We revisit the recent limits from LHCb on a Majorana neutrino $N$ in the mass range 250–5000 MeV [R. Aaij et al. (LHCb Collaboration), Phys. Rev. Lett. 112, 131802 (2014).]. These limits are among the best currently available, and they will be improved soon by the addition of data from Run 2 of the LHC. LHCb presented a model-independent constraint on the rate of like-sign leptonic decays, and then derived a constraint on the mixing angle $V_{\mu 4}$ based on a theoretical model for the $B$ decay width to $N$ and the $N$ lifetime. The model used is unfortunately unsound. We revise the conclusions of the paper based on a decay model similar to the one used for the $\tau$ lepton and provide formulas useful for future analyses.

We investigate the effect of the inverse magnetic catalysis (IMC) on charged $\rho$ meson condensation at finite temperature in the framework of the Nambu–Jona-Lasinio model, where mesons are calculated to the leading order of $1/N_c$ expansion. The IMC for chiral condensate has been considered using three different approaches: incorporating the chiral condensate from lattice data, using the running coupling constant, and introducing the chiral chemical potential, respectively. It is observed that with no IMC effect included, the critical magnetic field $e{B}_c$ for charged $\rho$ condensation increases monotonically with the temperature. However, including IMC substantially affects the polarized charged $\rho$ condensation around the critical temperature $T_c$ of the chiral phase transition: first, the critical magnetic field $e{B}_c$ for the charged $\rho$ condensation decreases with the temperature, reaches its minimum value around $T_c$, and then increases with the temperature. It is quite surprising that the charged $\rho$ can condense above the critical temperature of chiral phase transition with a even smaller critical magnetic field comparing its vacuum value. The Nambu–Jona-Lasinio model calculation shows that in the temperature region of $1–1.5T_c$, the critical magnetic field for charged $\rho$ condensation is rather small and in the region of $e{B}_c\sim 0.15–0.3{\mathrm{GeV}}^2$, which suggests that high temperature superconductor might be created through noncentral heavy ion collisions at LHC energies.

We report new constraints on the size of large extra dimensions from data collected by the MINOS experiment between 2005 and 2012. Our analysis employs a model in which sterile neutrinos arise as Kaluza-Klein states in large extra dimensions and thus modify the neutrino oscillation probabilities due to mixing between active and sterile neutrino states. Using Fermilab’s Neutrinos at the Main Injector beam exposure of $10.56\times 10^{20}$ protons on target, we combine muon neutrino charged current and neutral current data sets from the Near and Far Detectors and observe no evidence for deviations from standard three-flavor neutrino oscillations. The ratios of reconstructed energy spectra in the two detectors constrain the size of large extra dimensions to be smaller than $0.45\mu \mathrm{m}$ at 90% C.L. in the limit of a vanishing lightest active neutrino mass. Stronger limits are obtained for nonvanishing masses.

We consider a scalar particle in a background formed by two counterpropagating plane waves. Two cases are studied: (i) dynamics at a magnetic node and (ii) zero initial transverse canonical momentum. The Lorentz and Klein-Gordon equations are solved for these cases and approximations analyzed. For the magnetic-node solution (homogeneous, time-dependent electric field), the modified Volkov wave function which arises from a high-energy approximation is found to be inaccurate for all energies and the solution itself unstable when the photon emission (nonlinear Compton scattering) is included. For the zero initial transverse canonical momentum case, in both quantum and classical cases, forbidden parameter regimes, absent in the plane-wave model, are identified.

We present a detailed study of the Vaidya solution and its generalization in de Rham-Gabadadze-Tolley (dRGT) theory. Since the diffeomorphism invariance can be restored with the Stückelberg fields ${\varphi }^a$ introduced, there is a new invariant $I^{ab}=g^{\mu \nu }{\partial }_{\mu }{\varphi }^a{\partial }_{\nu }{\varphi }^b$ in the massive gravity, which adds to the ones usually encountered in general relativity. There is no conventional Vaidya solution if we choose unitary gauge. In this paper, we obtain three types of self-consistent ansatz with some nonunitary gauge, and find accordingly the Vaidya, generalized Vaidya, and furry Vaidya solution. As by-products, we obtain a series of furry black hole. The Vaidya solution and its generalization in dRGT massive gravity describe the black holes with a variable horizon.

