I study the entanglement entropy (EE) across a deformed sphere in conformal field theories (CFTs). I show that the sphere (locally) minimizes the universal term in EE among all shapes. In the work of Allais and Mezei [Phys. Rev. D 91, 046002 (2015)] it was derived that the sphere is a local extremum, by showing that the contribution linear in the deformation parameter is absent. In this paper I demonstrate that the quadratic contribution is positive and is controlled by the coefficient of the stress tensor two-point function, $C_T$. Such a minimization result contextualizes the fruitful relation between the EE of a sphere and the number of degrees of freedom in field theory. I work with CFTs with gravitational duals, where all higher curvature couplings are turned on. These couplings parametrize conformal structures in stress tensor $n$-point functions; hence I show the result for infinitely many CFT examples.

We study the baby Skyrme model as a theory that interpolates between two distinct BPS systems. For this, a near-BPS approximation can be used when there is a small deviation from each of the two BPS limits. We provide analytical explanation and numerical support for the validity of this approximation. We then study the set of all possible supersymmetric extensions of the baby Skyrme model with $\mathcal{N}=1$ and the particular ones with extended $\mathcal{N}=2$ supersymmetries and relate this to the above mentioned almost-BPS approximation.

Supermassive black hole binaries, cosmic strings, relic gravitational waves from inflation, and first-order phase transitions in the early Universe are expected to contribute to a stochastic background of gravitational waves in the $10^{-9}–10^{-7}\mathrm{H}\mathrm{z}$ frequency band. Pulsar timing arrays (PTAs) exploit the high-precision timing of radio pulsars to detect signals at such frequencies. Here we present a time-domain implementation of the optimal cross-correlation statistic for stochastic background searches in PTA data. Due to the irregular sampling typical of PTA data as well as the use of a timing model to predict the times of arrival of radio pulses, time-domain methods are better-suited for gravitational-wave data analysis of such data. We present a derivation of the optimal cross-correlation statistic starting from the likelihood function, a method to produce simulated stochastic background signals, and a rigorous derivation of the scaling laws for the signal-to-noise ratio of the cross-correlation statistic in the two relevant PTA regimes: the weak-signal limit where instrumental noise dominates over the gravitational-wave signal at all frequencies, and a second regime where the gravitational-wave signal dominates at the lowest frequencies.

The stability of Reissner-Nordström black holes under the influence of neutral perturbation fields was proved by Moncrief four decades ago. However, the superradiant scattering phenomenon, which characterizes the dynamics of charged bosonic fields in these charged black-hole spacetimes, imposes a greater and nontrivial threat on their stability. According to this well-known phenomenon, integer-spin charged fields interacting with a Reissner-Nordström black hole can be amplified (gain energy) by extracting some of the black-hole Coulomb energy. If, in addition to being electrically charged, the incident bosonic fields also possess nonzero rest masses, then the mutual gravitational attraction between the central black hole and the fields may prevent the extracted energy and electric charge from escaping to infinity. One may suspect that the physical mechanism of superradiant amplification of charged bosonic fields in the charged Reissner-Nordström black-hole spacetime, when combined with the confinement mechanism provided by the mutual gravitational attraction between the black hole and the massive fields, may lead to a superradiant instability of the Reissner-Nordström black-hole spacetime. (This suspicion is mainly based on our experience with rotating Kerr black holes, which are known to be characterized by an analogous superradiant instability when coupled to massive bosonic fields.) However, in this paper we show that, for highly-charged Reissner-Nordström black holes in the charge interval $8/9<{(Q/M)}^2<1$, the two physical mechanisms which are required in order to trigger the superradiant instability phenomenon in the black-hole spacetime [namely: (1) the superradiant amplification of incident charged scalar fields by the charged black hole, and (2) the existence of a binding potential well in the black-hole exterior region which prevents the extracted energy and electric charge from escaping to infinity] cannot operate simultaneously. In particular, we shall prove that, in the superradiant regime, there is no trapping potential well in the black-hole exterior region. Our stability results for the highly-charged Reissner-Nordström black holes in the regime $8/9<(Q/M{)}^2<1$, combined with former analytical studies which explored the stability of these charged black holes in the complementary regime ${(Q/M)}^2\le 8/9$, establish the fact that charged Reissner-Nordström black holes are stable to charged massive scalar perturbations in the entire parameter space.

