We argue that classical spacetimes represent amplified information in the holographic theory of quantum gravity. In general, classicalization of a quantum system involves amplification of information at the cost of exponentially reducing the number of observables. In quantum gravity, the geometry of spacetime must be the analogously amplified information. Bulk local semiclassical operators probe this information without disturbing it; these correspond to logical operators acting on code subspaces of the holographic theory. From this viewpoint, we study how bulk local operators may be realized in a holographic theory of general spacetimes, which includes $\mathrm{AdS}/\mathrm{CFT}$ as a special case, and deduce its consequences. In the first half of the paper, we ask what description of the bulk physics is provided by a holographic state dual to a semiclassical spacetime. In particular, we analyze what portion of the bulk can be reconstructed as spacetime in the holographic theory. The analysis indicates that when a spacetime contains a quasistatic black hole inside a holographic screen, the theory provides a description of physics as viewed from the exterior (though the interior information is not absent). In the second half, we study how and when a semiclassical description emerges in the holographic theory. We find that states representing semiclassical spacetimes are non-generic in the holographic Hilbert space. If there are a maximal number of independent microstates, semiclassical operators must be given state-dependently; we elucidate this point using the stabilizer formalism and tensor network models. We also discuss possible implications of the present picture for the black hole interior.

We study the $O(N_1)\times O(N_2)\times O(N_3)$ symmetric quantum mechanics of 3-index Majorana fermions. When the ranks $N_i$ are all equal, this model has a large $N$ limit which is dominated by the melonic Feynman diagrams. We derive an integral formula which computes the number of group invariant states for any set of $N_i$. It is non-vanishing only when each $N_i$ is even. For equal ranks the number of singlets exhibits rapid growth with $N$: it jumps from 36 in the $O(4{)}^3$ model to 595 354 780 in the $O(6{)}^3$ model. We derive bounds on the values of energy, which show that they scale at most as $N^3$ in the large $N$ limit, in agreement with expectations. We also show that the splitting between the lowest singlet and non-singlet states is of order $1/N$. For $N_3=1$ the tensor model reduces to $O(N_1)\times O(N_2)$ fermionic matrix quantum mechanics, and we find a simple expression for the Hamiltonian in terms of the quadratic Casimir operators of the symmetry group. A similar expression is derived for the complex matrix model with $SU(N_1)\times SU(N_2)\times U(1)$ symmetry. Finally, we study the $N_3=2$ case of the tensor model, which gives a more intricate complex matrix model whose symmetry is only $O(N_1)\times O(N_2)\times U(1)$. All energies are again integers in appropriate units, and we derive a concise formula for the spectrum. The fermionic matrix models we studied possess standard ’t Hooft large $N$ limits where the ground state energies are of order $N^2$, while the energy gaps are of order 1.

We relate the notion of unitarity of a ($0+1$)-D conformally ($SL(2,\mathbf{R})$) invariant field theory with that of a nonrelativistic conformal (Schrödinger) field theory using the fact that $SL(2,\mathbf{R})$ is a subgroup of nonrelativistic conformal (Schrödinger) group. Exploiting $SL(2,\mathbf{R})$ unitarity, we derive the unitarity bounds and null conditions for a Schrödinger field theory (for the neutral as well as the charged sector). In noninteger dimensions the theory is shown to be nonunitary. The use of the $SL(2,\mathbf{R})$ subgroup opens up the possibility of borrowing results from ($0+1$)-D $SL(2,\mathbf{R})$ invariant field theory to explore Schrödinger field theory, in particular, the neutral sector, which has otherwise been unexplored.

We investigate the radiative processes of a quantum system composed by two identical two-level atoms in the de Sitter spacetime, interacting with a conformally coupled massless scalar field prepared in the de Sitter-invariant vacuum. We discuss the structure of the rate of variations of the atomic energy for two static atoms. Following a procedure developed by Dalibard, Dupont-Roc, and Cohen-Tannoudji, our intention is to identify in a quantitative way the contributions of vacuum fluctuations and the radiation reaction to the generation of quantum entanglement and to the degradation of entangled states. We find that when the distance between two atoms larger than the characteristic length scale, the rate of variation of atomic energy in the de Sitter-invariant vacuum behaves differently compared with that in the thermal Minkowski spacetime. In particular, the generation and degradation of quantum entanglement can be enhanced or inhibited, which are dependent not only on the specific entangled state but also on the distance between the atoms.

