We investigate whether the six-loop beta function of the $\lambda {\varphi }_4^4$ theory exhibits evidence for an ultraviolet zero. As part of our analysis, we calculate and analyze Padé approximants to this beta function. Extending our earlier results at the five-loop level, we find that in the range of $\lambda$ where the perturbative calculation of the six-loop beta function is reliable, the theory does not exhibit robust evidence for an ultraviolet zero.

Graviton loop corrections to observables in de Sitter space often lead to infrared divergences. We show that these infrared divergences are resolved by the spontaneous breaking of de Sitter invariance.

In this paper we have studied the extended phase space thermodynamics in the canonical ensemble of black holes in massive gravity in anti–de Sitter space. The black holes considered here belong to a theory of massive gravity where the graviton gain a mass due to Lorentz symmetry breaking. We have computed various thermodynamical quantities such as temperature, pressure, Gibbs free energy, and specific heat capacity. The local and the global thermodynamical stability of the black holes are studied in detail. For a specific value of the parameter in the theory, the black holes undergo a first order phase transition similar to the van der Waals phase transitions between gas and liquid under constant temperature. This transition is between the small and the large black holes. The critical exponents are computed at the critical values and shown to be the same as for the van der Waals critical exponents.

The Einstein equivalence principle (EEP) can be verified by the measurement of the spectral distortions of the cosmic microwave background (CMB). One of the consequences of the EEP on cosmological scales is the energy independency of the cosmological redshift effect. We propose a new test of the energy independency of the redshift effect by the measurement of the spectral distortion of CMB. In general relativity, the energy independency of the redshift effect is ensured by the Friedmann-Robertson-Walker (FRW) metric which does not depend on energy. We show that the CMB spectral distortions arise when the FRW metric has the energy dependence. Assuming the simple energy-dependent form of the FRW metric, we evaluate the CMB distortions. From the COBE/FIRAS bound, we find that the deviation degree from the EEP is, at least, less than ${10}^{-5}$ at the CMB energy scales.

The universality of free fall and the weak equivalence principle, which are at the basis of general relativity, have been confirmed to 1 part in $10^{13}$. Space experiments with macroscopic test masses of different composition orbiting Earth inside a low altitude satellite aim to improve this precision by 2 orders of magnitude (with the Microscope satellite launched on April 25, 2016) and up to 4 orders of magnitude (with the Galileo Galilei satellite). At such a high precision, many tiny effects must be taken into account in order to be ruled out as the source of a spurious violation signal. In this work, we investigate the general relativistic effects, including those which involve the rotation of both Earth and the test masses, and show that they are by far too small to be considered even in the most challenging experiment.

The growth index of matter fluctuations is computed for ten distinct accelerating cosmological models and confronted by the latest growth-rate data via a two-step process. First, we implement a joint statistical analysis in order to place constraints on the free parameters of all models using solely background data. Second, using the observed growth rate of clustering from various galaxy surveys we test the performance of the current cosmological models at the perturbation level while either marginalizing over ${\sigma }_8$ or having it as a free parameter. As a result, we find that at a statistical level, i.e., after considering the best-fit ${\chi }^2$ or the value of the Akaike information criterion, most models are in very good agreement with the growth-rate data and are practically indistinguishable from $\mathrm{\Lambda }\mathrm{CDM}$. However, when we also consider the internal consistency of the models by comparing the theoretically predicted values of $({\gamma }_0,{\gamma }_1)$, i.e., the value of the growth index $\gamma (z)$ and its derivative today, with the best-fit ones, we find that the predictions of three out of ten dark energy models are in mild tension with the best-fit ones when ${\sigma }_8$ is marginalized over. When ${\sigma }_8$ is free we find that most models are not only in mild tension, but also predict low values for ${\sigma }_8$. This could be attributed to either a systematic problem with the growth-rate data or the emergence of new physics at low redshifts, with the latter possibly being related to the well-known issue of the lack of power at small scales. Finally, by utilizing mock data based on an large synoptic survey telescope-like survey we show that with future surveys and by using the growth index parametrization, it will be possible to resolve the issue of the low ${\sigma }_8$ but also the tension between the fitted and theoretically predicted values of $({\gamma }_0,{\gamma }_1)$.

We report results of an all-sky search for periodic gravitational waves with frequency between 50 and 510 Hz from isolated compact objects, e.g., neutron stars. A new hierarchical multistage approach is taken, supported by the computing power of the Einstein@Home project, allowing us to probe more deeply than ever before. 16 million subthreshold candidates from the initial search [LIGO Scientific and Virgo Collaborations, Phys. Rev. D 94, 102002 (2016)] are followed up in four stages. None of those candidates is consistent with an isolated gravitational wave emitter, and 90% confidence level upper limits are placed on the amplitudes of continuous waves from the target population. Between 170.5 and 171 Hz, we set the most constraining 90% confidence upper limit on the strain amplitude $h_0$ at $4.3\times {10}^{-25}$, while at the high end of our frequency range, we achieve an upper limit of $7.6\times {10}^{-25}$. These are the most constraining all-sky upper limits to date and constrain the ellipticity of rotating compact objects emitting at 300 Hz at a distance $D$ to less than $6\times {10}^{-7}$ $[\frac{D}{100\mathrm{pc}}]$.