We examine a one-parameter family of analytical solutions representing spherically symmetric collapse of a nonlinear massless scalar field with self-interaction in an asymptotically flat spacetime. The time evolution exhibits a type of critical behavior. Depending on the scalar charge parameter $q$ as compared to a critical value $q^{*}$, the incoming scalar wave collapses either to a globally naked central singularity if $q<q^{*}$ (weak field) or to a scalar-hairy black hole if $q>q^{*}$ (strong field), both having finite asymptotic masses. Near the critical evolution, the black hole mass follows a product-logarithmic scaling law: $-M^2\ln M\sim q-q^{*}$ with $0<M\ll 1$ and $q>q^{*}$. The solution admits no self-similarity and satisfies the null and the strong energy conditions.

Recent studies show that an intermediate mass black hole (IMBH) may develop a dark matter (DM) minihalo according to some BH formation scenarios. We consider a binary system composed of an IMBH surrounded by a DM minispike and a stellar mass object orbiting around the IMBH. The binary evolves due to gravitational pull and dynamical friction from the DM minispike and backreaction from its gravitational wave (GW) radiation which can be detected by future space-borne GW experiments such as eLISA/NGO. We consider a single power-law model for the DM minispike which is assumed to consist of nonannihilating DM particles and derive GW waveforms including the DM effects analytically. We demonstrate that a detection of GWs from such a binary with eLISA/NGO is affected by the DM effects and enables us to measure the DM minispike parameters accurately. For instance, in our reference case originally advocated by Zhao and Silk [Phys. Rev. Lett. 95, 011301 (2005)] and Bertone et al. [Phys. Rev. D 72, 103517 (2005)], we could determine the power-law index $\alpha$ of the DM minispike radial profile with a $1\sigma$ relative error of $\pm 5\times 10^{-6}$ for a GW signal with signal-to-noise ratio 10 and assuming a five-year observation with eLISA. We also investigate how accurately the DM parameters can be determined for various values of the slope of the DM minispike and the masses of the IMBH–stellar mass object binary surrounded by the DM minispike. We find that the power-law index $\alpha$ is measurable at 10% level even for a slightly flatter radial distribution of $\alpha \sim 1.7$. We clarify that the larger masses of the IMBH and the stellar object lead to the worse measurement accuracies of the DM parameters because the number of GW cycles becomes smaller.

We propose an (optimal) estimator for a CMB bispectrum containing logarithmically spaced oscillations. There is tremendous theoretical interest in such bispectra, and they are predicted by a plethora of models, including axion monodromy models of inflation and initial state modifications. The number of resolved logarithmical oscillations in the bispectrum is limited due to the discrete resolution of the multipole bispectrum. We derive a simple relation between the maximum number of resolved oscillations and the frequency. We investigate several ways to factorize the primordial bispectrum, and conclude that a one-dimensional expansion in the sum of the momenta $\sum k_i=k_t$ is the most efficient and flexible approach. We compare the expansion to the exact result in multipole space and show for ${\omega }_{\text{eff}}=100$ that $\mathcal{O}(10^3)$ modes are sufficient for an accurate reconstruction. We compute the expected ${\sigma }_{f_{\mathrm{NL}}}$ and find that within an effective field theory (EFT) the overall signal to noise scales as $S/N\propto {\omega }^{3/2}$. Using only the temperature data we find $S/N\sim \mathcal{O}(1–10^2)$ for the frequency domain set by the EFT.

