Generically, the gravitational-wave or tensor-mode contribution to the primordial curvature spectrum of inflation is tiny if the field range of the inflaton is much smaller than the Planck scale. We show that this pessimistic conclusion is naturally avoided in a rather broad class of small-field models. More specifically, we consider models where an axionlike shift symmetry keeps the inflaton potential flat (up to nonperturbative cosine-shaped modulations), but inflation nevertheless ends in a waterfall regime, as is typical for hybrid inflation. In such hybrid natural inflation scenarios (examples are provided by Wilson line inflation and fluxbrane inflation), the slow-roll parameter $ϵ$ can be sizable during an early period (relevant for the cosmic microwave background spectrum). Subsequently, $ϵ$ quickly becomes very small before the tachyonic instability eventually terminates the slow-roll regime. In this scenario, one naturally generates a considerable tensor-mode contribution in the curvature spectrum, collecting nevertheless the required amount of $e$-foldings during the final period of inflation. While nonobservation of tensors by Planck is certainly not a problem, a discovery in the medium- to long-term future is realistic.

We consider nonlocal gravity theories that include tensor nonlocalities. We show that in the cosmological context, the tensor nonlocalities, unlike scalar ones, generically give rise to growing modes. An explicit example with quadratic curvature terms is studied in detail. Possible consequences for recent nonlocal cosmological models proposed in the literature are also discussed.

The objective of this paper is to study static spherically symmetric noncommutative wormhole solutions in the framework of $f(T)$ gravity. We construct $f(T)$ field equations in covariant and effective energy-momentum tensor forms to make a correspondence with general relativity. It is observed that the violation of energy conditions to support the nonstandard wormhole is due to the effective energy-momentum tensor. We explore the noncommutative wormhole solutions for two cases: (i) assume a viable power-law $f(T)$ model to construct the shape function and (ii) a particular shape function is taken to construct the $f(T)$ model. In the first case, only exotic matter forms a wormhole structure in teleparallel gravity, whereas for $f(T)$ gravity, normal matter threads these structures except for a particular range of $r$. For the constructed $f(T)$ model, there does not exist a physically acceptable wormhole solution similar to the teleparallel case.

We revisit cosmic microwave background constraints on the abundance of millicharged particles based on the Planck data. The stringent limit ${\Omega }_{\mathrm{mcp}}{h}^2<0.001$ (95% CL) may be set using the cosmic microwave background data alone if millicharged particles participate in the acoustic oscillations of baryon-photon plasma at the recombination epoch. The latter condition is valid for a wide region of charges and masses of the particles. Adding the millicharged component to $\Lambda \mathrm{CDM}$ shifts the preferred scalar spectral index of primordial perturbations to somewhat larger values as compared to the minimal model, even approaching the Harrison-Zeldovich spectrum under some assumptions.

Unparticle contributions to the recently measured decay mode $B_s\to {\mu }^{+}{\mu }^{-}$ are analyzed. We consider only the scalar unparticles because vector unparticles are expected to provide negligible contributions. Assuming that the relevant coupling constants are real, we present allowed regions of coupling constants and the scaling dimension of the scalar unparticle. While the measured value of the branching ratio is very close to the standard model predictions, one cannot exclude the possible contributions from unparticles.

Gluons at small $x$ in high-energy nuclei overlap in the longitudinal direction, so the nucleus acts as a single source of gluons, like higher Fock components in a single nucleon, which contribute to inelastic collisions with a high multiplicity of produced hadrons. This similarity helps to make a link between nuclear effects in $pA$ and high-multiplicity $pp$ collisions. Such a relation is well confirmed by data for the $J/\Psi$ production rate in high-multiplicity $pp$ events measured recently in the ALICE experiment. Broadening of $J/\Psi$ transverse momentum is predicted for high-multiplicity $pp$ collisions.

