The near-threshold behavior of the $p\overline{p}$ invariant mass spectrum from the $\psi (3686)\to \gamma p\overline{p}$ decay reported recently by the BESIII Collaboration is analyzed. The enhancement in the $p\overline{p}$ invariant mass spectrum near threshold is nicely reproduced by the $p\overline{p}$ final-state interaction based on the isospin-averaged ${}^{1}S_0$ partial-wave amplitude as predicted by the Jülich nucleon-antinucleon model. Contributions from the $f_2(1910)$ or $f_2(1950)$ mesons, as promoted in earlier works, are not needed.

We consider a variational approach to the finite-temperature Yang-Mills theory in the Coulomb gauge. The partition function is computed in the ensemble of glueballs and quasigluons which emerge as eigenstates of the Coulomb gauge Hamiltonian. We compute the energy density and pressure and compare with results of lattice computations for both SU(2) and SU(3). The emergence of a phase transition is discussed.

The hadronization structure of ${\tau }^{-}\to \eta {\pi }^{-}{\pi }^0{\nu }_{\tau }$ decays is analyzed using chiral perturbation theory with resonances, considering only the contribution of the lightest meson resonances at leading order in the $1/N_C$ expansion. After imposing the asymptotic behavior of vector spectral functions ruled by QCD, unknown effective couplings are determined by fitting the ${\tau }^{-}\to \eta {\pi }^{-}{\pi }^0{\nu }_{\tau }$ branching ratio and decay spectrum to recent data. Predictions for the partner decay ${\tau }^{-}\to {\eta }^{\prime }{\pi }^{-}{\pi }^0{\nu }_{\tau }$ and the low-energy behavior of the cross section $\sigma (e^{+}{e}^{-}\to \eta {\pi }^{+}{\pi }^{-})$ are also discussed.

We consider a simple extension of the Standard Model by adding two Higgs triplets and a complex scalar singlet to its particle content. In this framework, the $CP$ symmetry is spontaneously broken at high energies by the complex vacuum expectation value of the scalar singlet. Such a breaking leads to leptonic $CP$ violation at low energies. The model also exhibits an $A_4\times Z_4$ flavor symmetry which, after being spontaneously broken at a high-energy scale, yields a tribimaximal pattern in the lepton sector. We consider small perturbations around the tribimaximal vacuum alignment condition in order to generate nonzero values of ${\theta }_{13}$, as required by the latest neutrino oscillation data. It is shown that the value of ${\theta }_{13}$ recently measured by the Daya Bay Reactor Neutrino Experiment can be accommodated in our framework together with large Dirac-type $CP$ violation. We also address the viability of leptogenesis in our model through the out-of-equilibrium decays of the Higgs triplets. In particular, the $CP$ asymmetries in the triplet decays into two leptons are computed and it is shown that the effective leptogenesis and low-energy $CP$-violating phases are directly linked.

Motivated by the upcoming Higgs analyses, we investigate the importance of the complementarity of the Higgs boson chase on the low-mass weakly interacting massive particle (WIMP) search in direct detection experiments and the gamma-ray emission from the Galactic Center measured by the Fermi-LAT telescope in the context of the $SU(3{)}_c\otimes SU(3{)}_L\otimes U(1{)}_N$. We obtain the relic abundance, thermal cross section, and the WIMP-nucleon cross section in the low-mass regime and network them with the branching ratios (BRs) of the Higgs boson in the model. We conclude that the Higgs boson search has a profound connection to the dark matter problem in our model, in particular for the case that ($M_{\mathrm{WIMP}}<60\mathrm{GeV}$) the $\mathrm{BR}(H\to 2\mathrm{WIMPs})\gtrsim 90\%$. This scenario could explain the gamma-ray emission from the Galactic Center observed by the Fermi-LAT telescope through the $b\overline{b}$ channel with a WIMP in the mass range of 25–45 GeV, while still being consistent with the current limits from XENON100 and CDMSII. However, after the recent LHC measurements concerning the Higgs, this window has been completely forfended, implying that $M_{\mathrm{WIMP}}>M_H/2$ and, consequently, ruling out any attempt to explain the Fermi-LAT observations, although still offering a region of the parameter space consistent with the current bounds. Lastly, we show that our model has a Standard Model-like Higgs boson for the regime that $M_{\mathrm{WIMP}}>M_H/2$, by computing the BRs into $bb$, $\gamma \gamma$ and $\tau \tau$.