Future galaxy redshift surveys aim at probing the clustering of the cosmic large-scale structure with unprecedented accuracy, thus complementing cosmic microwave background experiments in the quest to deliver the most precise and accurate picture ever of our Universe. Analyses of such measurements are usually performed within the context of the so-called vanilla $\mathrm{\Lambda }\mathrm{CDM}$ model—the six-parameter phenomenological model which, for instance, emerges from best fits against the recent data obtained by the Planck satellite. Here, we show that such an approach is prone to subtle systematics when the Gaussianity of primordial fluctuations is concerned. In particular, we demonstrate that, if we neglect even a tiny amount of primordial non-Gaussianity—fully consistent with current limits—we shall introduce spurious biases in the reconstruction of cosmological parameters. This is a serious issue that must be properly accounted for in view of accurate (as well as precise) cosmology.

We examine the cosmological consequences of an alternative to the standard expression for bulk viscosity, one which was proposed to avoid the propagation of superluminal signals without the necessity of extending the space of variables of the theory. The Friedmann equation is derived for this case, along with an expression for the effective pressure. We find solutions for the evolution of the density of a viscous component, which differs markedly from the case of conventional Eckart theory; our model evolves toward late-time phantomlike behavior with a future singularity. Entropy production is addressed, and some similarities and differences to approaches based on the Mueller-Israel-Stewart theory are discussed.

We discuss the future detectability of gravitational-wave induced lensing from high-sensitivity cosmic microwave background (CMB) experiments. Gravitational waves can induce a rotational component of the weak-lensing deflection angle, usually referred to as the curl mode, which would be imprinted on the CMB maps. Using the technique of reconstructing lensing signals involved in CMB maps, this curl mode can be measured in an unbiased manner, offering an independent confirmation of the gravitational waves complementary to B-mode polarization experiments. Based on the Fisher matrix analysis, we first show that with the noise levels necessary to confirm the consistency relation for the primordial gravitational waves, the future CMB experiments will be able to detect the gravitational-wave induced lensing signals. For a tensor-to-scalar ratio of $r\lesssim 0.1$, even if the consistency relation is difficult to confirm with a high significance, the gravitational-wave induced lensing will be detected at more than $3\sigma$ significance level. Further, we point out that high-sensitivity experiments will be also powerful to constrain the gravitational waves generated after the recombination epoch. Compared to the B-mode polarization, the curl mode is particularly sensitive to gravitational waves generated at low redshifts ($z\lesssim 10$) with a low frequency ($k\lesssim 10^{-3}{\mathrm{Mpc}}^{-1}$), and it could give a much tighter constraint on their energy density ${\mathrm{\Omega }}_{\mathrm{GW}}$ by more than 3 orders of magnitude.

Introducing constant background fields into the noncommutative gauge theory, we first obtain a Hermitian fermion Lagrangian which involves a Lorentz violation term, then we generalize it to a new deformed canonical noncommutation relations for fermion field. Massless neutrino oscillation in the deformed canonical noncommutation relations is analyzed. The restriction of the noncommutative coefficients is also discussed. By comparing with the existing experimental data of conventional neutrino oscillations, the order of noncommutative deformed coefficients is given from different ways.

For a heavy Higgs boson above the $t\overline{t}$ threshold we consider three decay modes that could compete with decay to $t\overline{t}$, even in the alignment limit of a 2-Higgs doublet model. The decays $H\to AZ$, $Z^{\prime }{Z}^{\prime }$ and ${\tau }^{\prime }{\tau }^{\prime }$ show that heavy Higgs decays can be an effective probe of new physics both within and beyond this model.

We show that a standard model gauge singlet fermion field, with mass of order keV or larger, and involved in the inverse seesaw mechanism of light neutrino mass generation, can be a good warm dark matter candidate. Our framework is based on $B-L$ extension of the standard model. The construction ensures the absence of any mixing between active neutrinos and the aforementioned dark matter field. This circumvents the usual constraints on the mass of warm dark matter imposed by x-ray observations. We show that an overabundance of thermally produced warm dark matter (which nevertheless does not reach chemical equilibrium) can be reduced to an acceptable range in the presence of a moduli field decaying into radiation—though only when the reheat temperature is low enough. Our warm dark matter candidate can also be produced directly from the decay of the moduli field during reheating. In this case, obtaining the right amount of relic abundance, while keeping the reheat temperature high enough as to be consistent with big bang nucleosynthesis bounds, places constraints on the branching ratio for the decay of the moduli field into dark matter.

