Collider signals of dark photons are an exciting probe for new gauge forces and are characterized by events with boosted lepton jets. Existing techniques are efficient in searching for muonic lepton jets but due to substantial backgrounds have difficulty constraining lepton jets containing only electrons. This is unfortunate since upcoming intensity frontier experiments are sensitive to dark photon masses which only allow electron decays. Analyzing a recently proposed model of kinetic mixing, with new scalar particles decaying into dark photons, we find that existing techniques for electron jets can be substantially improved. We show that using lepton-jet-substructure variables, in association with a boosted decision tree, improves background rejection, significantly increasing the LHC’s reach for dark photons in this region of parameter space.

We discuss the feasibility of detecting the gauge boson of the $U(1{)}_{L_{\mu }-L_{\tau }}$ symmetry, which possesses a mass in the range between MeV and GeV, at the Belle-II experiment. The kinetic mixing between the new gauge boson $Z^{\prime }$ and photon is forbidden at the tree level and is radiatively induced. The leptonic force mediated by such a light boson is motivated by the discrepancy in muon anomalous magnetic moment and also the gap in the energy spectrum of cosmic neutrino. Defining the process $e^{+}{e}^{-}\to \gamma Z^{\prime }\to \gamma \nu \overline{\nu }$ (missing energy) to be the signal, we estimate the numbers of the signal and the background events and show the parameter region to which the Belle-II experiment will be sensitive. The signal process in the $L_{\mu }-L_{\tau }$ model is enhanced with a light $Z^{\prime }$, which is a characteristic feature differing from the dark photon models with a constant kinetic mixing. We find that the Belle-II experiment with the design luminosity will be sensitive to the $Z^{\prime }$ with the mass $M_{Z^{\prime }}\lesssim 1\mathrm{GeV}$ and the new gauge coupling $g_{Z^{\prime }}\gtrsim 8\times {10}^{-4}$, which covers a half of the unconstrained parameter region that explains the discrepancy in muon anomalous magnetic moment. The possibilities to improve the significance of the detection are also discussed.

We calculated the QCD equation of state using Taylor expansions that include contributions from up to sixth order in the baryon, strangeness and electric charge chemical potentials. Calculations have been performed with the Highly Improved Staggered Quark action in the temperature range $T\in [135\mathrm{MeV},330\mathrm{MeV}]$ using up to four different sets of lattice cutoffs corresponding to lattices of size $N_{\sigma }^3\times N_{\tau }$ with aspect ratio $N_{\sigma }/N_{\tau }=4$ and $N_{\tau }=6-16$. The strange quark mass is tuned to its physical value, and we use two strange to light quark mass ratios $m_s/m_l=20$ and 27, which in the continuum limit correspond to a pion mass of about 160 and 140 MeV, respectively. Sixth-order results for Taylor expansion coefficients are used to estimate truncation errors of the fourth-order expansion. We show that truncation errors are small for baryon chemical potentials less then twice the temperature (${\mu }_B\le 2T$). The fourth-order equation of state thus is suitable for the modeling of dense matter created in heavy ion collisions with center-of-mass energies down to $\sqrt{s_{NN}}\sim 12\mathrm{GeV}$. We provide a parametrization of basic thermodynamic quantities that can be readily used in hydrodynamic simulation codes. The results on up to sixth-order expansion coefficients of bulk thermodynamics are used for the calculation of lines of constant pressure, energy and entropy densities in the $T\text{−}{\mu }_B$ plane and are compared with the crossover line for the QCD chiral transition as well as with experimental results on freeze-out parameters in heavy ion collisions. These coefficients also provide estimates for the location of a possible critical point. We argue that results on sixth-order expansion coefficients disfavor the existence of a critical point in the QCD phase diagram for ${\mu }_B/T\le 2$ and $T/T_c({\mu }_B=0)>0.9$.