Scalar fields coupled to the Gauss-Bonnet invariant evade the known no-hair theorems and have nontrivial configurations around black holes. We focus on a scalar field that couples linearly to the Gauss-Bonnet invariant and hence exhibits shift symmetry. We study its dynamical evolution and the formation of scalar hair in a Schwarzschild background. We show that the evolution eventually settles to the known static hairy solutions in the appropriate limit.

We investigate baryon number fluctuations for finite temperature and density in two-flavor QCD. This is done within a QCD-improved low-energy effective theory in an extension of the approach put forward by Fu and Pawlowski [Phys. Rev. D 92, 116006 (2015) and Phys. Rev. D 93, 091501 (2016)]. In the present work, we aim to improve the predictive power of this approach for large temperatures and, in partitular, large densities, that is, for small collision energies. This is achieved by taking into account the full frequency dependence of the quark dispersion. This ensures the necessary Silver Blaze property of finite density QCD for the first time, which so far was only implemented approximately. Moreover, we show that Polyakov-loop fluctuations have a sizeable impact at large temperatures and density. The results for the kurtosis of baryon number fluctuations are compared to previous effective theory results, lattice results, and recent experimental data from STAR.

After the Higgs boson discovery, it was established that the Higgs mechanism explains electroweak symmetry breaking and generates the masses of all particles in the Standard Model, with the possible exception of neutrino masses. The hierarchies among fermion masses and mixing angles, however, remain unexplained. We propose a new class of two Higgs doublet models in which a flavor symmetry broken at the electroweak scale addresses this problem. The models are strongly constrained by electroweak precision tests and the fact that they produce modifications to Higgs couplings and flavor-changing neutral currents; they are also constrained by collider searches for extra scalar bosons. The surviving models are very predictive, implying unavoidable new physics signals at the CERN Large Hadron Collider, e.g., extra Higgs bosons with masses $M<700\mathrm{GeV}$.

Recent data from the ATLAS and CMS detectors at the Large Hadron Collider at CERN give a hint of possible violation of flavor in the leptonic decays of the Higgs boson. In this work we analyze the flavor violating leptonic decays $H_1^0\to l_i{\overline{l}}_j$ ($i\ne j$) within the framework of a minimal supersymmetric standard model extension with a vectorlike leptonic generation. Specifically we focus on the decay mode $H_1^0\to \mu \tau$. The analysis is done including tree and loop contributions involving exchange of $W$, $Z$, charged and neutral Higgs bosons and leptons and mirror leptons, charginos and neutralinos and sleptons and mirror sleptons. It is found that a substantial branching ratio of $H_1^0\to \mu \tau$, i.e., of as much as $\mathcal{O}(1)\%$, can be achieved in this model, the size hinted by the ATLAS and CMS data. The flavor violating decays $H_1^0\to e\mu$, $e\tau$ are also analyzed and found to be consistent with the current experimental limits. An analysis of the dependence of flavor violating decays on $CP$ phases is given. The analysis is extended to include flavor decays of the heavier Higgs bosons. A confirmation of the flavor violation in Higgs boson decays with more data that is expected from LHC at $\sqrt{s}=13\mathrm{TeV}$ will be evidence of new physics beyond the standard model.

We discuss the dynamical $\mathrm{D}p$-brane solutions describing any number of $\mathrm{D}p$ branes whose relative orientations are given by certain SU(2) rotations. These are the generalization of the static angled $\mathrm{D}p$-brane solutions. We study the collision of the dynamical D3 brane with angles in type-II string theory, and show that the particular orientation of the smeared D3-brane configuration can provide an example of colliding branes if they have the same charges. Otherwise a singularity appears before D3 branes collide.

Cosmological $\alpha$-attractor models in $\mathcal{N}=1$ supergravity are based on the hyperbolic geometry of a Poincaré disk with the radius square ${\mathcal{R}}^2=3\alpha$. The predictions for the $B$ modes, $r\approx 3\alpha \frac{4}{N^2}$, depend on moduli space geometry and are robust for a rather general class of potentials. Here we notice that starting with M theory compactified on a 7-manifold with $G_2$ holonomy, with a special choice of Betti numbers, one can obtain $d=4$, $\mathcal{N}=1$ supergravity with the rank 7 scalar coset $[\frac{SL(2)}{SO(2)}{]}^7$. In a model where these seven unit size Poincaré disks have identified moduli one finds that $3\alpha =7$. Assuming that the moduli space geometry of the phenomenological models is inherited from this version of M theory, one would predict $r\approx {10}^{-2}$ for $N=53$ $e$-foldings. We also describe the related maximal supergravity and M/string theory models leading to preferred values $3\alpha =1$, 2, 3, 4, 5, 6, 7.