Many methods have been developed for measuring the mass of invisible particles that only use kinematic information available at hadron colliders. Because a particle is identified by its mass, these methods are critical when distinguishing between dark matter and fake dark matter, where a neutrino or other massless states can mimic a dark-matter signal. However, the uncertainty associated with measuring the mass of an invisible particle could be so large that it is indistinguishable from a neutrino. Monte Carlo is used to estimate lower bounds on how heavy an invisible particle must be in order for it to be distinguishable from a massless one at 95% CL, which we estimate to be $\mathcal{O}(10\mathrm{GeV})$. This result, to a good approximation, is independent of the way the massive final-state particle is produced. If there is a light dark-matter particle with mass $\mathcal{O}(10\mathrm{GeV})$, its presence will be difficult to unambiguously identify at the LHC, using kinematic information alone.

Inspired by the dark matter searches in the low mass region, we study the type II two Higgs doublet model with a light gauge singlet weakly interacting massive particle stabilized by a $Z_2$ symmetry. The real singlet is required to only couple to the non–standard model Higgs. We investigate singlet candidates with different spins as well as isospin violating effect. The parameter space favored by LHC data in the two Higgs doublet model and hadronic uncertainties in WIMP-nucleon elastic scattering are also taken into account. We find only the scalar singlet in the isospin conserving case leads to a major overlap with the region of interest of most direct detection experiments.

The discovery at the LHC of a scalar particle with properties that are so far consistent with the standard model Higgs boson is one of the most important advances in the history of particle physics. The challenge of future collider experiments is to determine whether its couplings will show deviations from the standard model Higgs, as this would indicate new physics at the TeV scale, and also to probe the flavor structure of the Yukawa couplings. As a benchmark alternative to the standard model Higgs, we consider a generic two Higgs doublet model and analyze the precision to which the LHC14, an International Linear Collider (ILC) operating at 250, 500, 1000 GeV, and a 125 GeV muon collider can determine the gauge and Yukawa couplings. We allow for correlations among the couplings. We include the impact of a Higgs total width measurement, indirectly at the LHC and ILC and by a direct scan at the muon collider. We also discuss pattern relations among the couplings that can test for singlet or doublet Higgs extensions of two Higgs doublet models.

Dark matter may consist of light, very weakly interacting bosons, produced nonthermally in the early Universe. Prominent examples of such very weakly interacting slim particles are axions and hidden photons. Direct detection experiments for such particles are based on the conversion of these particles into photons. This can be done in resonant cavities, featuring a resonant enhancement, or by using suitably shaped reflecting surfaces that allow for broadband searches. In this paper we want to elucidate the relation between the two setups and study the transition from resonant to broadband searches. This then allows us to determine the sensitivity of off-resonance cavity searches for cavities much larger than the wavelength of the generated photons.

The best limit on the strong flavor changing neutral current (FCNC) anomalous couplings was obtained using the direct top production process at the Large Hadron Collider by the ATLAS Collaboration. We perform a similar analysis but using a next-to-leading order generator, MEtop. We then show how the limits could be improved if the FCNC single top process $pp\to tj$ would be included as signal. Finally we discuss a slightly modified analysis with an extra hard jet in the final state.

In this manuscript, we present a complete study of the Sudakov double logarithms resummation for various hard processes in $eA$ and $pA$ collisions in the small-$x$ saturation formalism. We first employ a couple of slightly different formalisms to perform the one-loop analysis of the Higgs boson production process in $pA$ collisions, and demonstrate that Sudakov-type logarithms arise as the leading correction and that they can be systematically resummed in addition to the usual small-$x$ resummation. We further study the Sudakov double logarithms for other processes such as heavy quark pair production and back-to-back dijet production in $eA$ and $pA$ collisions through detailed calculation of the corresponding one-loop diagrams. As the most important contribution from the one-loop correction, the Sudakov factor should play an important role in the phenomenological study of saturation physics in the $pA$ programs at RHIC and the LHC.

