The unitary moving mirror model is one of the best quantum systems for checking the reasoning of the original firewall paradox of Almheiri et al. [J. High Energy Phys. 02 (2013) 062] in quantum black holes. Though the late-time part of radiations emitted from the mirror is fully entangled with the early part, no firewall exists with a deadly, huge average energy flux in this model. This is because the high-energy entanglement structure of the discretized systems in almost maximally entangled states is modified so as to yield the correct description of low-energy effective field theory. Furthermore, the strong subadditivity paradox of firewalls is resolved using nonlocality of general one-particle states and zero-point fluctuation entanglement. Due to the Reeh-Schlieder theorem in quantum field theory, another firewall paradox is inevitably raised with quantum remote measurements in the model. We resolve this paradox from the viewpoint of the energy cost of measurements. No firewall appears, as long as the energy for the measurement is much smaller than the ultraviolet cutoff scale.

We examine strictly static asymptotically flat spacetimes in Einstein-Gauss-Bonnet gravity with a $U(1)$ gauge field, revealing that, up to small curvature corrections, static conformally flat slices of the spacetime in question are of Minkowski origin. We consider uncharged and charged black hole solutions in the theory, showing that, up to the small curvature limit, they are diffeomorphic to Schwarzschild-Tangherlini or Reissner-Nordström solutions, respectively.

We study the infrared (large separation) behavior of a massless minimally coupled scalar quantum field theory with a quartic self interaction in de Sitter spacetime. We show that the perturbation series in the interaction strength is singular and secular, i.e. it does not lead to a uniform approximation of the solution in the infrared region. Only a nonperturbative resummation can capture the correct infrared behavior. We seek to justify this picture using the Dyson-Schwinger equations in the ladder-rainbow approximation. We are able to write down an ordinary differential equation obeyed by the two-point function and perform its asymptotic analysis. Indeed, while the perturbative series—truncated at any finite order—is growing in the infrared, the full nonperturbative sum can be decaying.

If we posit the validity of the consistency relations, the tensor spectral index and the relative amplitude of the scalar and tensor power spectra are both fixed by a single slow roll parameter. The physics of the protoinflationary transition can explicitly break the consistency relations, causing a reduction of the inflationary curvature scale in comparison with the conventional lore. After critical scrutiny, we argue that the inflationary curvature scale, the total number of inflationary $e$-folds and, ultimately, the excursion of the inflaton across its Planckian boundary are all characterized by a computable theoretical error. While these considerations ease some of the tensions between the Bicep2 data and the other satellite observations, they also demand an improved understanding of the protoinflationary transition whose physical features may be assessed, in the future, through a complete analysis of the spectral properties of the B mode autocorrelations.

The IceCube Neutrino Observatory has observed highly energetic neutrinos in excess of the expected atmospheric neutrino background. It is intriguing to consider the possibility that such events are probing fundamental physics beyond the standard model of particle physics. In this context, $\mathcal{O}(\mathrm{PeV})$ dark matter particles decaying to neutrinos have been considered, while dark matter annihilation has been dismissed invoking the unitarity bound as a limiting factor for the annihilation rate. However, the latter claim was done ignoring the contribution from dark matter substructure, which in a PeV cold dark matter scenario would extend down to a free-streaming mass of $\mathcal{O}(10^{-18}{\mathrm{M}}_{\odot })$. Since the unitarity bound is less stringent at low velocities, $({\sigma }_{\text{ann}}v)\le 4\pi /m_{\chi }^{2}v$, then it is possible that these cold and dense subhalos would contribute dominantly to a dark-matter-induced neutrino flux and easily account for the events observed by IceCube. A dark matter model in which annihilations are enhanced by a Sommerfeld mechanism can naturally support such a scenario. Interestingly, the spatial distribution of the events shows features that would be expected in a dark matter interpretation. Although not conclusive, 9 of the 37 events appear to be clustered around an extended region near the Galactic center, while 6 others spatially coincide, within the reported angular errors, with 5 of 26 Milky Way satellites. However, a simple estimate of the probability of the latter occurring by chance is $\sim 35\%$. More events are needed to statistically test this hypothesis. PeV dark matter particles are massive enough that their abundance as standard thermal relics would overclose the Universe. This issue can be solved in alternative scenarios, for instance, if the decay of new massive unstable particles generates significant entropy reheating the Universe to a slightly lower temperature than the freeze-out temperature, $T_{\mathrm{RH}}\lesssim T_{\mathrm{f}}\sim 4\times 10^4\mathrm{GeV}$.

