We expand the dynamical systems investigation of cosmological scalar fields characterized by kinetic corrections presented in N. Tamanini, Dynamics of cosmological scalar fields, Phys. Rev. D 89, 083521 (2014). In particular we do not restrict the analysis to exponential potentials only, but we consider arbitrary scalar field potentials and derive general results regarding the corresponding cosmological dynamics. Two specific potentials are then used as examples to show how these models can be employed not only to describe dark energy, but also to achieve dynamical crossing of the phantom barrier at late times. Stability and viability issues at the classical level are also discussed.

We provide an anthropic reason for the supersymmetry breaking scale being much higher than the electroweak scale, as indicated by the null result of collider experiments and the observed 125 GeV Higgs boson. We focus on a new inflation model as a typical low-scale inflation model that may be expected in the string landscape. In this model, $R$ symmetry is broken at the minimum of the inflaton potential, and its breaking scale is related to the reheating temperature. Once we admit that the anthropic principle requires thermal leptogenesis, we obtain a lower bound for the gravitino mass, which is related to the $R$ symmetry breaking scale. This scenario and resulting gravitino mass predict the consistent amplitude of density perturbations. We also find that string axions and saxions are consistently implemented in this scenario.

CMS has reported indications ($2.4\sigma$) of the decay of the Higgs boson into $\mu \tau$. The simplest explanation for such a decay would be a general two-Higgs doublet model (2HDM). In this case, one would expect the heavy neutral Higgs bosons, $H$ and $A$, to also decay in a similar manner. We study two specific models. The first is the type III 2HDM, and the second is a 2HDM, originally proposed by Branco et al., in which all flavor-changing neutral processes are given by the weak mixing matrix. In the latter model, since mixing between the second and third generations in the lepton sector is large, flavor-changing interactions are large. In this model, we find that the decays of $H$ and $A$ to $\mu \tau$ can be as high as 60%.

We investigate the behavior under Lorentz transformations of perturbative coefficient functions in a collinear twist-3 formalism relevant for high-energy observables including transverse polarization of hadrons. We argue that those perturbative coefficient functions can, a priori, acquire quite different yet Lorentz-invariant forms in various frames. This somewhat surprising difference can be traced back to a general dependence of the perturbative coefficient functions on light cone vectors which are introduced by the twist-3 factorization formulas and which are frame-dependent. One can remove this spurious frame dependence by invoking so-called Lorentz invariance relations (LIRs) between twist-3 parton correlation functions. Some of those relations for twist-3 distribution functions were discussed in the literature before. In this paper we derive the corresponding LIRs for twist-3 fragmentation functions. We explicitly demonstrate that these LIRs remove the light cone vector dependence by considering transverse spin observables in the single-inclusive production of hadrons in lepton-nucleon collisions, $\ell N\to hX$. With the LIRs in hand, we also show that twist-3 observables in general can be written solely in terms of three-parton correlation functions.

Long-duration gamma-ray bursts (GRBs) have been often considered as the natural evolution of some core-collapse supernovae (SNe). While GRBs with relativistic jets emit an electromagnetic signal, GRBs with mildly relativistic jets are opaque to photons and therefore could be detectable through neutrinos only. We discuss the possibility that successful GRBs and mildly relativistic jets belong to the same class of astrophysical transients with different Lorentz factor ${\mathrm{\Gamma }}_b$ and study the production of high-energy neutrinos as a function of ${\mathrm{\Gamma }}_b$, by including both proton-photon and proton-proton interactions. By assuming a SN-GRB connection, we find that the diffuse neutrino emission from optically thick jets with Lorentz factors lower than the ones of successful GRBs can be one of the main components of the observed IceCube high-energy neutrino flux. Moreover, under the assumption that all these jets belong to the same class of astrophysical transients, we show that the IceCube high-energy neutrino data provide indirect constraints on the rate of nonsuccessful jets, favoring a local rate lower than tens of percent of the local SN rate. These limits are currently comparable to dedicated searches on choked sources and are expected to become tighter with the accumulation of more high-energy neutrino data.

