We investigate a quantum vacuum state for ($1+1$)-dimensional de Sitter space, corresponding to a region within a perfectly reflecting symmetric box of fixed physical size. We find that a particle detector inside the box registers zero response, implying that the walls of the box screen out the thermal effects of the de Sitter horizon. The box thus creates a “quiescent oasis” with a temperature below the de Sitter horizon temperature, an unexpected feature that opens the way to an analysis of heat and entropy exchange between the box and the horizon in the context of the generalized second law of thermodynamics. We also calculate the stress-energy-momentum tensor of the region within the box, showing that the total energy in the box is less than the same volume of de Sitter space in the presence of thermal fluctuations.

In a recent report, Carballo-Rubio [R. Carballo-Rubio, Stellar Equilibrium in Semiclassical Gravity, Phys. Rev. Lett. 120, 061102 (2018)] utilizes the semi-classical theory of gravity to obtain a generalized Tolman-Oppenheimer-Volkoff (TOV) equation. This model has a new coupling constant $l_p$ implying two different modified TOV equation forms characterized by the sign of $p^{\prime }$. The negative branch reduces to the ordinary GR-TOV in the limit of $l_p\to 0$, while the positive one does not. In the positive branch, Carballo-Rubio was able to find the exact solutions using the constant-$\lambda$ trick. In this work, we investigate whether this theory’s negative branch can also provide a different feature of the ultra-compact object compared to those obtained from the GR-TOV equation. We use a numerical method to calculate the properties of an ultra-compact object. We tested our code by calculating numerically the pressure profile of the object in a positive branch with the star’s radius $R$ in a macroscopic unit by integrating from surface to center. The result reproduces the analytical result of Carballo-Rubio [R. Carballo-Rubio, Stellar Equilibrium in Semiclassical Gravity, Phys. Rev. Lett. 120, 061102 (2018)]. While in a negative branch, we reproduce the pressure profile results of Ho and Matsuo [P. M. Ho and Y. Matsuo, Static black hole and vacuum energy: Thin shell and incompressible fluid, J. High Energy Phys. 03 (2018) 096] using constant energy density $\rho ={\rho }_0$ not only by integrating from surface to center but also by integrating from center to surface, respectively. In this work, we study ultra-compact objects with an isotropically ideal fluid matter where we use a simple but physically motivated equation of state $\rho =p/w+{\rho }_0$ with $w=1$ and $w=1/3$. In general, we obtain that the range of $l_p$ is very restricted and must not be equal to $r_c$. Here $r_c$ is the starting point of integration located at the center of the star. While $l_p$ should be set to be much larger than Planck length $L_{\mathrm{Pl}}$. Consequently, the mass-radius curves for the various value of $l_p$ for both $w$ cases are still indistinguishable from the standard GR-TOV results. Hence from the negative branch of $p^{\prime }(r)$, the additional free parameter $l_p$ does not provide a significant effect compared to the standard GR-TOV equation results, even though $l_p$ is not in the limit of $l_p\to 0$ anymore. Therefore, similar to the conclusion in [A. Urbano and H. Veerme, On gravitational echoes from ultracompact exotic stars, J. Cosmol. Astropart. Phys. 04 (2019) 011] with GR theory that the ultra-compact objects from negative branch of semi-classical gravity with a linear equation of state are unable to generate demanding gravitational echoes.

An exponential kind of quintessential inflation potential motivated by supergravity is studied. This type belongs to the class of $\alpha$-attractor models. The model was studied for the first time by Dimopoulos and Owen in [J. Cosmol. Astropart. Phys. 06 (2017) 027], in which the authors introduced a negative cosmological constant in order to ensure a zero-vacuum energy density at late times. However, in this paper, we disregard this cosmological constant, showing that the obtained results are very close to the ones obtained recently in the context of Lorentzian quintessential inflation and thus depicting with great accuracy the early- and late-time acceleration of our Universe. The model is compatible with the recent observations. Finally, we review the treatment of the $\alpha$-attractor and we show that our potential depicts the late time cosmic acceleration with an effective equation of state equal to $-1$.

