Vector-like quarks are introduced in various new physics models beyond the standard model (SM) at the TeV scale. We especially consider the case that the quark is singlet (triplet) under the $\mathrm{SU}(2{)}_L$ ($\mathrm{SU}(3{)}_c$) gauge group and couples only to the third-generation quarks of the SM. The vector-like quark of this kind is often called a top partner. The top partner $t_p$ decays into $bW$, $tZ$, and $th$. In the ATLAS and CMS Collaborations, the top partner has been searched in the final states of $bW$ and $tZ$, while the search based on the decay mode $t_p\to th$ has not been started yet. However, the decay into $th$ is important, since it is significantly enhanced if some strong dynamics exists in the TeV scale. In the presence of a light Higgs boson, the decay mode $t_p\to th$ followed by $h\to b\overline{b}$ produces three bottom quarks. We study the sensitivity for the top partner using multi-$\mathrm{b}$-jet events at the 8 TeV run of the Large Hadron Collider (LHC) experiment. The multi-$\mathrm{b}$-jet events turn out to play a complementary role to the existing $t_p\to bW$ and $tZ$ searches by the ATLAS and CMS Collaborations.

Many extensions of the leptonic sector of the minimal supersymmetric standard model (MSSM) are known, most of them leading to observable flavor violating effects. It has recently been shown that the 1-loop contributions to lepton flavor violating three-body decays $l_i\to 3l_j$ involving the $Z^0$ boson may be dominant, that is, much more important than the usual photonic penguins. Other processes like $\mu$-$e$ conversion in nuclei and flavor violating $\tau$ decays into mesons are also enhanced by the same effect. This is for instance also the case in the MSSM with trilinear $R$-parity violation. The aim of this work is to derive new bounds on the relevant combinations of $R$-parity violating couplings and to compare them with previous results in the literature. For heavy supersymmetric spectra the limits are improved by several orders of magnitude. For completeness, also constraints coming from flavor violating $Z^0$-decays and tree-level decay channels $l\to l_i{l}_j{l}_k$ are presented for a set of benchmark points.

In minimal anomaly-mediated supersymmetry-breaking models, tachyonic sleptons are avoided by introducing a common scalar mass similar to the one introduced in minimal supergravity. This may lead to nonminimal flavor-violating interactions, e.g., in the squark sector. In this paper, we analyze the viable anomaly-mediated supersymmetry-breaking parameter space in the light of the latest limits on low-energy observables and LHC searches, complete our analytical calculations of flavor-violating supersymmetric particle production at hadron colliders with those related to gluino production, and study the phenomenological consequences of nonminimal flavor violation in anomaly-mediated supersymmetry-breaking scenarios at the LHC. Related cosmological aspects are also briefly discussed.

Axions or similar hypothetical pseudoscalar bosons may have a small $CP$-violating scalar Yukawa interaction $g_s^N$ with nucleons, causing macroscopic monopole-dipole forces. Torsion-balance experiments constrain $g_p^e{g}_s^N$, whereas $g_p^N{g}_s^N$ is constrained by the depolarization rate of ultra-cold neutrons or spin-polarized nuclei. However, the pseudoscalar couplings $g_p^e$ and $g_p^N$ are strongly constrained by stellar energy-loss arguments and $g_s^N$ by searches for anomalous monopole-monopole forces, together providing the most restrictive limits on $g_p^e{g}_s^N$ and $g_p^N{g}_s^N$. The laboratory limits on $g_s^N$ are currently the most restrictive constraints on $CP$-violating axion interactions.