A simple collinearity argument implies that the massless particle three-point function of helicities $h_1,h_2,h_3$ with corresponding real-valued four-momenta $k_1,k_2,k_3$ taken as all incoming or all outgoing (i.e., $k_1+k_2+k_3=0$) vanishes by helicity conservation unless $h_1+h_2+h_3=0$. When any one particle with four-momentum $k$ is off mass shell, this constraint no longer applies; a forbidden amplitude with $h_1+h_2+h_3\ne 0$ on shell can be nonzero off shell, but it vanishes proportionally to $k^2$ as $k$ approaches mass shell. When an on-shell forbidden amplitude is coupled to an allowed $n$-point amplitude to form an $n+1$-point function, this $k^2$ factor in the forbidden amplitude cancels the $k^2$ in the propagator, leading to an $n+1$-point function that has no pole at $k^2=0$. We relate our results for real-valued four-momenta to the corresponding selection rules that have been derived in the on-shell literature for complexified four-momenta.

We show that the two-point function of a quantum field theory with de Sitter momentum space (herein called DSR) can be expressed as the product of a standard delta function and an energy-dependent factor. The proportionality to a standard delta function is a nontrivial result valid in any theory without a preferred frame and relies crucially on the on-shellness condition. Different theories are distinguished by the specific form of the energy-dependent proportionality factor. Applied to models exhibiting running of the dimensionality of space, this result is essential in proving that vacuum fluctuations are generally scale invariant at high energies whenever there is running to two dimensions. This is equally true for theories with and without a preferred frame, with differences arising only as we consider higher order correlators. Specifically, the three-point function of DSR has a unique structure of “open triangles,” as shown here.

Ward identities for Reggeons are studied in the framework of an effective action approach to the QCD in Regge kinematics. It is shown that they require the introduction of new contributions not present in the Reggeon diagrams initially. Application to vertices $\mathrm{RR}\to \mathrm{RP}$ and $\mathrm{RR}\to \mathrm{RRP}$ are considered and diagrams which have to be added to the QCD ones are found.

We study the charged scalar collapse in de Sitter spacetimes. With the electric charge, there is one more competitor to join the competition of dynamics in the gravitational collapse. We find that two factors can influence the electric charge. If we just adjust the charge conjugation, the electric charge effect is always perturbative at the black hole threshold. The electric charge can also be influenced by the initial conditions of perturbations. These initial parameters can be tuned to control the competition in dynamics and present us new and rich physics in the process of gravitational collapse. We give physical explanations of these phenomena found in dynamics. Furthermore we show that the properties of the gravitational collapse we observed do not depend on spacetime dimensions.

The halo model is a theoretically and empirically well-motivated framework for predicting the statistics of the nonlinear matter distribution in the Universe. However, current incarnations of the halo model suffer from two major deficiencies: (i) they do not enforce the stress-energy conservation of matter; (ii) they are not guaranteed to recover exact perturbation theory results on large scales. Here, we provide a formulation of the halo model (EHM) that remedies both drawbacks in a consistent way, while attempting to maintain the predictivity of the approach. In the formulation presented here, mass and momentum conservation are guaranteed on large scales, and results of the perturbation theory and the effective field theory can, in principle, be matched to any desired order on large scales. We find that a key ingredient in the halo model power spectrum is the halo stochasticity covariance, which has been studied to a much lesser extent than other ingredients such as mass function, bias, and profiles of halos. As written here, this approach still does not describe the transition regime between perturbation theory and halo scales realistically, which is left as an open problem. We also show explicitly that, when implemented consistently, halo model predictions do not depend on any properties of low-mass halos that are smaller than the scales of interest.

The energy scale of dark energy, $\sim 2\times {10}^{-3}\mathrm{eV}$, is a long way off compared to all known fundamental scales—except for the neutrino masses. If dark energy is dynamical and couples to neutrinos, this is no longer a coincidence. The time at which dark energy starts to behave as an effective cosmological constant can be linked to the time at which the cosmic neutrinos become nonrelativistic. This naturally places the onset of the Universe’s accelerated expansion in recent cosmic history, addressing the why-now problem of dark energy. We show that these mechanisms indeed work in the growing neutrino quintessence model—even if the fully nonlinear structure formation and backreaction are taken into account, which were previously suspected of spoiling the cosmological evolution. The attractive force between neutrinos arising from their coupling to dark energy grows as large as ${10}^6$ times the gravitational strength. This induces very rapid dynamics of neutrino fluctuations which are nonlinear at redshift $z\approx 2$. Nevertheless, a nonlinear stabilization phenomenon ensures only mildly nonlinear oscillating neutrino overdensities with a large-scale gravitational potential substantially smaller than that of cold dark matter perturbations. Depending on model parameters, the signals of large-scale neutrino lumps may render the cosmic neutrino background observable.