Nowadays neutrino physics is undergoing a change of perspective: the discovery period is almost over and the phase of precise measurements is starting. Despite the limited statistics collected for some variables, the three–flavor oscillation neutrino framework is strengthening well. In this framework a new method has been developed to determine the neutrino mass ordering, one of the still unknown and most relevant parameters. The method is applied to the 2015 results of the NOvA experiment for ${\nu }_{\mu }\to {\nu }_e$ appearance, including its systematic errors. A substantial gain in significance is obtained compared to the traditional $\mathrm{\Delta }{\chi }^2$ approach. Perspectives are provided for future results obtainable by NOvA with larger exposures. Assuming the number of the 2015 ${\nu }_e$ observed events scales with the exposure, an increase in only a factor three would exclude the inverted hierarchy at more than 95% C.L. over the full range of the $CP$ violating phase. The preliminary 2016 NOvA measurement on ${\nu }_{\mu }\to {\nu }_e$ appearance has also been analyzed.

In this paper, we discuss tensor network descriptions of $\mathrm{AdS}/\mathrm{CFT}$ from two different viewpoints. First, we start with a Euclidean path-integral computation of ground state wave functions with a UV cutoff. We consider its efficient optimization by making its UV cutoff position dependent and define a quantum state at each length scale. We conjecture that this path integral corresponds to a time slice of anti–de Sitter (AdS) spacetime. Next, we derive a flow of quantum states by rewriting the action of Killing vectors of ${\mathrm{AdS}}_3$ in terms of the dual two-dimensional conformal field theory (CFT). Both approaches support a correspondence between the hyperbolic time slice ${\mathrm{H}}_2$ in ${\mathrm{AdS}}_3$ and a version of continuous multiscale entanglement renormalization ansatz. We also give a heuristic argument about why we can expect a sub-AdS scale bulk locality for holographic CFTs.

The quantum renormalization group (QRG) is a realization of holography through a coarse-graining prescription that maps the beta functions of a quantum field theory thought to live on the “boundary” of some space to holographic actions in the “bulk” of this space. A consistency condition will be proposed that translates into general covariance of the gravitational theory in the $D+1$ dimensional bulk. This emerges from the application of the QRG on a planar matrix field theory living on the $D$ dimensional boundary. This will be a particular form of the Wess-Zumino consistency condition that the generating functional of the boundary theory needs to satisfy. In the bulk, this condition forces the Poisson bracket algebra of the scalar and vector constraints of the dual gravitational theory to close in a very specific manner, namely, the manner in which the corresponding constraints of general relativity do. A number of features of the gravitational theory will be fixed as a consequence of this form of the Poisson bracket algebra. In particular, it will require the metric beta function to be of the gradient form.

We present a new mechanism of local scale symmetry breaking based on the scalar density $\mathrm{\Phi }\equiv (1/3!){\epsilon }^{\mu \nu \rho \sigma }{\partial }_{\mu }{A}_{\nu \rho \sigma }\equiv (1/4!){\epsilon }^{\mu \nu \rho \sigma }{F}_{\mu \nu \rho \sigma }^{(0)}$ with an independent third-rank tensor $A_{\mu \nu \rho }$, which replaces the scalar density $\mathrm{\Phi }\equiv {\epsilon }^{\mu \nu \rho \sigma }{\epsilon }_{abcd}({\partial }_{\mu }{\phi }^a)({\partial }_{\nu }{\phi }^b)({\partial }_{\rho }{\phi }^c)({\partial }_{\sigma }{\phi }^d)$ used in “two-measure theory.” We apply this function both to globally and locally scale-invariant systems. For local scale invariance, we modify $F_{\mu \nu \rho \sigma }^{(0)}$ by a certain Chern-Simons term, based on the recently developed tensor-hierarchy formulation. For a locally scale-invariant system with multiple scalars, the minimum value of the potential is realized at exactly zero value, while local scale invariance is broken by some nonzero vacuum expectation values: ${}^{\exists }⟨{\sigma }_i⟩\ne 0$, ${}^{\exists }⟨F_{mnrs}⟩=f_0{\epsilon }_{mnrs}\ne 0$. For these values, the cosmological constant is maintained to be zero, despite the broken local scale invariance.