A direct calculation of the mixed action parameter ${\Delta }_{\mathrm{mix}}$ with valence overlap fermions on a domain-wall fermion sea is presented. The calculation is performed on four ensembles of the $2+1$ flavor domain-wall gauge configurations: ${24}^3\times 64$ ($a{m}_l=0.005$, $a=0.114\mathrm{fm}$) and ${32}^3\times 64$ ($a{m}_l=0.004$, 0.006, 0.008, $a=0.085\mathrm{fm}$). For pion masses close to 300 MeV we find ${\Delta }_{\mathrm{mix}}=0.030(6){\mathrm{GeV}}^4$ at $a=0.114\mathrm{fm}$ and ${\Delta }_{\mathrm{mix}}=0.033(12){\mathrm{GeV}}^4$ at $a=0.085\mathrm{fm}$. The results are quite independent of the lattice spacing and they are significantly smaller than the results for valence domain-wall fermions on asqtad sea or those of valence overlap fermions on clover sea. Combining the results extracted from these two ensembles, we get ${\Delta }_{\mathrm{mix}}=0.030(6)(5){\mathrm{GeV}}^4$, where the first error is statistical and the second is the systematic error associated with the fitting method.

We study heavy hadron spectroscopy near open bottom thresholds. We employ $\mathrm{B}$ and ${\mathrm{B}}^{*}$ mesons as effective degrees of freedom near the thresholds, and consider meson exchange potentials between them. All possible composite states which can be constructed from the $\mathrm{B}$ and ${\mathrm{B}}^{*}$ mesons are studied up to the total angular momentum $J\le 2$. We consider, as exotic states, isosinglet states with exotic $J^{PC}$ quantum numbers and isotriplet states. We solve numerically the Schrödinger equation with channel couplings for each state. The masses of twin resonances ${\mathrm{Z}}_{\mathrm{b}}(10610)$ and ${\mathrm{Z}}_{\mathrm{b}}(10650)$ recently found by Belle are reproduced. We predict several possible bound and/or resonant states in other channels for future experiments.

Using the recently developed formalism we carry out the first complete calculation of kinematic power corrections to the helicity amplitudes of deeply-virtual Compton scattering to the twist-four accuracy for a study case of a (pseudo)scalar target. Our main result is that both finite-$t$, $\sim t/Q^2$, and target mass, $\sim m^2/Q^2$, twist-four kinematic power corrections turn out to be factorizable, at least to the leading order in the strong coupling. The structure of these corrections is discussed and a short model study of their numerical impact is presented.

The baryon differential spectrum of the baryon decay ${\Lambda }_b\to {\Lambda }_c\ell {\overline{\nu }}_{\ell }$ will hopefully be measured in detail at LHCb. We obtain some new results on the form factors in the heavy quark expansion of Heavy Quark Effective Theory that can be useful in the interpretation of the data. We formulate a sum rule for the elastic subleading form factor $A(w)$ at order $1/m_Q$, that originates from the Lagrangian perturbation ${\mathcal{L}}_{\mathrm{kin}}$. In the sum rule appear only the intermediate states $(j^P,J^P)=(0^{+},{\frac{1}{2}}^{+})$, entering also in the $1/m_Q^2$ correction to the axial form factor $G_1(w)$, that contributes to the differential rate at zero recoil $w=1$. This result, together with another sum rule in the forward direction for $|G_1(1){|}^2$, allows to obtain a lower bound for the correction at zero recoil $-{\delta }_{1/m_Q^2}^{(G_1)}$ in terms of the derivative $A_1^{\prime }(1)$ and the slope ${\rho }_{\Lambda }^2$ and curvature ${\sigma }_{\Lambda }^2$ of the elastic Isgur-Wise function ${\xi }_{\Lambda }(w)$. Another theoretical implication is that $A^{\prime }(1)$ must vanish for some relation between ${\rho }_{\Lambda }^2$ and ${\sigma }_{\Lambda }^2$, as well as for ${\rho }_{\Lambda }^2\to 0$, establishing a nontrivial correlation between the leading IW function ${\xi }_{\Lambda }(w)$ and the subleading one $A(w)$. A phenomenological estimation of these two functions allows to obtain a lower bound on $-{\delta }_{1/m_Q^2}^{(G_1)}$.