The Alcock-Paczynski (AP) effect is a geometrical distortion in three-dimensional observed galaxy statistics. In anticipation of precision cosmology based on ongoing and upcoming all-sky galaxy surveys, we build an efficient method to compute the AP-distorted correlations of galaxy number density and peculiar velocity fields for any larger angular scale not relying on the conventionally used plane-parallel (PP) approximation. Here, instead of the usual Legendre polynomial basis, the correlation functions are decomposed using tripolar spherical harmonic basis; hence, characteristic angular dependence due to the wide-angle AP effect can be rigorously captured. By means of this, we demonstrate the computation of the AP-distorted correlations over the various scales. Comparing our results with the PP-limit ones, we confirm that the errors due to the PP approximation become more remarkable as the visual angle of separation between target galaxies, $\mathrm{\Theta }$, enlarges, and especially for the density auto correlation, the error exceeds 10% when $\mathrm{\Theta }\gtrsim 30°$. This highlights the importance of the analysis beyond the PP approximation.

We study a gravitating spherically symmetric nonrelativistic configuration consisting of a spinor fluid whose effective equation of state is derived from a consideration of a limiting system supported by a massive nonlinear spinor field. For such a configuration, we find a two-parametric family of static regular solutions describing compact objects whose masses and sizes are determined by the central density of the spinor fluid and the mass of the spinor field. Using the similarity method, we consider a gravitational collapse of an initially uniform system consisting of the spinor fluid. We estimate the general characteristics of the collapse and show that a resulting nonuniform distribution of the fluid occurs that may serve as a core for the creation of equilibrium starlike configurations.

Measuring the solar neutrino flux over gigayear timescales could provide a new window to inform the solar standard model as well as studies of the Earth’s long-term climate. We demonstrate the feasibility of measuring the time evolution of the ${}^8\mathrm{B}$ solar neutrino flux over gigayear timescales using paleo detectors, naturally occurring minerals which record neutrino-induced recoil tracks over geological times. We explore suitable minerals and identify track lengths of 15–30 nm to be a practical window to detect the ${}^8\mathrm{B}$ solar neutrino flux. A collection of ultraradiopure minerals of different ages, each some 0.1 kg by mass, can be used to probe the rise of the ${}^8\mathrm{B}$ solar neutrino flux over the recent gigayear of the Sun’s evolution. We also show that the time-integrated tracks are sensitive to models of the Sun.

Gravitational waves enable tests of general relativity in the highly dynamical and strong-field regime. Using events detected by LIGO-Virgo up to 1 October 2019, we evaluate the consistency of the data with predictions from the theory. We first establish that residuals from the best-fit waveform are consistent with detector noise, and that the low- and high-frequency parts of the signals are in agreement. We then consider parametrized modifications to the waveform by varying post-Newtonian and phenomenological coefficients, improving past constraints by factors of $\sim 2$; we also find consistency with Kerr black holes when we specifically target signatures of the spin-induced quadrupole moment. Looking for gravitational-wave dispersion, we tighten constraints on Lorentz-violating coefficients by a factor of $\sim 2.6$ and bound the mass of the graviton to $m_g\le 1.76\times {10}^{-23}\mathrm{eV}/c^2$ with 90% credibility. We also analyze the properties of the merger remnants by measuring ringdown frequencies and damping times, constraining fractional deviations away from the Kerr frequency to $\delta {\widehat{f}}_{220}=0.03_{-0.35}^{+0.38}$ for the fundamental quadrupolar mode, and $\delta {\widehat{f}}_{221}=0.04_{-0.32}^{+0.27}$ for the first overtone; additionally, we find no evidence for postmerger echoes. Finally, we determine that our data are consistent with tensorial polarizations through a template-independent method. When possible, we assess the validity of general relativity based on collections of events analyzed jointly. We find no evidence for new physics beyond general relativity, for black hole mimickers, or for any unaccounted systematics.