We present an updated and extended global analysis of the constrained MSSM (CMSSM) taking into account new limits on supersymmetry from $\sim 5/\mathrm{fb}$ data sets at the LHC. In particular, in the case of the razor limit obtained by the CMS Collaboration we simulate detector efficiency for the experimental analysis and derive an approximate but accurate likelihood function. We discuss the impact on the global fit of a possible Higgs boson with mass near 125 GeV, as implied by recent data, and of a new improved limit on $\mathrm{BR}({\mathrm{B}}_{\mathrm{s}}\to {\mu }^{+}{\mu }^{-})$. We identify high posterior probability regions of the CMSSM parameters as the stau-coannihilation and the $A$-funnel region, with the importance of the latter now being much larger due to the combined effect of the above three LHC results and of dark matter relic density. We also find that the focus point region is now disfavored. Ensuing implications for superpartner masses favor even larger values than before, and even lower ranges for dark matter spin-independent cross section, ${\sigma }_p^{\mathrm{SI}}\lesssim {10}^{-9}\mathrm{pb}$. We also find that relatively minor variations in applying experimental constraints can induce a large shift in the location of the best-fit point. This puts into question the robustness of applying the usual ${\chi }^2$ approach to the CMSSM. We discuss the goodness-of-fit and find that, while it is difficult to calculate a $p$-value, the $(g-2{)}_{\mu }$ constraint makes, nevertheless, the overall fit of the CMSSM poor. We consider a scan without this constraint, and we allow $\mu$ to be either positive or negative. We find that the global fit improves enormously for both signs of $\mu$, with a slight preference for $\mu <0$ caused by a better fit to $\mathrm{BR}(\mathrm{b}\to s\gamma )$ and $\mathrm{BR}({\mathrm{B}}_{\mathrm{s}}\to {\mu }^{+}{\mu }^{-})$.

If low-energy supersymmetry is realized in nature, a seemingly contrived hierarchy in the squark mass spectrum appears to be required. We show that composite supersymmetric theories at the bottom of the conformal window can automatically yield the spectrum that is suggested by experimental data and naturalness. With a nontuned choice of parameters, the only superpartners below 1 TeV will be the partners of the Higgs, the electroweak gauge bosons, the left-handed top and bottom, and the right-handed top, which are precisely the particles needed to make weak scale supersymmetry breaking natural. In the model considered here, these correspond to composite (or partially composite) degrees of freedom via the Seiberg duality, while the other minimal supersymmetric standard model fields, with their heavier superpartners, are elementary. The key observation is that at or near the edge of the conformal window, soft supersymmetry breaking scalar and gaugino masses are transmitted only to fundamental particles at leading order. With the potential that arises from the duality, a Higgs with a 125 GeV mass, with nearly standard model production rates, is naturally accommodated without tuning. The lightest ordinary superpartner is either the lightest stop or the lightest neutralino. If it is the stop, it is natural for it to be almost degenerate with the top, in which case it decays to top by emitting a very soft gravitino, making it quite difficult to find this mode at the LHC and more challenging to find supersymmetry in general, yielding a simple realization of the stealth supersymmetry idea. We analyze four benchmark spectra in detail.

The recent discovery at the LHC by the CMS and ATLAS collaborations of the Higgs boson presents, at long last, direct probes of the mechanism for electroweak symmetry breaking. While it is clear from the observations that the new particle plays some role in this process, it is not yet apparent whether the couplings and widths of the observed particle match those predicted by the Standard Model. In this paper, we perform a global fit of the Higgs results from the LHC and Tevatron. While these results could be subject to as-yet-unknown systematics, we find that the data are significantly better fit by a Higgs with a suppressed width to gluon-gluon and an enhanced width to $\gamma \gamma$, relative to the predictions of the Standard Model. After considering a variety of new physics scenarios which could potentially modify these widths, we find that the most promising possibility is the addition of a new colored, charged particle, with a large coupling to the Higgs. Of particular interest is a light, and highly mixed, stop, which we show can provide the required alterations to the combination of $gg$ and $\gamma \gamma$ widths.

We calculate critical couplings and string tensions in $SU(2)$ and $SU(3)$ pure lattice gauge theory by a simple and inexpensive technique of two-lattice matching of renormalization group block transformations. The transformations are potential moving decimations generating plaquette actions with large number of group characters and exhibit rapid approach to a unique renormalized trajectory. Fixing the critical coupling ${\beta }_c(N_{\tau })$ at one value of temporal lattice length $N_{\tau }$ by Monte Carlo (MC) simulation, the critical couplings for any other value of $N_{\tau }$ are then obtained by lattice matching of the block decimations. We obtain ${\beta }_c(N_{\tau })$ values over the range $N_{\tau }=3–32$ and find agreement with MC simulation results to within a few percent in all cases. A similar procedure allows the calculation of string tensions with similarly good agreement with MC data.