We establish the multiplicative renormalization procedure of generalized scalar Duffin-Kemmer-Petiau electrodynamics (${\mathrm{GSDKP}}_4$) in the mass shell. We show an explicit calculation of the first radiative corrections (one-loop) associated with the photon propagator, meson propagator, vertex function, and photon-photon four-point function utilizing the dimensional regularization method, where the gauge symmetry is manifest. As we will see, one of the consequences of the study is that, from the complete photon propagator renormalization condition, imposing that it behaves as a massless field, an energy range where ${\mathrm{GSDKP}}_4$ is well defined is $m^2\ll k^2<m_p^2$, by evaluating the effective coupling constant. From the complete DKP propagator, we will present two ways of evaluating the renormalizaton conditions for the pole and residue, due to DKP trilinear algebra. We will also see that the DKP algebra ensures that the Ward-Fradkin-Takahashi (WFT) identities in the first radiative corrections of the vertex and photon-photon four-point function prohibit UV divergences. Furthermore, in order to show the effectiveness of the renormalization procedure on the present theory, a diagrammatic discussion of the photon self-energy and vertex part at ${\alpha }^2$ order is presented.

It is believed that in any number of dimensions the off-shell Kerr–NUT–(A)dS metric represents a unique geometry admitting the principal (rank 2, non-degenerate, closed conformal Killing–Yano) tensor. The original proof relied on the Euclidean signature and therein natural assumption that the eigenvalues of the principal tensor have gradients of spacelike character. In this paper we evade this common wisdom and construct new classes of Lorentzian (and other signature) off-shell metrics admitting the principal tensor with “null eigenvalues,” uncovering so a much richer structure of spacetimes with principal tensor in four and higher dimensions. A few observations regarding the Kerr–Schild ansatz are also made.

We review the equation of state (EoS) approach to dark sector perturbations and apply it to $f(\mathcal{R})$ gravity models of dark energy. We show that the EoS approach is numerically stable and use it to set observational constraints on designer models. Within the EoS approach we build an analytical understanding of the dynamics of cosmological perturbations for the designer class of $f(\mathcal{R})$ gravity models, characterized by the parameter $B_0$ and the background equation of state of dark energy $w$. When we use the Planck cosmic microwave background temperature anisotropy, polarization, and lensing data as well as the baryonic acoustic oscillation data from SDSS and WiggleZ, we find $B_0<0.006$ (95% C.L.) for the designer models with $w=-1$. Furthermore, we find $B_0<0.0045$ and $|w+1|<0.002$ (95% C.L.) for the designer models with $w\ne -1$. Previous analyses found similar results for designer and Hu-Sawicki $f(\mathcal{R})$ gravity models using the effective field theory approach [Raveri et al., Phys. Rev. D 90, 043513 (2014); Hu et al., Mon. Not. R. Astron. Soc. 459, 3880 (2016)]; therefore this hints for the fact that generic $f(\mathcal{R})$ models with $w\ne -1$ can be tightly constrained by current cosmological data, complementary to solar system tests [Brax et al., Phys. Rev. D 78, 104021 (2008); Faulkner et al., Phys. Rev. D 76, 063505 (2007)]. When compared to a $w\mathrm{CDM}$ fluid with the same sound speed, we find that the equation of state for $f(\mathcal{R})$ models is better constrained to be close to $-1$ by about an order of magnitude, due to the strong dependence of the perturbations on $w$.

We derive a generalized deviation equation in Riemann-Cartan spacetime. The equation describes the dynamics of the connecting vector, which links events on two general adjacent world lines. Our result is valid for any theory in a Riemann-Cartan background; in particular, it is applicable to a large class of gravitational theories that go beyond the general relativistic framework.

Alternative theories of gravity may serve to overcome several shortcomings of the standard cosmological model but, in their weak field limit, general relativity must be recovered so as to match the tight constraints at the Solar System scale. Therefore, testing such alternative models at scales of stellar systems could give a unique opportunity to confirm or rule them out. One of the most straightforward modifications is represented by analytical $f(R)$-gravity models that introduce a Yukawa-like modification to the Newtonian potential thus modifying the dynamics of particles. Using the geodesics equations, we have illustrated the amplitude of these modifications. First, we have integrated numerically the equations of motion showing the orbital precession of a particle around a massive object. Second, we have computed an analytic expression for the periastron advance of systems having their semimajor axis much shorter than the Yukawa-scale length. Finally, we have extended our results to the case of a binary system composed of two massive objects. Our analysis provides a powerful tool to obtain constraints on the underlying theory of gravity using current and forthcoming data sets.