Regardless of the long history of gauge theories, it is not well recognized under which condition gauge fixing at the action level is legitimate. We address this issue from the Lagrangian point of view, and prove the following theorem on the relation between gauge fixing and Euler-Lagrange equations: In any gauge theory, if a gauge fixing is complete, i.e., the gauge functions are determined uniquely by the gauge conditions, the Euler-Lagrange equations derived from the gauge-fixed action are equivalent to those derived from the original action supplemented with the gauge conditions. Otherwise, it is not appropriate to impose the gauge conditions before deriving Euler-Lagrange equations as it may in general lead to inconsistent results. The criterion to check whether a gauge fixing is complete or not is further investigated. We also provide applications of the theorem to scalar-tensor theories and make comments on recent relevant papers on theories of modified gravity, in which there are confusions on gauge fixing and counting physical degrees of freedom.

We study the Kaluza-Klein dimensional reduction of the Lovelock-Cartan theory in five-dimensional spacetime, with a compact dimension of $S^1$ topology. We find cosmological solutions of the Friedmann-Robertson-Walker class in the reduced spacetime. The torsion and the fields arising from the dimensional reduction induce a nonvanishing energy-momentum tensor in four dimensions. We find solutions describing expanding, contracting, and bouncing universes. The model shows a dynamical compactification of the extra dimension in some regions of the parameter space.

We present a purely geometric renormalization scheme for metric spaces (including uncolored graphs), which consists of a coarse graining and a rescaling operation on such spaces. The coarse graining is based on the concept of quasi-isometry, which yields a sequence of discrete coarse grained spaces each having a continuum limit under the rescaling operation. We provide criteria under which such sequences do converge within a superspace of metric spaces, or may constitute the basin of attraction of a common continuum limit, which hopefully may represent our space-time continuum. We discuss some of the properties of these coarse grained spaces as well as their continuum limits, such as scale invariance and metric similarity, and show that different layers of space-time can carry different distance functions while being homeomorphic. Important tools in this analysis are the Gromov-Hausdorff distance functional for general metric spaces and the growth degree of graphs or networks. The whole construction is in the spirit of the Wilsonian renormalization group (RG). Furthermore, we introduce a physically relevant notion of dimension on the spaces of interest in our analysis, which, e.g., for regular lattices reduces to the ordinary lattice dimension. We show that this dimension is stable under the proposed coarse graining procedure as long as the latter is sufficiently local, i.e., quasi-isometric, and discuss the conditions under which this dimension is an integer. We comment on the possibility that the limit space may turn out to be fractal in case the dimension is noninteger. At the end of the paper we briefly mention the possibility that our network carries a translocal far order that leads to the concept of wormhole spaces and a scale dependent dimension if the coarse graining procedure is no longer local.

Sudden singularities occur in Friedmann-Robertson-Walker (FRW) spacetimes when the scale factor remains finite and different from zero while some of its derivatives diverge. After proper rescaling, the scale factor close to such a singularity at $t=0$ takes the form $a(t)=1+c|t{|}^{\eta }$ (where $c$ and $\eta$ are parameters and $\eta \ge 0$). We investigate analytically and numerically the geodesics of free and gravitationally bound particles through such sudden singularities. We find that even though free particle geodesics go through sudden singularities for all $\eta \ge 0$, bound systems get dissociated (destroyed) for a wide range of the parameter $c$. For $\eta <1$ bound particles receive a diverging impulse at the singularity and get dissociated for all positive values of the parameter $c$. For $\eta >1$ [sudden future singularities (SFS)] bound systems get a finite impulse that depends on the value of $c$ and get dissociated for values of $c$ larger than a critical value $c_{\mathrm{cr}}(\eta ,{\omega }_0)>0$ that increases with the value of $\eta$ and the rescaled angular velocity ${\omega }_0$ of the bound system. We obtain an approximate equation for the analytical estimate of $c_{\mathrm{cr}}(\eta ,{\omega }_0)$. We also obtain its accurate form by numerical derivation of the bound system orbits through the singularities. Bound system orbits through big brake singularities ($c<0$, $1<\eta <2$) are also derived numerically and are found to get disrupted (deformed) at the singularity. However, they remain bound for all values of the parameter $c$ considered.

It is well known that some black holes can act as accelerators for particles without spin. Recently, some works have considered the collision of two spinning particles in the background of Schwarzschild and Kerr black holes and it has been shown that the center-of-mass energy of the test particles is related to the spin. In this paper we extend the results to some more general cases. We consider Kerr-Newman black holes as accelerators for spinning particles. We derive the center-of-mass energy of the spinning particles and use numerical method to investigate how the center-of-mass energy is affected by the properties of the black holes and spinning particles.