In this work, we explore the production of the newly observed charged charmoniumlike state $Z_c(3900{)}^{\pm }$ by the photoproduction process $\gamma p\to Z_c(3900{)}^{+}n$. Our numerical result indicates that the maximum of the calculated total cross section of $\gamma p\to Z_c(3900{)}^{+}n$ can reach up to the order of $0.1\mu b$. Furthermore, the Dalitz plot analysis is performed by considering the Pomeron exchange as the background contribution. This analysis shows that the $Z_c(3900{)}^{+}$ signal can be distinguished from the background easily and the best energy window of searching for $Z_c(3900{)}^{+}$ is $\sqrt{s}\simeq 7\mathrm{GeV}$, which is important information for further experimental study of $Z_c(3900{)}^{+}$ by meson photoproduction.

In the framework of the heavy baryon perturbation theory, in which the two-pion exchange is considered, the physical properties of heavy baryon and anti-heavy baryon systems are revisited. The potentials between heavy baryon and anti-heavy baryon are extracted in a holonomic form. Based on the extracted potentials, the $S$-wave scattering phase shifts and scattering lengths of ${\Lambda }_c–{\overline{\Lambda }}_c$ and ${\Sigma }_c–{\overline{\Sigma }}_c$ are calculated. From these scattering features, it is found that the ${\Lambda }_c–{\overline{\Lambda }}_c$ system can be bound only when the value of the coupling constant at the baryon-Goldstone-boson vertex is larger than that calculated from the decay data of the ${\Sigma }_c({\Sigma }_c^{*})\to {\Lambda }_c\pi$ process. The binding condition for the ${\Sigma }_c–{\overline{\Sigma }}_c$ system is also examined. The binding possibilities of these systems deduced from the scattering calculations are also checked by the bound state calculation and the binding energies are obtained if the system can be really bound. The binding possibility of the ${\Lambda }_b–{\overline{\Lambda }}_b$ system is investigated as well.

We report a measurement of the branching fraction of the decay $B_s^0\to J/\psi \varphi (1020)$, evidence and a branching fraction measurement for $B_s^0\to J/\psi f_2^{\prime }(1525)$, and the determination of the total $B_s^0\to J/\psi K^{+}{K}^{-}$ branching fraction, including the resonant and nonresonant contributions to the $K^{+}{K}^{-}$ channel. We also determine the $S$-wave contribution within the $\varphi (1020)$ mass region. The absolute branching fractions are $\mathcal{B}[B_s^0\to J/\psi \varphi (1020)]=(1.25\pm 0.07(\mathrm{stat})\pm 0.08(\mathrm{syst})\pm 0.22(f_s))\times {10}^{-3}$, $\mathcal{B}[B_s^0\to J/\psi f_2^{\prime }(1525)]=(0.26\pm 0.06(\mathrm{stat})\pm 0.02(\mathrm{syst})\pm 0.05(f_s))\times {10}^{-3}$, and $\mathcal{B}[B_s^0\to J/\psi K^{+}{K}^{-}]=(1.01\pm 0.09(\mathrm{stat})\pm 0.10(\mathrm{syst})\pm 0.18(f_s))\times {10}^{-3}$, where the last systematic error is due to the branching fraction of $b\overline{b}\to B_s^{(*)}{B}_s^{(*)}$. The branching fraction ratio is found to be $\mathcal{B}[B_s^0\to J/\psi f_2^{\prime }(1525)]/\mathcal{B}[B_s^0\to J/\psi \varphi (1020)]=(21.5\pm 4.9(\mathrm{stat})\pm 2.6(\mathrm{syst}))\%$. All results are based on a $121.4{\mathrm{fb}}^{-1}$ data sample collected at the ${\rm Y}(5S)$ resonance by the Belle experiment at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider.

It is widely believed that fully hadronic final states are not competitive in searches for new physics at the Large Hadron Collider due to the overwhelming QCD backgrounds. In this paper, we present a particle-level study of the topology arising when a TeV-scale resonance decays to two Higgs bosons and these subsequently decay to $b\overline{b}$, leading to two back-to-back boosted dijet systems. We show that selecting events with this topology dramatically reduces all backgrounds, thus enabling very competitive searches for new physics in a variety of models. For a resonance with mass 1 TeV and width around 60 GeV, we find that ATLAS or CMS could have a sensitivity to a $\sigma \times \mathrm{BR}$ as small as a few fb with the LHC data collected in 2012. These conclusions are also relevant to the boosted $Zh\to b\overline{b}b\overline{b}$ and $ZZ\to b\overline{b}b\overline{b}$ final states, which would further increase the potential sensitivity to new physics as well as to standard model processes like longitudinal vector boson scattering.