The concordance cosmological model has been successfully tested over the last decades. Despite its successes, the fundamental nature of dark matter and dark energy is still unknown. Modifications of the gravitational action have been proposed as an alternative to these dark components. The straightforward modification of gravity is to generalize the action to a function, $f(R)$, of the scalar curvature. Thus one is able to describe the emergence and the evolution of the large scale structure without any additional (unknown) dark component. In the weak field limit of the $f(R)$-gravity, a modified Newtonian gravitational potential arises. This gravitational potential accounts for an extra force, generally called fifth force, that produces a precession of the orbital motion even in the classic mechanical approach. We have shown that the orbits in the modified potential can be written as Keplerian orbits under some conditions on the strength and scale length of this extra force. Nevertheless, we have also shown that this extra term gives rise to the precession of the orbit. Thus, comparing our prediction with the measurements of the precession of some planetary motions, we have found that the strength of the fifth force must be in the range $[2.70–6.70]\times {10}^{-9}$ with the characteristic scale length to fix to the fiducial values of $\sim 5000\mathrm{AU}$.

In modified gravity the propagation of gravitational waves (GWs) is in general different from that in general relativity. As a result, the luminosity distance for GWs can differ from that for electromagnetic signals, and is affected both by the dark energy equation of state $w_{\mathrm{DE}}(z)$ and by a function $\delta (z)$ describing modified propagation. We show that the effect of modified propagation in general dominates over the effect of the dark energy equation of state, making it easier to distinguish a modified gravity model from $\mathrm{\Lambda }\mathrm{CDM}$. We illustrate this using a nonlocal modification of gravity that has been shown to fit remarkably well cosmic microwave background, supernovae, baryon acoustic oscillation, and structure formation data, and we discuss the prospects for distinguishing nonlocal gravity from $\mathrm{\Lambda }\mathrm{CDM}$ with the Einstein Telescope. We find that, depending on the exact sensitivity, a few tens of standard sirens with measured redshift at $z\sim 0.4$, or a few hundreds at $1\lesssim z\lesssim 2$, could suffice.

We develop a self-consistent, gravitoelectromagnetic (GEM) formulation of a slowly rotating, self-gravitating, and dilute Bose-Einstein condensate (BEC), intended for astrophysical applications in the context of dark matter halos. GEM self-consistently incorporates the effects of frame dragging to lowest order in $v/c$ via the gravitomagnetic field. BEC dark matter has attracted attention as an alternative to cold dark matter and warm dark matter for some time now. The BEC is described by the Gross-Pitaevskii-Poisson equation with an arbitrary potential allowing for either attractive or repulsive interactions. Owing to the difficulty in obtaining exact solutions to the GEM equations of motion without drastic approximations, we employ the variational method to examine the conditions under which rotating condensates, stable against gravitational collapse, may form in models with attractive and repulsive quartic interactions. We also describe the approximate dynamics of an imploding and rotating condensate by employing a collective coordinate description in terms of the condensate radius.

Indirect detection of dark matter (DM) by multiwavelength astronomical observations provides a promising avenue for probing the particle nature of DM. In the case of DM consisting of weakly interacting massive particles (WIMPs), self-annihilation ultimately produces various observable products including $e^{\pm }$ pairs and gamma rays. The gamma rays can be detected directly, while the $e^{\pm }$ pairs can be detected by radio emission from synchrotron radiation or X rays and soft gamma rays from inverse Compton scattering. An intriguing region to search for astrophysical signs of DM is the Galactic center (GC) of the Milky Way, due in part to an observed excess of gamma rays that could be DM. A recent observation by the Fermi-LAT collaboration of a similar excess in the central region of the Andromeda galaxy (M31) leads us to explore the possibility of a DM-induced signal there as well. We use the RX-DMFIT tool to perform a multifrequency analysis of potential DM annihilation emissions in M31. We consider WIMP particle models consistent with the GC excess and calculate the expected emission across the electromagnetic spectrum in comparison with available observational data from M31. We find that the particle models that best fit the M31 excess favor lower masses than the GC excess. The best-fitting models are for a $b\overline{b}$ final state with $M_{\chi }=11\mathrm{GeV}$ and $⟨\sigma v⟩=2.6\times {10}^{-26}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$, as well as an evenly mixed $b\overline{b}/{\tau }^{+}{\tau }^{-}$ final state with $M_{\chi }=5.8\mathrm{GeV}$ and $⟨\sigma v⟩=2.03\times {10}^{-26}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$. For conservative estimates of the diffusion and magnetic field models the expected radio emissions appear to be in tension with currently available data in the central region of M31, although this constraint has a fairly strong dependence on the values chosen for parameters describing the magnetic field strength and geometry.

