs that can be used in the construction of new mixing patterns, with “pair” denoting the equality of the modulus of a pair of matrix elements. The results show that the trimaximal mixing in ${\nu }_2$ and the $\mu \text{−}\tau$ interchange symmetry are good choices under current experimental results. The two cases of bipair mixing pattern depend on the mass hierarchy of neutrinos. We also derive constraints on the $CP$ phase by the pairs. The results are compatible with the maximal $CP$ violation in most cases that are both self-consistent and consistent with experimental results.