ESPRESSO is a high-resolution-ultrastable spectrograph for the Very Large Telescope, whose commissioning will start in 2017. One of its key science goals is to test the stability of nature’s fundamental couplings with unprecedented accuracy and control of possible systematics. A total of 27 nights of the ESPRESSO Consortium’s guaranteed time observations (GTO) will be spent in testing the stability of the fine-structure constant and other fundamental couplings. A set of 14 priority optimal targets have been selected for the GTO period. Here we briefly discuss the criteria underlying this selection and describe the selected targets, and then we present detailed forecasts of the impact of these measurements on fundamental physics and cosmology, focusing on dark energy constraints and using future supernova Type Ia surveys as a comparison point. We show how canonical reconstructions of the dark energy equation of state are improved by the extended redshift range enabled by these spectroscopic measurements, and also quantify additional improvements foreseen for a future ELT-HIRES instrument.

Advanced gravitational-wave observatories, such as LIGO and Virgo, will detect hundreds of gravitational-wave signals emitted by binary black holes in the next few years. The collection of detected sources is expected to have certain properties. It is expected that a selection bias will exist toward higher-mass systems, that most events will be oriented with their angular momentum pointing to or away from Earth, and that quiet events will be much more numerous than loud events. In this paper, we show how all these assumptions are only true for existing detectors and do not have any universality. Using a network of proposed third-generation gravitational-wave detectors, we show how each of these assumptions must be revised, and we discuss several consequences on the characterization of the sources.

We propose a loop-induced neutrino mass model, in which we introduce several exotic fermions and bosons with an $SU(2{)}_L$ multiplet, and discuss various phenomenologies such as lepton flavor violations, the muon anomalous magnetic moment, nonstandard interacting neutrinoless double beta decay, the relic density of dark matter, and the possibility of the spin-independent direct detection searches, imposing the constraints of oblique parameters. And we show a benchmark point to satisfy all the constraints and discuss our predictions.

We study the scaling with the number of colors, $N_c$, of the weak amplitudes mediating kaon mixing and decay. We evaluate the amplitudes of the two relevant current-current operators on the lattice for $N_c=3–7$. We conclude that the subleading $1/N_c$ corrections in ${\widehat{B}}_K$ are small, but those in the $K\to \pi \pi$ amplitudes are large and fully anticorrelated in the $I=0$, 2 isospin channels. We briefly comment on the implications for the $\mathrm{\Delta }I=1/2$ rule.

In this paper, we carry out a low-temperature scan of the phase diagram of dense two-color QCD with $N_f=2$ quarks. The study is conducted using lattice simulation with rooted staggered quarks. At small chemical potential, we observe the hadronic phase, where the theory is in a confining state, chiral symmetry is broken, the baryon density is zero, and there is no diquark condensate. At the critical point $\mu =m_{\pi }/2$, we observe the expected second-order transition to Bose-Einstein condensation of scalar diquarks. In this phase, the system is still in confinement in conjunction with nonzero baryon density, but the chiral symmetry is restored in the chiral limit. We have also found that in the first two phases the system is well described by chiral perturbation theory. For larger values of the chemical potential, the system turns into another phase, where the relevant degrees of freedom are fermions residing inside the Fermi sphere, and the diquark condensation takes place on the Fermi surface. In this phase, the system is still in confinement, chiral symmetry is restored, and the system is very similar to the quarkyonic state predicted by $\mathrm{SU}(N_c)$ theory at large $N_c$.

An event generator for diphoton ($\gamma \gamma$) production in hadron collisions that includes associated jet production up to two jets has been developed using a subtraction method based on the limited leading-log subtraction. The parton shower (PS) simulation to restore the subtracted divergent components involves both quantum electrodynamic (QED) and quantum chromodynamic radiation, and QED radiation at very small $Q^2$ is simulated by referring to a fragmentation function (FF). The PS/FF simulation has the ability to enforce the radiation of a given number of energetic photons. The generated events can be fed to PYTHIA to obtain particle (hadron) level event information, which enables us to perform realistic simulations of photon isolation and hadron-jet reconstruction. The simulated events, in which the loop-mediated $gg\to \gamma \gamma$ process is involved, reasonably reproduce the diphoton kinematics measured at the LHC. Using the developed simulation, we found that the two-jet processes significantly contribute to diphoton production. A large two-jet contribution can be considered as a common feature in electroweak-boson production in hadron collisions although the reason is yet to be understood. Discussion concerning the treatment of the underlying events in photon isolation is necessary for future higher precision measurements.