Axion as one of the promising dark matter candidates can be detected through narrow radio lines emitted from the magnetic white dwarf stars. Due to the existence of the strong magnetic field, the axion may resonantly convert into the radio photon (Primakoff effect) when it passes through a narrow region in the corona of the magnetic white dwarf, where the plasma frequency is equal to the axion mass. We show that for the magnetic white dwarf WD $2010+310$, the future experiment SKA phase 1 with 100 hours of observation can effectively probe the parameter space of the axion-photon coupling $g_{a\gamma }$ up to $\sim {10}^{-12}{\mathrm{GeV}}^{-1}$ for the axion mass range of $0.2\sim 3.7\mu \mathrm{eV}$. Note that in the low mass region ($m_a\lesssim 1.5\mu \mathrm{eV}$), the WD $2010+310$ could give greater sensitivity than the neutron star RX J0806.4-4123.

We investigate the prospects of discovering the top-quark decay into a charm quark and a Higgs boson ($t\to c{h}^0$) in top-quark pair production at the CERN Large Hadron Collider (LHC). A general two-Higgs-doublet model is adopted to study flavor-changing neutral Higgs (FCNH) interactions. We perform a parton-level analysis as well as Monte Carlo simulations using Pythia 8 and Delphes to study the flavor-changing top-quark decay $t\to c{h}^0$, followed by the Higgs decaying into ${\tau }^{+}{\tau }^{-}$, with the other top quark decaying to a bottom quark ($b$) and two light jets ($t\to bW\to bjj$). To reduce the physics background to the Higgs signal, only the leptonic decays of tau leptons are considered, ${\tau }^{+}{\tau }^{-}\to e^{\pm }{\mu }^{\mp }+{\cancel{E}}_T$, where ${\cancel{E}}_T$ represents the missing transverse energy from the neutrinos. In order to reconstruct the Higgs boson and top-quark masses as well as to reduce the physics background, the collinear approximation for the highly boosted tau decays is employed. Furthermore, the energy distribution of the charm quark helps set the acceptance criteria used to reduce the background and improve the statistical significance of the signal. We study the discovery potential for the FCNH top decay at the LHC with collider energy $\sqrt{s}=13$ and 14 TeV as well as a future hadron collider with $\sqrt{s}=27\mathrm{TeV}$. Our analysis suggests that a high-energy LHC at $\sqrt{s}=27\mathrm{TeV}$ will be able to discover this FCNH signal with an integrated luminosity $\mathcal{L}=3{\mathrm{ab}}^{-1}$ for a branching fraction $\mathcal{B}(t\to c{h}^0)\gtrsim 1.4\times {10}^{-4}$, which corresponds to a FCNH coupling $|{\lambda }_{tch}|\gtrsim 0.023$. This FCNH coupling is significantly below the current ATLAS combined upper limit of $|{\lambda }_{tch}|=0.064$.

After inflation the Universe presumably undergoes a phase of reheating which in effect starts the thermal big bang cosmology. However, so far we have very little direct experimental or observational evidence of this important phase of the Universe. In this paper, we argue that measuring the spectrum of freely propagating relativistic particles, i.e., dark radiation, produced during reheating may provide us with powerful information on the reheating phase. To demonstrate this possibility we consider a situation where the dark radiation is produced in the decays of heavy, nonrelativistic particles. We show that the spectrum crucially depends on whether the heavy particle once dominated the Universe or not. Characteristic features caused by the dependence on the number of the relativistic degrees of freedom may even allow to infer the temperature when the decay of the heavy particle occurred.

We use the nCTEQ analysis framework to investigate nuclear parton distribution functions (nPDFs) in the region of large $x$ and intermediate-to-low $Q$, with special attention to recent JLab deep inelastic scattering data on nuclear targets. This data lies in a region which is often excluded by $W$ and $Q$ cuts in global nPDF analyses. As we relax these cuts, we enter a new kinematic region, which introduces new phenomenology. In particular, we study the impact of (i) target mass corrections, (ii) higher twist corrections, (iii) deuteron corrections, and (iv) the shape of the nuclear PDF parametrization at large-$x$ close to one. Using the above tools, we produce a new nPDF set (named nCTEQ15HIX) which yields a good description of the new JLab data in this challenging kinematic region, and displays reduced uncertainties at large $x$, in particular for up and down quark flavors.