A numerical study of a pseudoscalar inflation having an axion-photon-like coupling is performed by solving numerically the coupled differential equations of motion for inflaton and photon mode functions from the onset of inflation to the end of reheating. The backreaction due to particle production is also included self-consistently. We find that this particular inflation model realizes the idea of a warm inflation in which a steady thermal bath is established by the particle production. In most cases, this thermal bath exceeds the amount of radiation released in the reheating process. In the strong coupling regime, the transition from the inflationary to the radiation-dominated phase does not involve either a preheating nor reheating process. In addition, energy density peaks produced near the end of inflation may lead to the formation of primordial black holes.

We present new, tight, constraints on the cosmological background of gravitational waves (GWs) using the latest measurements of CMB temperature and polarization anisotropies provided by the Planck, BICEP2 and Keck Array experiments. These constraints are further improved when the GW contribution $N_{\mathrm{eff}}^{\mathrm{GW}}$ to the effective number of relativistic degrees of freedom $N_{\mathrm{eff}}$ is also considered. Parametrizing the tensor spectrum as a power law with tensor-to-scalar ratio $r$, tilt $n_{\mathrm{t}}$ and pivot $0.01{\mathrm{Mpc}}^{-1}$, and assuming a minimum value of $r=0.001$, we find $r<0.089$, $n_{\mathrm{t}}=1.7_{-2.0}^{+2.1}$ (95% CL, no $N_{\mathrm{eff}}^{\mathrm{GW}}$) and $r<0.082$, $n_{\mathrm{t}}=-0.05_{-0.87}^{+0.58}$ (95% CL, with $N_{\mathrm{eff}}^{\mathrm{GW}}$). When the recently released 95 GHz data from Keck Array are added to the analysis, the constraints on $r$ are improved to $r<0.067$ (95% CL, no $N_{\mathrm{eff}}^{\mathrm{GW}}$), $r<0.061$ (95% CL, with $N_{\mathrm{eff}}^{\mathrm{GW}}$). We discuss the limits coming from direct detection experiments such as LIGO-Virgo, pulsar timing (European Pulsar Timing Array) and CMB spectral distortions (FIRAS). Finally, we show future constraints achievable from a COrE-like mission: if the tensor-to-scalar ratio is of order $10^{-2}$ and the inflationary consistency relation $n_{\mathrm{t}}=-r/8$ holds, COrE will be able to constrain $n_{\mathrm{t}}$ with an error of 0.16 at 95% CL. In the case that lensing $B$-modes can be subtracted to 10% of their power, a feasible goal for COrE, these limits will be improved to 0.11 at (95% CL).

We investigate a method to assess the validity of gravitational-wave detector calibration through the use of gamma-ray bursts as standard sirens. Such signals, as measured via gravitational-wave observations, provide an estimated luminosity distance that is subject to uncertainties in the calibration of the data. If a host galaxy is identified for a given source then its redshift can be combined with current knowledge of the cosmological parameters yielding the true luminosity distance. This will then allow a direct comparison with the estimated value and can validate the accuracy of the original calibration. We use simulations of individual detectable gravitational-wave signals from binary neutron star (BNS) or neutron star-black hole systems, which we assume to be found in coincidence with short gamma-ray bursts, to estimate any discrepancy in the overall scaling of the calibration for detectors in the Advanced LIGO and Advanced Virgo network. We find that the amplitude scaling of the calibration for the LIGO instruments could on average be confirmed to within $\sim 10\%$ for a BNS source within 100 Mpc. This result is largely independent of the current detector calibration method and gives an uncertainty that is competitive with that expected in the current calibration procedure. Confirmation of the calibration accuracy to within $\sim 20\%$ can be found with BNS sources out to $\sim 500\mathrm{Mpc}$.

The physical origin of the dark energy that causes the accelerated expansion rate of the Universe is one of the major open questions of cosmology. One set of theories postulates the existence of a self-interacting scalar field for dark energy coupling to matter. In the chameleon dark energy theory, this coupling induces a screening mechanism such that the field amplitude is nonzero in empty space but is greatly suppressed in regions of terrestrial matter density. However measurements performed under appropriate vacuum conditions can enable the chameleon field to appear in the apparatus, where it can be subjected to laboratory experiments. Here we report the most stringent upper bound on the free neutron-chameleon coupling in the strongly coupled limit of the chameleon theory using neutron interferometric techniques. Our experiment sought the chameleon field through the relative phase shift it would induce along one of the neutron paths inside a perfect crystal neutron interferometer. The amplitude of the chameleon field was actively modulated by varying the millibar pressures inside a dual-chamber aluminum cell. We report a 95% confidence level upper bound on the neutron-chameleon coupling $\beta$ ranging from $\beta <4.7\times {10}^6$ for a Ratra-Peebles index of $n=1$ in the nonlinear scalar field potential to $\beta <2.4\times {10}^7$ for $n=6$, one order of magnitude more sensitive than the most recent free neutron limit for intermediate $n$. Similar experiments can explore the full parameter range for chameleon dark energy in the foreseeable future.