We give a full investigation on the dynamics of power-law kinetic quintessence $L(X,\varphi )=V(\varphi )(-X+X^2)$ by considering the potential related parameter $\mathrm{\Gamma }(=\frac{V{V}^{\prime \prime }}{{V^{\prime }}^2})$ as a function of another potential parameter $\lambda (=\frac{V^{\prime }}{\kappa V^{3/2}})$, which correspondingly extends the analysis of the dynamical system of our Universe from two dimensional to three dimensional. In addition to the critical points found in previous papers, we find a new de Sitter– like dominant attractor ($cp6$) and give its stable condition using the center manifold theorem. For the dark energy dominant solution ($cp6$ and $cp7$), it could be distinguished from canonical quintessence and tachyon models since the sound speed $c_s^2=0$ or $c_s^2\ll 1$. For the scaling solution ($cp8$), it is very interesting that the sound speed $c_s^2=1/5$, while it behaves as ordinary matter. We therefore point out that the power-law kinetic quintessence should have different signatures on the cold dark matter power spectrum and the cosmic microwave background both at early time, when this scalar field is an early dark energy with ${\mathrm{\Omega }}_{\varphi }$ being non-negligible at high redshift, and at late time, when it drives the accelerating expansion. We still do not know whether there are any degeneracies of the impacts between these two epoches. They are expected to be investigated in future.

In this paper, we focus on general features of quintessential inflation, which is an effort to unify inflation and dark energy using a single scalar field. We describe a class of models of quintessential inflation which can give rise to the tensor to scalar ratio of perturbations consistent with recent BICEP2 measurements. The scale of inflation in the model is around the grand unified theory scale and there is large parameter space consistent with the recent findings.

Various classes of exotic singularity models have been studied as possible mimic models for the observed recent acceleration of the Universe. Here we further study one of these classes and, under the assumption that they are phenomenological toy models for the behavior of an underlying scalar field that also couples to the electromagnetic sector of the theory, obtain the corresponding behavior of the fine-structure constant $\alpha$ for particular choices of model parameters that have been previously shown to be in reasonable agreement with cosmological observations. We then compare this predicted behavior with available measurements of $\alpha$, thus constraining this putative coupling to electromagnetism. We find that values of the coupling that would provide a good fit to spectroscopic measurements of $\alpha$ are in more than three-sigma tension with local atomic clock bounds. Future measurements by ESPRESSO and ELT-HIRES will provide a definitive test of these models.

In the context of Grand Unified Theories (GUT) baryogenesis models, a well-known theorem asserts that $CPT$ conservation and the unitarity of the S matrix require that the lowest order contribution that leads to the generation of a nonzero net $CP$ violation via the decay of a heavy particle must be to $\mathcal{O}({\alpha }_{\cancel{B}}^3)$, where ${\alpha }_{\cancel{B}}$ is a baryon number (B) violating coupling. We revisit this theorem [which holds for lepton number (L) violation, and hence for leptogenesis as well] and examine its implications for models where the particle content allows the heavy particle to also decay via modes which conserve B (or L) in addition to modes which do not. We systematically expand the S matrix order by order in B/L violating couplings, and show, in such cases, that the net $CP$ violation is nonzero even to $\mathcal{O}({\alpha }_{\cancel{B}}^2)$, without actually contradicting the theorem. By replacing a B/L violating coupling (usually constrained to be small) by a relatively unconstrained B/L conserving one, our result may allow for sufficient $CP$ violation in models where it may otherwise have been difficult to generate the observed baryon asymmetry. As an explicit application of this result, we construct a model in low-scale leptogenesis.

We discuss a class of technically natural UV extensions of the Standard Model in which the electroweak scale is shielded from large radiative corrections from heavy UV physics due to an enhanced Poincaré symmetry. Such heavy sectors can be invoked to provide solutions to known shortcomings of the Standard Model, such as the strong-$CP$ problem, the absence of dark matter, and the lack of neutrino masses. We discuss the relationship to scale-invariant models.

Inspired by the recent LHCb measurements and forthcoming great potential on $B_c$ meson, we study the exclusive $B_c\to B_{q}P$, $B_{q}V$ decays with the perturbative QCD approach, where $q=u$, $d$, $s$ and $P$ and $V$ denote the lightest pseudoscalar and vector $SU(3)$ nonet meson, respectively. By retaining the quark transverse momentum, employing the Sudakov factors, and choosing the typical scale as the maximum virtualities of the internal particles, we calculate the $B_c\to B$ transition from factors, and our results show that about 90% of the contribution to form factors comes from the ${\alpha }_s/\pi <0.3$ region. The contributions of penguin and annihilation to branching ratios are very small due to the serious suppression by the CKM factors. There are some hierarchy relations among the $B_c\to BP$, $BV$ decays. The branching ratios for $B_c\to B_{d,s}\pi$, $B_{d,s}\rho$, $B_{s}K$ are large and could be measured by the running LHCb.

By using a $2.92{\mathrm{fb}}^{-1}$ data sample taken at $\sqrt{s}=3.773\mathrm{GeV}$ with the BESIII detector operating at the BEPCII collider, we search for the radiative transitions $\psi (3770)\to \gamma {\eta }_c$ and $\gamma {\eta }_c(2S)$ through the hadronic decays ${\eta }_c({\eta }_c(2S))\to K_S^0{K}^{\pm }{\pi }^{\mp }$. No significant excess of signal events above background is observed. We set upper limits at a 90% confidence level for the product branching fractions to be $\mathcal{B}(\psi (3770)\to \gamma {\eta }_c)\times \mathcal{B}({\eta }_c\to K_S^0{K}^{\pm }{\pi }^{\mp })<1.6\times {10}^{-5}$ and $\mathcal{B}(\psi (3770)\to \gamma {\eta }_c(2S))\times \mathcal{B}({\eta }_c(2S)\to K_S^0{K}^{\pm }{\pi }^{\mp })<5.6\times {10}^{-6}$. Combining our result with world-average values of $\mathcal{B}({\eta }_c({\eta }_c(2S))\to K_S^0{K}^{\pm }{\pi }^{\mp })$, we find the branching fractions $\mathcal{B}(\psi (3770)\to \gamma {\eta }_c)<6.8\times {10}^{-4}$ and $\mathcal{B}(\psi (3770)\to \gamma {\eta }_c(2S))<2.0\times {10}^{-3}$ at a 90% confidence level.