It is sometimes speculated that the sign problem that afflicts many quantum field theories might be reduced or even eliminated by choosing an alternative domain of integration within a complexified extension of the path integral (in the spirit of the stationary phase integration method). In this paper we start to explore this possibility somewhat systematically. A first inspection reveals the presence of many difficulties but—quite surprisingly—most of them have an interesting solution. In particular, it is possible to regularize the lattice theory on a Lefschetz thimble, where the imaginary part of the action is constant and disappears from all observables. This regularization can be justified in terms of symmetries and perturbation theory. Moreover, it is possible to design a Monte Carlo algorithm that samples the configurations in the thimble. This is done by simulating, effectively, a five-dimensional system. We describe the algorithm in detail and analyze its expected cost and stability. Unfortunately, the measure term also produces a phase which is not constant and it is currently very expensive to compute. This residual sign problem is expected to be much milder, as the dominant part of the integral is not affected, but we have still no convincing evidence of this. However, the main goal of this paper is to introduce a new approach to the sign problem, that seems to offer much room for improvements. An appealing feature of this approach is its generality. It is illustrated first in the simple case of a scalar field theory with chemical potential, and then extended to the more challenging case of QCD at finite baryonic density.

We present a solution to the sign problem in dynamical random matrix simulations of a two-matrix model at nonzero chemical potential. The sign problem, caused by the complex fermion determinants, is solved by gathering the matrices into subsets, whose sums of determinants are real and positive even though their cardinality only grows linearly with the matrix size. A detailed proof of this positivity theorem is given for an arbitrary number of fermion flavors. We performed importance sampling Monte Carlo simulations to compute the chiral condensate and the quark number density for varying chemical potential and volume. The statistical errors on the results only show a mild dependence on the matrix size and chemical potential, which confirms the absence of sign problem in the subset method. This strongly contrasts with the exponential growth of the statistical error in standard reweighting methods, which was also analyzed quantitatively using the subset method. Finally, we show how the method elegantly resolves the Silver Blaze puzzle in the microscopic limit of the matrix model, where it is equivalent to QCD.

Two measures are defined to evaluate the coupling strength of smeared interpolating operators to hadronic states at a variety of momenta. Of particular interest is the extent to which strong overlap can be obtained with individual high-momentum states. This is vital to exploring hadronic structure at high-momentum transfers on the lattice and addressing interesting phenomena observed experimentally. We consider a novel idea of altering the shape of the smeared operator to match the Lorentz contraction of the probability distribution of the high-momentum state and show a reduction in the relative error of the two-point function by employing this technique. Our most important finding is that the overlap of the states becomes very sharp in the smearing parameters at high momenta, and fine tuning is required to ensure strong overlap with these states.

We extend the confined covariant constituent quark model that was previously developed by us for mesons to the baryon sector. In our numerical calculation we use the same values for the constituent quark masses and the infrared cutoff as have been previously used in the meson sector. In a first application we describe the static properties of the proton and neutron, and the $\Lambda$ hyperon (magnetic moments and charge radii) and the behavior of the nucleon form factors at low momentum transfers. We discuss in some detail the conservation of gauge invariance of the electromagnetic transition matrix elements in the presence of a nonlocal coupling of the baryons to the three constituent quark fields.

We calculate the inclusive production of $h_c(h_b)$ at $e^{+}{e}^{-}$ colliders with the center-of-mass energy from the CLEO-c energy to $Z^0$ boson mass at leading order of nonrelativistic QCD. At $Z^0$ boson mass, the cross sections are $39\sim 703\mathrm{fb}$ for $h_c(1P)$, $37\sim 61\mathrm{fb}$ for $h_b(1P)$, and $44\sim 73\mathrm{fb}$ for $h_b(2P)$. At the $B$-factories, it is $86\sim 212\mathrm{fb}$ for $h_c(1P)$. For $h_c$ at the CLEO-c and $h_b(1P,2P)$ at the $B$-factories, the perturbative QCD expansion is not good and the results are much smaller than the experimental measurements. It is clearly shown in all the results that the color-octet state $({}^{1}S_0^8)$ contributes dominantly while the color-singlet state $({}^{1}P_1^1)$ contributes a small or even negative part, in contrast to the case of inclusive $J/\psi$ production where the color-singlet state is found to contribute dominantly.