In this article, we tentatively identify the charmed mesons $D_J(2580)$, $D_J^{*}(2650)$, $D_J(2740)$, $D_J^{*}(2760)$, $D_J(3000)$, and $D_J^{*}(3000)$ observed by the LHCb Collaboration according to their spin, parity, and masses. Then we study their strong decays to the ground state charmed mesons plus light pseudoscalar mesons with the heavy meson effective theory in the leading order approximation, and we obtain explicit expressions of the decay widths. The ratios among the decay widths can be used to confirm or reject the assignments of the newly observed charmed mesons. The strong coupling constants in the decay widths can be fitted to the experimental data in the future at the LHCb, BESIII, KEK-B, and $\overline{\mathrm{P}}\mathrm{ANDA}$.

We perform a detailed study of top-quark partner production in the $t\overline{t}$ plus large missing energy final state at the LHC, presenting results for both scalar and fermionic top-quark partners in the semileptonic and dileptonic decay modes of the top quarks. We compare the results of several simulation tools: leading order matrix elements, next-to-leading order (NLO) matrix elements, leading order plus parton shower simulations, and merged samples that contain the signal process with an additional hard jet radiated. We find that predictions from leading order plus parton shower simulations can significantly deviate from NLO QCD or LO merged samples and do not correctly model the kinematics of the $t\overline{t}+E_{T,\mathrm{miss}}$ signature. They are therefore not a good framework for modeling this new physics signature. On the other hand, the acceptances obtained with a merged sample of the leading-order process together with the radiation of an additional hard jet are in agreement with the NLO predictions. We also demonstrate that the scale variation of the inclusive cross section, plus that of the acceptance, does not accurately reflect the uncertainty of the cross section after cuts, which is typically larger. We show the importance of including higher-order QCD corrections when using kinematic distributions to determine the spin of the top-quark partner.

The intensity of scalar $a_0(980)$, $f_0(980)$ and tensor $a_2(1320)$, $f_2(1270)$ mesons production at VEPP-2000 (BINP, Novosibirsk) and the upgraded $\mathrm{DA}\Phi \mathrm{NE}$ (Frascati, Italy) in the processes $e^{+}{e}^{-}\to a_0(f_0,a_2,f_2)\gamma$ is calculated. For the scalar meson production the calculation is performed with the help of the vector dominance model (VDM) and the kaon loop model. Only the VDM approach is used in the tensor meson case. Note that the processes $e^{+}{e}^{-}\to a_2(f_2)\gamma$ have not been studied in the energy region of VEPP-2000. It turned out that in the VEPP-2000 energy region $1.7–2.0\mathrm{GeV}$ ${\sigma }_{e^{+}{e}^{-}\to a_2(f_2)\gamma }\sim 10\mathrm{pb}$, and ${\sigma }_{e^{+}{e}^{-}\to a_0(f_0)\gamma }\sim 0.1\mathrm{pb}$. Photon angle distribution and the spin density matrices of $a_2$ and $f_2$ production are also calculated.

We present measurements of asymmetries in angular distributions of leptons produced in $t\overline{t}$ events in proton-antiproton collisions at the Fermilab Tevatron Collider. We consider final states where the $W^{\pm }$ bosons from top quark and antiquark decays both decay into $\ell \nu$ ($\ell =e$, $\mu$) resulting in oppositely charged dilepton final states with accompanying jets. Using $9.7{\mathrm{fb}}^{-1}$ of integrated luminosity collected with the D0 detector, we find the asymmetries in lepton pseudorapidity compatible with predictions based on the standard model.