Distinguishing hadronically decaying boosted top quarks from massive QCD jets is an important challenge at the Large Hadron Collider. In this paper we use the power-counting method to study jet substructure observables designed for top tagging, and gain insight into their performance. We introduce a powerful new family of discriminants formed from the energy correlation functions which outperform the widely used $N$-subjettiness. These observables take a highly nontrivial form, demonstrating the importance of a systematic approach to their construction.

We analyze fermionic response in the geometry holographically dual to zero-temperature $\mathcal{N}=4$ super-Yang-Mills theory with two equal nonvanishing chemical potentials, which is characterized by a singular horizon and zero ground state entropy. We show that fermionic fluctuations are completely stable within a gap in energy around a Fermi surface singularity, beyond which non-Fermi liquid behavior returns. This gap disappears abruptly once the final charge is turned on and is associated to a discontinuity in the corresponding chemical potential. We also show that the singular near-horizon geometry lifts to a smooth ${\mathrm{AdS}}_3\times {\mathbb{R}}^3$ and interpret the gap as a region where the quasiparticle momentum is spacelike in six dimensions due to the momentum component in the Kaluza-Klein direction, corresponding to the final charge.

We derive the polarization tensor of graphene at nonzero temperature in $(2+1)$-dimensional space-time. The obtained tensor coincides with the previously known result at all Matsubara frequencies, but, in contrast, it admits analytic continuation to the real frequency axis satisfying all physical requirements. Using the obtained representation for the polarization tensor, we develop a quantum field theoretical description for the reflectivity of graphene. The analytic asymptotic expressions for the reflection coefficients and reflectivities at low and high frequencies are derived for both independent polarizations of the electromagnetic field. The dependencies of the reflectivities on the frequency and angle of incidence are investigated. Numerical computations using the exact expressions for the polarization tensor are performed and application regions for the analytic asymptotic results are determined.

Various theoretical and experimental considerations motivate models with high-scale supersymmetry breaking. While such models may be difficult to test in colliders, we propose looking for signatures at much lower energies. We show that a keV line in the x-ray spectrum of galaxy clusters (such as the recently disputed 3.5-keV observation) can have its origin in a universal string axion coupled to a hidden supersymmetry breaking sector. A linear combination of the string axion and an additional axion in the hidden sector remains light, obtaining a mass of order 10 keV through supersymmetry breaking dynamics. In order to explain the x-ray line, the scale of supersymmetry breaking must be about $10^{11–12}\mathrm{GeV}$. This motivates high-scale supersymmetry as in pure gravity mediation or minimal split supersymmetry and is consistent with all current limits. Since the axion mass is controlled by a dynamical mass scale, this mass can be much higher during inflation, avoiding isocurvature (and domain wall) problems associated with high-scale inflation. In an appendix, we present a mechanism for dilaton stabilization that additionally leads to $\mathcal{O}(1)$ modifications of the gaugino mass from anomaly mediation.

We consider a real massive free quantum scalar field with arbitrary curvature coupling on $n$-dimensional anti–de Sitter spacetime. We use Hadamard renormalization to find the vacuum expectation values of the quadratic field fluctuations and the stress-energy tensor, presenting explicit results for $n=2$ to $n=11$ inclusive.

We discuss a solution of the Einstein equations, obtained by gluing the external Kerr metric and the internal Weyl metric, describing an axisymmetric static vacuum distorted black hole. These metrics are glued at the null surfaces representing their horizons. For this purpose we use the formalism of thin null shells. The corresponding solution is called a “hybrid” black hole. The null shell has an angular momentum which is the origin of the rotation of the external Kerr spacetime. At the same time, the shell distorts the geometry inside the horizon. The inner geometry of the hybrid black hole coincides with the geometry of the interior of a nonrotating Weyl-distorted black hole. Properties of the hybrid black holes are briefly discussed.