We consider the structure of divergences in Drell-Yan process with small transverse momentum. The factorization proof is not trivial because various kinds of divergences are intertwined in the collinear and soft parts at high orders. We prescribe a method to disentangle the divergences in the framework of the soft-collinear effective theory. The rapidity divergence is handled by introducing the $\delta$ regulator in the collinear Wilson lines. The collinear part, which consists of the transverse-momentum-dependent parton distribution function, is free of the rapidity divergence after the soft zero-bin subtraction. There still remains the problem of mixing between the ultraviolet and infrared divergences, which forbids the renormalization group description. We show that the mixing is cancelled by the soft function. This suggests that the collinear and soft parts should be treated as a whole in constructing a consistent factorization theorem. The renormalization group behavior of the combined collinear and soft parts is presented explicitly at one loop. We also show that the integrated parton distribution function can be obtained by integrating the transverse-momentum-dependent parton distribution function over the transverse momentum.

TeV scale new physics, e.g., large extra dimensions or models with anomalous triple vector boson couplings, can lead to excesses in various kinematic regions on the semileptonic productions of $pp\to WW\to l\nu jj$ at the CERN LHC, which, although suffer from large QCD background compared with the pure leptonic channel $pp\to WW\to l\nu l\nu$, can benefit from larger production rates and the reconstructable four-body mass $M_{l\nu jj}$. We study the search sensitivity through the $l\nu jj$ channel at the 7 TeV LHC on relevant new physics via probing the hard tails on the reconstructed $M_{l\nu jj}$ and the transverse momentum of leptonically decayed $W$ boson ($P_{TW}$), taking into account main backgrounds and including the parton shower and detector simulation effects. Our results show that with integrated luminosity of $5{\mathrm{fb}}^{-1}$, the LHC can already discover or exclude a large parameter region of the new physics, e.g., a 95% C.L. can be set on the large extra dimensions with a cutoff scale up to 1.5 TeV, and the $WWZ$ anomalous coupling down to, e.g., $|{\lambda }_Z|\sim 0.1$. Results are also given for the 8 TeV LHC.

We present a method, which constructs a suitable deformation vector in loop momentum space, when the loop integration is done numerically with the help of the subtraction method. The method presented here extends previously discussed techniques from the massless case to the general case of arbitrary masses in the loop.

We make a systematic investigation on the two-body nonleptonic decays $B_c\to D_{(s)}^{(*)}P$, $D_{(s)}^{(*)}V$, by employing the perturbative QCD approach based on $k_T$ factorization, where $P$ and $V$ denote any light pseudoscalar meson and vector meson, respectively. We predict the branching ratios and direct $CP$ asymmetries of these $B_c$ decays and also the transverse polarization fractions of $B_c\to D_{(s)}^{*}V$ decays. It is found that the nonfactorizable emission diagrams and annihilation-type diagrams have remarkable effects on the physical observables in many channels, especially the color-suppressed and annihilation-dominant decay modes. A possible large direct $CP$ violation is predicted in some channels; and a large transverse polarization contribution which can reach $50\%\sim 70\%$ is predicted in some of the $B_c\to D_{(s)}^{*}V$ decays.

Fixed-order QCD radiative corrections to the vector-boson and Higgs associated production channels, $pp\to VH$ ($V=W^{\pm }$, $Z$), at hadron colliders are well understood. We combine higher-order perturbative QCD calculations with soft gluon resummation of both threshold logarithms and logarithms which are important at a low transverse momentum of the $VH$ pair. We study the effects of both types of logarithms on the scale dependence of the total cross section and on various kinematic distributions. The next-to-next-to-next-to-leading logarithmic resummed total cross sections at the LHC are almost identical to the fixed-order perturbative next-to-next-to-leading order rates, indicating the excellent convergence of the perturbative QCD series. Resummation of the $VH$ transverse momentum ($p_T$) spectrum provides reliable results for small values of $p_T$ and suggests that implementing a jet veto will significantly decrease the cross sections.

The existence of heavy neutrinos mediating neutrino masses via a type-I seesaw can be directly probed at the LHC, or indirectly in rare lepton flavor-violating processes. The synergy between these two approaches requires a direct measurement of the heavy neutrino couplings. We discuss a strategy to perform such measurements at the LHC in the context of left-right symmetric models, which is also applicable to other models implementing a type-I or type-III seesaw. We demonstrate that the ambiguities in the determination of the heavy neutrino mixing parameters can be resolved by performing an exclusive analysis of dilepton final states, discriminated by flavor and missing energy.