The LUX experiment has performed searches for dark-matter particles scattering elastically on xenon nuclei, leading to stringent upper limits on the nuclear scattering cross sections for dark matter. Here, for results derived from $1.4\times {10}^4\mathrm{kg}$ days of target exposure in 2013, details of the calibration, event-reconstruction, modeling, and statistical tests that underlie the results are presented. Detector performance is characterized, including measured efficiencies, stability of response, position resolution, and discrimination between electron- and nuclear-recoil populations. Models are developed for the drift field, optical properties, background populations, the electron- and nuclear-recoil responses, and the absolute rate of low-energy background events. Innovations in the analysis include in situ measurement of the photomultipliers’ response to xenon scintillation photons, verification of fiducial mass with a low-energy internal calibration source, and new empirical models for low-energy signal yield based on large-sample, in situ calibrations.

Correlated magnetic noise from Schumann resonances threatens to contaminate the observation of a stochastic gravitational-wave background in interferometric detectors. In previous work, we reported on the first effort to eliminate global correlated noise from the Schumann resonances using Wiener filtering, demonstrating as much as a factor of two reduction in the coherence between magnetometers on different continents. In this work, we present results from dedicated magnetometer measurements at the Virgo and KAGRA sites, which are the first results for subtraction using data from gravitational-wave detector sites. We compare these measurements to a growing network of permanent magnetometer stations, including at the LIGO sites. We show the effect of mutual magnetometer attraction, arguing that magnetometers should be placed at least one meter from one another. In addition, for the first time, we show how dedicated measurements by magnetometers near to the interferometers can reduce coherence to a level consistent with uncorrelated noise, making a potential detection of a stochastic gravitational-wave background possible.

We study the second derivative effects on the constitutive relations of an uncharged parity-even Galilean fluid using the null fluid framework. Null fluids are an equivalent representation of Galilean fluids in terms of a higher dimensional relativistic fluid, which makes the Galilean symmetries manifest and tractable. The analysis is based on the off-shell formalism of hydrodynamics. We use this formalism to work out a generic algorithm to obtain the constitutive relations of a Galilean fluid up to arbitrarily high derivative orders, and later specialize to second order. Finally, we study the Stokes’ law which determines the drag force on an object moving through a fluid, in presence of certain second order terms. We identify the second order transport coefficients which leave the drag force invariant.

Factorization violating effects in hadron scattering are due mainly to spectator-spectator interactions. While it is known that these interactions cancel in inclusive cross sections, as for the Drell-Yan process, not much is known about for what classes of observables factorization is violated. We show that for pure Glauber ladder graphs, all amplitude-level factorization violating effects completely cancel at the cross section level for any single-scale observable (such as hadronic transverse energy or beam thrust). This result disproves previous claims that these pure Glauber graphs are factorization violating. Our proof exploits scale invariance of two-to-two scattering amplitudes in an essential way. The leading factorization violating effects therefore come from graphs with at least one soft gluon, involving the Lipatov vertex off of the Glauber ladders. This implies that real soft radiation must be involved in factorization violation, shedding light on the connection between factorization violation and the underlying event.

The Salpeter contribution to the Lamb shift in a hydrogenlike atom with a pointlike spin-$1/2$ nucleus was considered long time ago and the result, exact in $m/M$, has been obtained. In this paper we consider the case of the nuclear spin 1.

Deviation from the standard model prediction is observed in many semileptonic $B$ decays mediated via $b\to c$ charged current interactions. In particular, current experimental measurements of the ratio of branching ratio $R_D$ and $R_{D^{*}}$ in $B\to D^{(*)}l\nu$ decays disagree with standard model expectations at the level of about $4.1\sigma$. Moreover, the recent measurement of the ratio of branching ratio $R_{J/\mathrm{\Psi }}$ by LHCb, where $R_{J/\mathrm{\Psi }}=\mathcal{B}(B_c\to J/\mathrm{\Psi }\tau \nu )/\mathcal{B}(B_c\to J/\mathrm{\Psi }\mu \nu )$, is more than $2\sigma$ away from the standard model prediction. In this context, we consider an effective Lagrangian in the presence of vector and scalar new physics couplings to study the implications of $R_D$ and $R_{D^{*}}$ anomalies in $B_s\to D_s\tau \nu$ decays. We give a prediction of several observables such as the branching ratio, ratio of branching ratio, forward backward asymmetry parameter, $\tau$ polarization fraction, and convexity parameter for the $B_s\to D_s\tau \nu$ decays within the standard model and within various new physics scenarios.