Complex singularities have been suggested in propagators of confined particles, e.g., the Landau-gauge gluon propagator. We rigorously reconstruct Minkowski propagators from Euclidean propagators with complex singularities. As a result, the analytically continued Wightman function is holomorphic in the tube, and the Lorentz symmetry and locality are kept intact, whereas the reconstructed Wightman function violates the temperedness and the positivity condition. Moreover, we argue that complex singularities correspond to confined zero-norm states in an indefinite metric state space.

Imprints of spinor-vector dualities have been uncovered in various string constructions. They are typically induced by changing certain free general Gliozzi, Scherk, Olive (GSO) phases in the underlying string partition functions. This paper shows that spinor–vector dualities in six dimensions are constrained by a fundamental effective field theory consistency condition, namely that any six-dimensional low energy theory must be free of irreducible $SO(2N)$ anomalies. Aspects of spinor-vector dualities are analyzed in four six-dimensional free fermionic models, which are distinguished by two generalized GSO phases. In addition, the constraint on the number of spinors and vectors is confirmed on generic spectra that may occur in K3 line bundle compactifications of the heterotic $E_8\times E_8$ string.

We discuss nuclear physics in the Witten-Sakai-Sugimoto model, in the limit of large number $N_c$ of colors and large ’t Hooft coupling, with the addition of a finite mass for the quarks. Individual baryons are described by classical solitons whose size is much smaller than the typical distance in nuclear bound states; thus, we can use the linear approximation to compute the interaction potential and provide a natural description for lightly bound states. We find the classical geometry of nuclear bound states for baryon numbers up to $B=8$. The effect of the finite pion mass—induced by the quark mass via the Gell-Mann–Oakes–Renner relation—is to decrease the binding energy of the nuclei with respect to the massless case. We discuss the finite density case with a particular choice of a cubic lattice, for which we find the critical chemical potential, at which the hadronic phase transition occurs.

The paper explores general relativistic (GR) effects in electromagnetic fields of the rotating neutron star. The star has been assumed as a perfect conductor with infinity electric conductivity, i.e., $\sigma \to \infty$. The analytical form of general relativistic Maxwell’s equations for the electromagnetic fields has been derived in the presence of gravity. It is shown that six components of the electromagnetic fields can be expressed in terms of two profile functions. It has been shown that the Lense-Thirring term plays an important role in the generation of the multipole electromagnetic fields. We obtain that the rotation of the quadrupole magnetic field can create the dipole electric field. Moreover, we have also shown that GR effects are reasonably large for the highest order of electromagnetic multipole. Finally, as a test of our results, we investigate the effect of the Lense-Thirring term on the luminosity of magnetodipolar radiations.

We report on the initial results obtained with an image convolution/deconvolution computer code that we developed and used to study the image formation capabilities of the solar gravitational lens (SGL). Although the SGL of a spherical sun creates a greatly blurred image, knowledge of the SGL’s point-spread function makes it possible to reconstruct the original image and remove the blur by way of deconvolution. We discuss the deconvolution process, which can be implemented either with direct matrix inversion or with the Fourier quotient method. We observe that the process introduces a “penalty” in the form of a reduction in the signal-to-noise ratio (SNR) of a recovered image, compared to the SNR at which the blurred image data are collected. We estimate the magnitude of this penalty using an analytical approach and confirm the results with a series of numerical simulations. We find that the penalty is substantially reduced when the spacing between image samples is large compared to the telescope aperture. The penalty can be further reduced with suitable noise filtering, which can yield $\mathcal{O}(10)$ or better improvement for low-quality imaging data. Our results confirm that it is possible to use the SGL for imaging purposes. We offer insights on the data collection and image processing strategies that could yield a detailed image of an exoplanet within image data collection times that are consistent with the duration of a realistic space mission.