We compute the normalized structure constant of three twist-2 operators in $\mathcal{N}=4$ SYM in the leading Balitsky-Fadin-Kuraev-Lipatov (BFKL) approximation at any $N_c$. The result is applicable to other gauge theories including QCD.

We calculate holographically arbitrary $n$-point correlators of the boundary stress tensor in three-dimensional Einstein gravity with negative or vanishing cosmological constant. We provide explicit expressions up to 5-point (connected) correlators and show consistency with the Galilean conformal field theory Ward identities and recursion relations of correlators, which we derive. This provides a novel check of flat space holography in three dimensions.

We investigate exclusion limits on the nonuniversal gaugino mass scenario in the minimal supersymmetric standard model (MSSM), according to the latest results of the superparticle search at the LHC8 and the LHC13. In this scenario, suitable ratios of wino to gluino mass can realize the observed value of the Higgs boson mass, while keeping a small $\mu$ parameter. Such a small $\mu$ parameter corresponds to the mass of Higgsino, so that lightest neutralino and chargino are Higgsino-like and their masses are almost degenerate. Besides, we find that the right-handed top squark tends to be lighter than other sfermions and then the top squark search, where the top squark decays to a quark and Higgsino, is relevant to our model. In our analysis, the exclusion limits are derived using the data of the top squark searches in the $bb+E_T^{\mathrm{miss}}$ and $tb+E_T^{\mathrm{miss}}$ channels. Furthermore, the exclusion limit on gluino mass, which is crucial to our scenario, is investigated as well. The analysis of the gluino is based on the data of the analysis with large missing energy and at least three b-tagged jets at the ATLAS experiment.

In this work, we present mass limits on gluinos and stops in a natural next-to-minimal supersymmetric Standard Model with a singlino as the lightest supersymmetric particle. Motivated by naturalness, we consider spectra with light Higgsinos, sub-TeV third generation sparticles and gluinos well below the multi-TeV regime while the electroweak gauginos, the sleptons and the first and second generation squarks are decoupled. We check that our natural supersymmetry spectra satisfy all electroweak precision observables and flavor measurements as well as theoretical constraints. By reinterpreting the results from the 8 TeV ATLAS supersymmetry searches we present the 95% C.L. exclusion limits on the model. The results show that the presence of a singlino lightest supersymmetric particle can lengthen decay chains and soften the final state particle energies. While this does reduce the strength of the bounds in some areas of parameter space, the LHC still displays good sensitivity to the model.

A detailed investigation of finite-size effects is performed for SU(2) gauge theory with two fermions in the adjoint representation, which previous lattice studies have shown to be inside the conformal window. The system is investigated with different spatial and temporal boundary conditions on lattices of various spatial and temporal extensions, for two values of the bare fermion mass representing a heavy and light fermion regime. Our study shows that the infinite-volume limit of masses and decay constants in the mesonic sector is reached only when the mass of the pseudoscalar particle $M_{\mathrm{PS}}$ and the spatial lattice size $L$ satisfy the relation $L{M}_{\mathrm{PS}}\ge 15$. This bound, which is at least a factor of three higher than what is observed in QCD, is a likely consequence of the different spectral signatures of the two theories, with the scalar isosinglet ($0^{++}$ glueball) being the lightest particle in our model. In addition to stressing the importance of simulating large lattice sizes, our analysis emphasizes the need to understand quantitatively the full spectrum of the theory rather than just the spectrum in the mesonic isotriplet sector. While for the lightest fermion measuring masses from gluonic operators proves to be still challenging, reliable results for glueball states are obtained at the largest fermion mass and, in the mesonic sector, for both fermion masses. As a byproduct of our investigation, we perform a finite-size scaling of the pseudoscalar mass and decay constant. The data presented in this work support the conformal behavior of this theory with an anomalous dimension ${\gamma }_{*}\simeq 0.37$.