In this work, we study the boson stars and boson shells in a theory involving massive complex scalar fields coupled to the U(1) gauge field and gravity in a conical potential in the presence of a cosmological constant $\mathrm{\Lambda }$ which we treat as a free parameter taking positive and negative values and thereby allowing us to study the theory in the de Sitter and anti-de Sitter spaces respectively. Boson stars are found to come in two types, having either ball-like or shell-like charge density. We have studied the properties of these solutions and have also determined their domains of existence for some specific values of the parameters of the theory. Similar solutions have also been obtained by Kleihaus et al. in a theory involving massless complex scalar fields coupled to the U(1) gauge field and gravity in a conical potential in the absence of a cosmological constant $\mathrm{\Lambda }$.

Seesaw models with leptonic symmetries allow right-handed (RH) neutrino masses at the electroweak scale, or even lower, at the same time having large Yukawa couplings with the Standard Model leptons, thus yielding observable effects at current or near-future lepton-flavor-violation (LFV) experiments. These models have been previously considered also in connection to low-scale leptogenesis, but the combination of observable LFV and successful leptogenesis has appeared to be difficult to achieve unless the leptonic symmetry is embedded into a larger one. In this paper, instead, we follow a different route and consider a possible connection between large LFV rates and dark matter (DM). We present a model in which the same leptonic symmetry responsible for the large Yukawa couplings guarantees the stability of the DM candidate, identified as the lightest of the RH neutrinos. The spontaneous breaking of this symmetry, caused by a Majoron-like field, also provides a mechanism to produce the observed relic density via the decays of the latter. The phenomenological implications of the model are discussed, finding that large LFV rates, observable in the near-future $\mu \to e$ conversion experiments, require the DM mass to be in the keV range. Moreover, the active-neutrino coupling to the Majoron-like scalar field could be probed in future detections of supernova neutrino bursts.

A Chern-Simons theory in 3D is accomplished by the so-called $\theta$ term in the action $(\theta /2)\int F\wedge F$, which contributes only to observable effects on the boundaries of such a system. When electromagnetic radiation interacts with the system, the wave is reflected and its polarization is rotated at the interface, even when both the $\theta$ system and the environment are pure vacuum. These topics have been studied extensively. Here, we investigate the optical properties of a thin $\theta$ film, where multiple internal reflections could interfere coherently. The cases of pure vacuum and a material with magnetoelectric properties are analyzed. It is found that the film reflectance is enhanced compared to ordinary non-$\theta$ systems and the interplay between magnetoelectric properties and the $\theta$ parameter yield film opacity and polarization properties which could be interesting in the case of topological insulators, among other topological systems.

We express the Einstein-Vlasov system in spherical symmetry in terms of a dimensionless momentum variable $z$ (radial over angular momentum). This regularizes the limit of massless particles, and in that limit allows us to obtain a reduced system in independent variables $(t,r,z)$ only. Similarly, in this limit the Vlasov density function $f$ for static solutions depends on a single variable $Q$ (energy over angular momentum). This reduction allows us to show that any given static metric that has vanishing Ricci scalar, is vacuum at the center and for $r>3M$ and obeys certain energy conditions uniquely determines a consistent $f=\overline{k}(Q)$ (in closed form). Vice versa, any $\overline{k}(Q)$ within a certain class uniquely determines a static metric (as the solution of a system of two first-order quasilinear ordinary differential equations). Hence the space of static spherically symmetric solutions of the Einstein-Vlasov system is locally a space of functions of one variable. For a simple two-parameter family of functions $\overline{k}(Q)$, we construct the corresponding static spherically symmetric solutions, finding that their compactness is in the interval $0.7\lesssim {\max }_{\mathrm{r}}(2\mathrm{M}/\mathrm{r})\le 8/9$. This class of static solutions includes one that agrees with the approximately universal type-I critical solution recently found by Akbarian and Choptuik (AC) in numerical time evolutions. We speculate on what singles it out as the critical solution found by fine-tuning generic data to the collapse threshold, given that AC also found that all static solutions are one-parameter unstable and sit on the threshold of collapse.

We study the efficiency of nonspinning waveform templates in gravitational wave searches for aligned-spin binary black holes (BBHs). We use PhenomD, which is the most recent phenomenological waveform model designed to generate the full inspiral-merger-ringdown waveforms emitted from BBHs with the spins aligned with the orbital angular momentum. Here, we treat the effect of aligned-spins with a single spin parameter $\chi$. We consider the BBH signals with moderately small spins in the range of $-0.4\le \chi \le 0.4$. Using nonspinning templates, we calculate fitting factors of the aligned-spin signals in a wide mass range up to $\sim 100M_{\odot }$. We find that the range in spin over which the nonspinning bank has fitting factors exceeding the threshold of 0.965 for all signals in our mass range is very narrow, i.e., $-0.3\le \chi \le 0$. The signals with negative spins can have higher fitting factors than those with positive spins. If $\chi =0.3$, only the highly asymmetric-mass signals can have the fitting factors exceeding the threshold, while the fitting factors for all of the signals can be larger than the threshold if $\chi =-0.3$. We demonstrate that the discrepancy between the regions of a positive and a negative spin is due to the physical boundary ($\eta \le 0.25$) of the template parameter space. In conclusion, we emphasize the necessity of an aligned-spin template bank in the current Advanced LIGO searches for aligned-spin BBHs. We also show that the recovered mass parameters can be significantly biased from the true parameters.