We present the first observation of a flavor-singlet scalar meson as light as the pion in $N_f=8$ QCD on the lattice, using the highly improved staggered quark action. Such a light scalar meson can be regarded as a composite Higgs with mass 125 GeV. In accord with our previous lattice results showing that the theory exhibits walking behavior, the light scalar may be a technidilaton, a pseudo-Nambu-Goldstone boson of the approximate scale symmetry in walking technicolor.

It has been argued in the literature that in order to make a matter dominated Friedmann–Lemaitre–Robertson–Walker universe compatible with the generalized second law of thermodynamics one must invoke dark energy or modified gravity. In the present article, we investigate if, in a similar spirit, inhomogeneous cosmological models can be motivated on thermodynamic grounds. We examine a particular minimal void Lemaitre–Tolman–Bondi inhomogeneous model that agrees well with observations. While on the one hand we find that the entropy associated with the apparent horizon is not well behaved thermodynamically, on the other hand, the canonical Weyl curvature entropy shows satisfactory thermodynamic behavior. We suggest that evolution of canonical Weyl curvature entropy might be a useful way to evaluate the thermodynamic viability of inhomogeneous cosmologies.

We study the photoproduction of isolated prompt photons associated with hadron jets in the framework of the parton Reggeization approach. The cross section distributions in the transverse energies and pseudorapidities of the prompt photon and the jet as well as the azimuthal-decorrelation variables measured by the H1 and ZEUS collaborations at DESY HERA are nicely described by our predictions. The main improvements with respect to previous studies in the $k_T$-factorization framework include the application of the Reggeized-quark formalism, the generation of exactly gauge-invariant amplitudes with off-shell initial-state quarks, and the exact treatment of the $\gamma R\to \gamma g$ box contribution with off-shell initial-state gluons.

We find that the four-dimensional cosmological Einstein-Yang-Mills theory with $SU(2)$ gauge group admits Lifshitz spacetime as a base solution for the dynamical exponent $z>1$. Motivated by this, we next demonstrate numerically that the field equations admit black hole solutions which behave regularly on the horizon and at spatial infinity for different horizon topologies. The solutions depend on one parameter, the strength of the gauge field at the horizon, which is fine-tuned to capture the Lifshitz asymptotics at infinity. We also discuss the behavior of solutions and the change in Hawking temperature for black holes that are large or small with respect to the length scale $L$, which is itself fixed by the value of the cosmological constant.

It is commonly accepted that general relativity is the only solution to the consistency problem that appears when trying to build a theory of interacting gravitons (massless spin-2 particles). Padmanabhan’s 2008 thought-provoking analysis raised some concerns that are having resonance in the community. In this paper we present the self-coupling problem in detail and explicitly solve the infinite-iterations scheme associated with it for the simplest theory of a graviton field, which corresponds to an irreducible spin-2 representation of the Poincaré group. We make explicit the nonuniqueness problem by finding an entire family of solutions to the self-coupling problem. Then we show that the only resulting theory which implements a deformation of the original gauge symmetry happens to have essentially the structure of unimodular gravity. This makes plausible the possibility of a natural solution to the first cosmological constant problem in theories of emergent gravity. Later on, we change for the sake of completeness the starting free-field theory to Fierz-Pauli theory, an equivalent theory but with a larger gauge symmetry. We indicate how to carry out the infinite summation procedure in a similar way. Overall, we conclude that as long as one requires the (deformed) preservation of internal gauge invariance, one naturally recovers the structure of unimodular gravity or general relativity but in a version that explicitly shows the underlying Minkowski spacetime, in the spirit of Rosen’s flat-background bimetric theory.

We consider Lagrangians in $3+1$ dimensions admitting topological defects where there is an additional coupling between the defect scalar field $\mathrm{\Phi }$ and the gauge field kinetic term (e.g. $B(|\mathrm{\Phi }{|}^2)F_{\mu \nu }{F}^{\mu \nu }$). Such a dilatonic coupling in the context of a static defect induces a spatially dependent effective gauge charge and effective mass for the scalar field, which leads to modified properties of the defect core. In particular, the scale of the core gets modified while the stability properties of the corresponding embedded defects are also affected. These modifications are illustrated for gauged (Nielsen-Olesen) vortices and for gauged (’t Hooft–Polyakov) monopoles. The corresponding dilatonic global defects are also studied in the presence of an external gauge field.