We revisit the transverse single spin asymmetry in the angular distribution of a Drell-Yan dilepton pair. We study this asymmetry by using twist-3 collinear factorization, and we obtain the same result both in covariant gauge and in the light-cone gauge. Moreover, we have checked the electromagnetic gauge invariance of our calculation. Compared to previous calculations we properly treat the transverse momentum expansion, and as a consequence our final expression for the asymmetry differs from all the previous results given in the literature. The overall sign of this asymmetry is as important as the sign of the Sivers asymmetry in Drell-Yan.

It is widely believed that quadratic divergences severely restrict natural constructions of particle physics models beyond the standard model (SM). Supersymmetry provides a beautiful solution, but the recent LHC experiments have excluded large parameter regions of supersymmetric extensions of the SM. It will now be important to reconsider whether we have been misinterpreting the quadratic divergences in field theories. In this paper, we revisit the problem from the viewpoint of the Wilsonian renormalization group and argue that quadratic divergences—which can always be absorbed into a position of the critical surface—should be simply subtracted in model constructions. Such a picture gives another justification to the argument [W. A. Bardeen, Report No. FERMILAB-CONF-95-391-T] that the scale invariance of the SM, except for the soft-breaking terms, is an alternative solution to the naturalness problem. It also largely broadens possibilities of model constructions beyond the SM since we just need to take care of logarithmic divergences, which cause mixings of various physical scales and runnings of couplings.

We have considered the existence of a dependence of the entanglement entropy on the cosmological horizon surface area also in several accelerating models of the current universe both for a quintessence scalar field and for a phantom-energy scenario. It is shown that if a quintessence vacuum cosmic field is considered then, though the case for $w>-1$ satisfies a second law for entanglement entropy, when $w<-1$ such a law is violated. It is finally noted that the entanglement entropy and the distinct formulations of cosmic holography share common future surfaces which are optimal screen for the latter descriptions.

We study a nonrelativistic fermionic retarded Green’s function by making use of a fermion on the Lifshitz geometry with critical exponent $z=2$. With a natural boundary condition, respecting the symmetries of the model, the resultant retarded Green’s function exhibits a number of interesting features including a flat band. We also study the finite temperature and finite chemical potential cases where the geometry is replaced by Lifshitz black hole solutions.

It is possible to formulate fluid dynamics in terms of group-valued variables. This is particularly suited to the cases where the fluid has non-Abelian charges and is coupled to non-Abelian gauge fields. We explore this formulation further in this paper. An action for a fluid of relativistic particles (with and without spin) is given in terms of the Lorentz and Poincaré (or de Sitter) groups. Considering the case of particles with flavor symmetries, a general fluid action which also incorporates all flavor anomalies is given. The chiral magnetic and chiral vorticity effects as well as the consequences of the mixed gauge-gravity anomaly are discussed.

Within the superfield formalism, we study the dynamical generation of mass to the gauge superfield in the noncommutative two-dimensional supersymmetric Schwinger model. We show that the radiatively generated mass for the gauge superfield does not depend on the noncommutative parameter $\Theta$ up to one-loop order.

The group classification of models of axion electrodynamics with arbitrary self-interaction of axionic field is carried out. It is shown that extensions of the basic Poincaré invariance of these models appear only for constant and exponential interactions. The related conservation laws are discussed. The maximal continuous symmetries of the 3d Chern-Simons electrodynamics and Carroll-Field-Jackiw electrodynamics are presented. Using the Inönü-Wigner contraction the nonrelativistic limit of equations of axion electrodynamics is found. Exact solutions for the electromagnetic and axion fields are discussed including those which describe propagation with group velocities faster than the speed of light. However these solutions are causal since the corresponding energy velocities are subluminal.