Using the covariant phase space formalism, we compute the conserved charges for a solution, describing an accelerating and electrically charged Reissner-Nordstrom black hole. The metric is regular provided that the acceleration is driven by an external electric field, in spite of the usual string of the standard C-metric. The Smarr formula and the first law of black hole thermodynamics are fulfilled. The resulting mass has the same form of the Christodoulou-Ruffini irreducible mass. On the basis of these results, we can extrapolate the mass and thermodynamics of the rotating C-metric, which describes a Kerr-Newman-(A)dS black hole accelerated by a pulling string.

Weyl conformal symmetry can solve the problem the spacetime singularities present in Einstein’s gravity. In a recent paper, two of us have found a singularity-free rotating black hole solution in conformal gravity. In addition to the mass $M$ and the spin angular momentum $J$ of the black hole, the new solution has a new parameter, $L$, which here we consider to be proportional to the black hole mass. Since the solution is conformally equivalent to the Kerr metric, photon trajectories are unchanged, while the structure of an accretion disk around a black hole is affected by the value of the parameter $L$. In this paper, we show that x-ray data of astrophysical black holes require $L/M<1.2$.

We prove that the initial value problem for force-free electrodynamics in Euler variables is not well posed. We establish this result by showing that a well-posedness criterion provided by Kreiss fails to hold for this theory, and using a theorem provided by Strang. To show the nature of the problem we display a particular bounded (in Sobolev norms) sequence of initial data for the force-free equations such that at any given time as close to zero as one wishes, the corresponding evolution sequence is not bounded. Thus, the force-free evolution is noncontinuous in that norm with respect to the initial data. We furthermore prove that this problem is also ill-posed in the Leray-Ohya sense.

We study the impact of effective interactions onto relationally evolving group field theory (GFT) condensates based on real-valued fields. In a first step we show that a free condensate configuration in an isotropic restriction settles dynamically into a low-spin configuration of the quantum geometry. This goes hand in hand with the accelerated and exponential expansion of its volume, as well as the vanishing of its relative uncertainty which suggests the classicalization of the quantum geometry. The dynamics of the emergent space can then be given in terms of the classical Friedmann equations. In contrast to models based on complex-valued fields, solutions avoiding the singularity problem can only be found if the initial conditions are appropriately chosen. We then turn to the analysis of the influence of effective interactions on the dynamics by studying in particular the Thomas-Fermi regime. In this context, at the cost of fine-tuning, an epoch of inflationary expansion of quantum geometric origin can be implemented. Finally, and for the first time, we study anisotropic GFT condensate configurations and show that such systems tend to isotropize quickly as the value of the relational clock grows. This paves the way to a more systematic investigation of anisotropies in the context of GFT condensate cosmology.

We present forecasts for cosmological parameters from future cosmic microwave background (CMB) data measured by the stage-4 (S4) generation of ground-based experiments in combination with large-scale anisotropy data from the PIXIE satellite. We demonstrate the complementarity of the two experiments and focus on science targets that benefit from their combination. We show that a cosmic-variance-limited measurement of the optical depth to reionization provided by PIXIE, with error $\sigma (\tau )=0.002$, is vital for enabling a $5\sigma$ detection of the sum of the neutrino masses when combined with a CMB-S4 lensing measurement and with lower-redshift constraints on the growth of structure and the distance-redshift relation. Parameters characterizing the epoch of reionization will also be tightly constrained; PIXIE’s $\tau$ constraint converts into $\sigma (z_{\mathrm{re}})=0.2$ for the mean time of reionization, and a kinematic Sunyaev-Zel’dovich measurement from S4 gives $\sigma (\mathrm{\Delta }{z}_{\mathrm{re}})=0.03$ for the duration of reionization. Both PIXIE and S4 will put strong constraints on primordial tensor fluctuations, vital for testing early-Universe models, and will do so at distinct angular scales. We forecast $\sigma (r)\approx 5\times {10}^{-4}$ for a signal with a tensor-to-scalar ratio $r={10}^{-3}$, after accounting for diffuse foreground removal and delensing. The wide and dense frequency coverage of PIXIE results in an expected foreground-degradation factor on $r$ of only $\approx 25\%$. By measuring large and small scales PIXIE and S4 will together better limit the energy injection at recombination from dark matter annihilation, with $p_{\mathrm{ann}}<0.09\times {10}^{-6}{\mathrm{m}}^3/\mathrm{s}/\text{kg}$ projected at 95% confidence. Cosmological parameters measured from the damping tail with S4 will be best constrained by polarization, which has the advantage of minimal contamination from extragalactic emission.