We compute the resummed on-shell $W^{+}{W}^{-}$ production cross section under a jet veto at the LHC to partial ${\mathrm{N}}^3\mathrm{LL}$ order matched to the fixed-order NNLO result. Differential NNLO cross sections are obtained from an implementation of $q_T$ subtraction in Sherpa. The two-loop virtual corrections to the $q\overline{q}\to W^{+}{W}^{-}$ amplitude, used in both fixed-order and resummation predictions, are extracted from the public code qqvvamp. We perform resummation using soft collinear effective theory, with approximate beam functions where only the logarithmic terms are included at two-loop. In addition to scale uncertainties from the hard matching scale and the factorization scale, rapidity scale variations are obtained within the analytic regulator approach. Our resummation results show a decrease in the jet veto cross section compared to NNLO fixed-order predictions, with reduced scale uncertainties compared to $\mathrm{NNLL}+\mathrm{NLO}$ resummed predictions. We include the loop-induced $gg$ contribution with jet veto resummation to $\mathrm{NLL}+\mathrm{LO}$. The prediction shows good agreement with recent LHC measurements.

Using the recently obtained $P_{gq}$ splitting function we extend the low-$x$ evolution equation for gluons to account for contributions originating from quark-to-gluon splitting. In order to write down a consistent equation we resum virtual corrections coming from the gluon channel and demonstrate that this implies a suitable regularization of the $P_{gq}$ singularity, corresponding to a soft emitted quark. We also note that the obtained equation is in a straightforward manner generalized to a nonlinear evolution equation which takes into account effects due to the presence of high gluon densities.

The production of $D$ mesons in proton-proton collisions at the LHCb detector is studied. We consider the single production of $D^0/{\overline{D}}^0$, $D^{\pm }$, $D^{*\pm }$, and $D_s^{\pm }$ mesons and correlation spectra in the production of $D\overline{D}$ and $DD$ pairs at the $\sqrt{S}=7\mathrm{TeV}$ and $\sqrt{S}=13\mathrm{TeV}$. In case of the single $D$-meson production we calculate differential cross sections over transverse momentum $p_T$ while in the pair $D\overline{D}$, $DD$-meson production the cross sections are calculated over the azimuthal angle difference $\mathrm{\Delta }\phi$, rapidity difference $\mathrm{\Delta }y$, invariant mass of the pair $M$ and over the $p_T$ of the one meson from a pair. The cross sections are obtained at the leading order of the parton Reggeization approach using Kimber-Martin-Ryskin unintegrated parton distribution functions in a proton. To describe the $D$-meson production we use universal scale-dependent $c$-quark and gluon fragmentation functions fitted to $e^{+}{e}^{-}$ annihilation data from CERN LEP1. Our predictions find a good agreement with the LHCb Collaboration data within uncertainties and without free parameters.

We investigate the branching ratios, the polarization fractions, the direct $CP$-violating asymmetries, and the relative phases in 20 nonleptonic decay modes of $B\to f_{1}V$ within the framework of the perturbative QCD approach at leading order with $f_1$ including two ${}^3{P}_1$-axial-vector states $f_1(1285)$ and $f_1(1420)$. Here, $B$ denotes $B^{+}$, $B^0$, and $B_s^0$ mesons and $V$ stands for the lightest vector mesons $\rho$, $K^{*}$, $\omega$, and $\varphi$, respectively. The $B_s^0\to f_{1}V$ decays are studied theoretically for the first time in the literature. Together with the angle ${\varphi }_{f_1}\approx ({24}_{-2.7}^{+3.2}{)}^{\circ }$ extracted from the measurement through $B_{d/s}\to J/\psi f_1(1285)$ modes for the $f_1(1285)-f_1(1420)$ mixing system, it is of great interest to find phenomenologically some modes such as the tree-dominated $B^{+}\to f_1{\rho }^{+}$ and the penguin-dominated $B^{+,0}\to f_1{K}^{*+,0}$, $B_s^0\to f_1\varphi$ with large branching ratios around $\mathcal{O}({10}^{-6})$ or even $\mathcal{O}({10}^{-5})$, which are expected to be measurable at the LHCb and/or the Belle-II experiments in the near future. The good agreement (sharp contrast) of branching ratios and decay pattern for $B^{+}\to f_1{\rho }^{+}$, $B^{+,0}\to f_1(1285)K^{*+,0}[B^{+,0}\to f_1(1420)K^{*+,0}]$ decays between QCD factorization and perturbative QCD factorization predictions can help us to distinguish these two rather different factorization approaches via precision measurements, which would also be helpful for us in exploring the annihilation decay mechanism through its important roles for the considered $B\to f_{1}V$ decays.