In the present article the thermodynamic results of the Lee-Wick partner infested universe have been applied in a toy model where there is one Lee-Wick partner to each of the standard model particles, and moreover, the longitudinal degrees of freedom of the massive partners of the standard massless gauge bosons are neglected at high temperatures. For practical purposes, the chiral fermionic sector of Lee-Wick theories requires two Lee-Wick partners per fermion, which opens up the possibility for a negative energy density of the early universe. A toy Lee-Wick model with one fermionic partner relaxes such oddities and hence is easy to deal with. In a similar way, the longitudinal degrees of freedom of the massive gauge boson partners also have the potential to yield negative energy densities, and thus those will be neglected in a toy model study. In such a toy model one can analytically calculate the time-temperature relation in the very early radiation dominated universe which shows interesting new physics. The article also tries to point out how a Lee-Wick particle dominated early cosmology transforms into the standard cosmological model. Based on the results of this toy model analysis a brief discussion is presented on the more realistic model, which can accommodate two Lee-Wick partners for each standard fermionic field and the longitudinal degree of freedom of partners of the gauge fields. It has been shown that such a universe is mostly very difficult to attain, but there are certain conditions where one can indeed think of such a universe which can evolve into the standard cosmological universe in a short time duration.

In this work we present a new class of real scalar field models admitting strongly interactive kink solutions. Instead of the usual exponential asymptotic behavior these topological solutions exhibit a power-law one. We investigate the interaction force between a pair of kink/antikink solutions both analytically and numerically, by integrating the time dependent field equations of the model. Furthermore, working within the first-order framework, we analyze the linear stability of these solutions. The stability analysis leads to Schödinger-like equations with potentials which, despite admitting no bound states, lead to strong resonance peaks. We argue that these properties are important for some possible physical applications.

We use the recently proposed generalized on-shell representation for scattering amplitudes and a consistency test to explore the space of tree-level consistent couplings in four-dimensional Minkowski space-time. The extension of the notion of constructibility implied by the generalized on-shell representation, i.e. the possibility to reconstruct at tree level all the scattering amplitudes from the three-particle ones, together with the imposition of the consistency conditions at four-particle level, allow us to rediscover all the known theories characterized by three-particle couplings and propagator $1/P^2$, and their algebra structure if any. Interestingly, this analysis seems to leave room for high-spin couplings, provided that at least the requirement of locality is weakened. We do not claim to have found tree-level consistent high-spin theories, but rather that our methods show signatures of them and very likely, with a suitable modification, they can be a good framework to perform a systematic search.

A strategy for computing the $\overline{\psi }\psi$ anomalous dimension at the fixed point in infrared-conformal gauge theories from lattice simulations is discussed. The method is based on the scaling of the spectral density of the Dirac operator or rather its integral, the mode number. It is relatively cheap, mainly for two reasons: (a) the mode number can be determined with quite high accuracy, and (b) the $\overline{\psi }\psi$ anomalous dimension is extracted from a fit of several observables on the same set of configurations (no scaling in the Lagrangian parameters is needed). As an example the $\overline{\psi }\psi$ anomalous dimension has been computed in the SU(2) theory with 2 Dirac fermions in the adjoint representation of the gauge group and has been found to be ${\gamma }_{*}=0.371(20)$. In this particular case, the proposed strategy has proved to be very robust and effective.

We consider a theory of massless reduced quantum electrodynamics (${\mathrm{RQED}}_{d_{\gamma },d_e}$), e.g., a quantum field theory where the $U(1)$ gauge field lives in $d_{\gamma }$-space-time dimensions while the fermionic field lives in a reduced space-time of $d_e$ dimensions ($d_e⩽d_{\gamma }$). In the case where $d_{\gamma }=4$ such RQEDs are renormalizable while they are super-renormalizable for $d_{\gamma }<4$. The 2-loop electromagnetic current correlation function is computed exactly for a general ${\mathrm{RQED}}_{d_{\gamma },d_e}$. Focusing on ${\mathrm{RQED}}_{4,3}$, the corresponding $\beta$-function is shown to vanish which implies the scale invariance of the theory. Interaction correction to the 1-loop vacuum polarization, ${\Pi }_1$, of ${\mathrm{RQED}}_{4,3}$ is found to be $\Pi ={\Pi }_1(1+0.056\alpha )$ where $\alpha$ is the fine structure constant. The scaling dimension of the fermion field is computed at 1-loop and is shown to be anomalous for ${\mathrm{RQED}}_{4,3}$.