We argue that ultrahigh-energy cosmic-ray collisions in Earth’s atmosphere can probe the strange quark density of the nucleon. These collisions have center-of-mass energies $\gtrsim 10^{4.6}A\mathrm{GeV}$, where $A\ge 14$ is the nuclear baryon number. We hypothesize the formation of a deconfined thermal fireball which undergoes a sudden hadronization. At production the fireball has a very high matter density and consists of gluons and two flavors of light quarks ($u$, $d$). Because the fireball is formed in the baryon-rich projectile fragmentation region, the high baryochemical potential damps the production of $u\overline{u}$ and $d\overline{d}$ pairs, resulting in gluon fragmentation mainly into $s\overline{s}$. The strange quarks then become much more abundant and upon hadronization the relative density of strange hadrons is significantly enhanced over that resulting from a hadron gas. Assuming the momentum distribution functions can be approximated by Fermi-Dirac and Bose-Einstein statistics, we estimate a kaon-to-pion ratio of about 3 and expect a similar (total) baryon-to-pion ratio. We show that, if this were the case, the excess of strange hadrons would suppress the fraction of energy which is transferred to decaying ${\pi }^0$’s by about 20%, yielding an $\sim 40\%$ enhancement of the muon content in atmospheric cascades, in agreement with recent data reported by the Pierre Auger Collaboration.

With the recent detection of gravitational waves (GWs), marking the start of the new field of GW astronomy, the push for building more sensitive laser-interferometric gravitational wave detectors (GWDs) has never been stronger. Balanced homodyne detection (BHD) allows for a quantum-noise (QN) limited readout of arbitrary light field quadratures, and has therefore been suggested as a vital building block for upgrades to Advanced LIGO and third-generation observatories. In terms of the practical implementation of BHD, we develop a full framework for analyzing the static optical high-order modes (HOMs) occurring in the BHD paths related to the misalignment or mode matching at the input and output ports of the laser interferometer. We find the effects of HOMs on the quantum-noise limited sensitivity is independent of the actual interferometer configuration; e.g. Michelson and Sagnac interferometers are affected in the same way. We show that misalignment of the output ports of the interferometer (output misalignment) only affects the high-frequency part of the quantum-noise limited sensitivity (detection noise). However, at low frequencies, HOMs reduce the interferometer response and the radiation pressure noise (back-action noise) by the same amount and hence the quantum-noise limited sensitivity is not negatively affected in that frequency range. We show that the misalignment of the laser into the interferometer (input misalignment) produces the same effect as output misalignment and additionally decreases the power inside the interferometer. We also analyze dynamic HOM effects, such as beam jitter created by the suspended mirrors of the BHD. Our analyses can be directly applied to any BHD implementation in a future GWD. Moreover, we apply our analytical techniques to the example of the speed meter proof-of-concept experiment under construction in Glasgow. We find that for our experimental parameters, the performance of our seismic isolation system in the BHD paths is compatible with the design sensitivity of the experiment.

We look for long-living topological solutions of classical nonlinear ($1+1$)-dimensional ${\phi }^4$ field theory. To that effect we use the well-known cut-and-match method. In this framework, new long-living states are obtained in both topological sectors. In particular, in one case a highly excited state of a kink is found. We discover several ways of energy reset. In addition to the expected emission of wave packets (with small amplitude), for some selected initial conditions the production of kink-antikink pairs results in a large energy reset. Also, the topological number of a kink in the central region changes in the contrast of conserving full topological number. At lower excitation energies there is a long-living excited vibrational state of the kink; this phenomenon is the final stage of all considered initial states. Over time this excited state of the kink changes to a well-known linearized solution—a discrete kink excitation mode. This method yields a qualitatively new way to describe the large-amplitude bion, which was detected earlier in the kink-scattering processes in the nontopological sector.