We consider the self-collision of portals in classical general relativity. Portals are wormholes supported by a single loop of negative mass cosmic string, and being wormholes, portals have a nontrivial topology. Portals can be constructed so that the curvature is zero everywhere outside the cosmic string, with vanishing ADM mass. The conical singularities of these wormholes can be smoothed, yielding a spatial topology of $S^2\times S^1$ with a point corresponding to spatial infinity removed. If one attempts to collide the mouths of a smoothed portal to induce self-annihilation, one naively might think that a Euclidean topology is recovered, which would violate the classical no topology change theorems. We consider a particular limit of smoothed portals supported by an anisotropic fluid, and find that while the portal mouths do not experience an acceleration as they are brought close together, a curvature singularity forms in the limit that the separation distance vanishes. We find that in general relativity, the interaction between portal mouths is not primarily gravitational in nature, but depends critically on matter interactions.

The analysis of teleparallel $f(T,{\nabla }_{{\mu }_1}T,\dots ,{\nabla }_{{\mu }_n}\cdots {\nabla }_{{\mu }_1}T)$ gravity in the Jordan and Einstein frames is presented. The equivalence between $f(T,{\nabla }_{{\mu }_1}T,\dots ,{\nabla }_{{\mu }_n}\cdots {\nabla }_{{\mu }_1}T)$ gravity and a scalar-multitensor theory is proved in both frames for systems with a regular Hessian matrix. For each order of derivative an auxiliary tensor of the same order is introduced. As a consequence, the order of the differential equation for the tetrad field is reduced to an equation of order two, but the price to be paid is the analysis of a system of coupled equations for the auxiliary fields.

For ultralight scalar particles like axions, dark matter can form a state of the Bose-Einstein condensate (BEC) with a coherent classical wave whose wavelength is of order galactic scales. In the context of an oscillating scalar field with mass $m$, this BEC description amounts to integrating out the field oscillations over the Hubble timescale $H^{-1}$ in the regime $m\gg H$. We provide a gauge-invariant general relativistic framework for studying cosmological perturbations in the presence of a self-interacting BEC associated with a complex scalar field. In particular, we explicitly show the difference of BECs from perfect fluids by taking into account cold dark matter, baryons, and radiation as a Schutz-Sorkin description of perfect fluids. We also scrutinize the accuracy of commonly used Newtonian treatment based on a quasistatic approximation for perturbations deep inside the Hubble radius. For a scalar field starting to oscillate after matter-radiation equality, we show that, after the BEC formation, a negative self-coupling hardly leads to a Laplacian instability of the BEC density contrast. This is attributed to the fact that the Laplacian instability does not overwhelm the gravitational instability for self-interactions within the validity of the nonrelativistic BEC description. Our analysis does not accommodate the regime of parametric resonance, which can potentially occur for a large field alignment during the transient epoch prior to the BEC formation.

We consider the dark-matter (DM) scenarios consisting of the mixture of weakly interacting massive particles (WIMPs) and primordial black holes (PBHs) and study what fraction of the total DM can be PBHs. In such scenarios, PBHs can accrete the WIMPs and consequently enhance the heating and ionization in the intergalactic medium due to WIMP annihilations. We demonstrate that the CMB data can give stringent bounds on the allowed PBH fraction which are comparable to or even tighter than those from the gamma-ray data depending on the DM masses. For instance, the Markov-chain Monte Carlo likelihood analysis using the Planck CMB data leads to a bound on the PBH DM fraction with respect to the total dark matter $f_{\mathrm{PBH}}\lesssim \mathcal{O}({10}^{-10}\sim {10}^{-8})$ for the WIMP mass $m_{\chi }\sim \mathcal{O}(10\sim {10}^3)\mathrm{GeV}$ with the conventional DM annihilation cross section $⟨\sigma v⟩=3\times {10}^{-26}{\mathrm{c}\mathrm{m}}^3/\mathrm{s}$. We also investigate the feasibility of the global 21-cm signal measurement to provide stringent constraints on the PBH fraction.