In this work, we calculate the $CP$-averaged branching ratios and the direct $CP$-violating asymmetries of the quasi-two-body decays $B_{(s)}\to P(\rho \to )\pi \pi$ by employing the perturbative QCD (PQCD) approach (here $P$ stands for a light pseudoscalar meson $\pi$, $K$, $\eta$ or ${\eta }^{\prime }$). The vector current timelike form factor $F_{\pi }$, which contains the final-state interactions between the pion pair in the resonant region associated with the $P$-wave states $\rho (770)$ along with the two-pion distribution amplitudes, is employed to describe the interactions between the $\rho$ and the pion pair under the hypothesis of the conserved vector current. We found that (a) the PQCD predictions for the branching ratios and the direct $CP$-violating asymmetries for most considered $B_{(s)}\to P(\rho \to )\pi \pi$ decays agree with currently available data within errors, (b) for $\mathcal{B}(B\to {\pi }^0{\rho }^0\to {\pi }^0({\pi }^{+}{\pi }^{-})$, the PQCD prediction is much smaller than the measured one, and (c) for the $B^{+}\to {\pi }^{+}({\rho }^0\to ){\pi }^{+}{\pi }^{-}$ decay mode, there is a negative $CP$ asymmetry $({-27.5}_{-3.7}^{+3.0})\%$, which agrees with other theoretical predictions but is different in sign from those reported by the BABAR and LHCb Collaborations.

Light-by-light scattering sum rules based on general field theory principles relate cross sections with different helicities. In this paper the simplest sum rule is tested for the $I=0$ and 2 channels for “real” photon-photon collisions. Important contributions come from the long-lived pseudoscalar mesons and from dimeson intermediate states. The latest amplitude analysis of $\gamma \gamma \to \pi \pi ,\overline{K}K$ allows this contribution to be evaluated. However, we find that other multimeson contributions up to 2.5 GeV are required to satisfy the sum rules. While data on three- and four-pion cross sections exist, there is no information about their isospin and helicity decomposition. Nevertheless, we show the measured cross sections are sufficiently large to ensure the sum rules for the helicity differences are likely fulfilled.

Thermal corrections to Schwinger pair production are potentially important in particle physics, nuclear physics and cosmology. However, the lowest-order contribution, arising at one loop, has proved difficult to calculate unambiguously. We show that this thermal correction may be calculated for charged scalars using the worldline formalism, where each term in the decay rate is associated with a worldline instanton. We calculate all finite-temperature worldline instantons, their actions and fluctuation prefactors, thus determining the complete one-loop decay rate at finite temperature. The thermal contribution to the decay rate becomes nonzero at a threshold temperature $T=eE/2m$, above which it dominates the zero-temperature result. This is the lowest of an infinite set of thresholds at $T=neE/2m$. The decay rate is singular at each threshold as a consequence of the failure of the quadratic approximation to the worldline path integral. We argue that higher-order effects will make the decay rates finite everywhere and model those effects by the inclusion of hard thermal loop damping rates. We also demonstrate that the formalism developed here generalizes to the case of finite-temperature pair production in inhomogeneous fields.

Any possible Lorentz violation in the hadron sector must be tied to Lorentz violation at the underlying quark level. The relationships between the theories at these two levels are studied using chiral perturbation theory. Starting from a two-flavor quark theory that includes dimension-4 Lorentz-violation operators, the effective Lagrangians are derived for both pions and nucleons, with novel terms appearing in both sectors. Since the Lorentz-violation coefficients for nucleons and pions are all related to a single set of underlying quark coefficients, one can compare the sensitivity of different types of experiments. Our analysis shows that atomic physics experiments currently provide constraints on the quark parameters that are stronger by about 10 orders of magnitude than astrophysical experiments with relativistic pions. Alternatively, it is possible to place approximate bounds on pion Lorentz violation using only proton and neutron observations. Under the assumption that the Lorentz-violating operators considered here are the only ones contributing to the relevant observables and taking the currently unknown hadronic low-energy constants to be of natural size, the resulting estimated bounds on four pion parameters are at the ${10}^{-23}$ level, representing improvements of 10 orders of magnitude.