In this paper we present two results in ($2+1$) gravity coupled to nonlinear electrodynamics. First we determine the general form of the electromagnetic field tensor in ($2+1$) gravity coupled to nonlinear electrodynamics in stationary cyclic spacetimes. Secondly, we determine a family of exact solutions in ($2+1$) gravity sourced by a nonlinear electromagnetic field. The solutions are characterized by five parameters: mass $M$, angular momentum $J$, cosmological constant $\mathrm{\Lambda }$, and two electromagnetic charges $q_{\alpha }$ and $q_{\beta }$. Remarkably, the solution can be interpreted as a traversable wormhole, provided the fulfillment of certain inequalities by the characteristic parameters; fine-tuning of the cosmological constant leads to an extreme black hole, whereas by switching off one of the electromagnetic charges, we obtain the Bañados-Teitelboim-Zanelli (BTZ) black hole.

In general relativity and many modified theories of gravity, isolated black holes (BHs) cannot source massless scalar fields. Einstein-Maxwell-dilaton (EMd) theory is an exception: through couplings both to electromagnetism and (nonminimally) to gravity, a massless scalar field can be generated by an electrically charged BH. In this work, we analytically model the dynamics of binaries comprised of such scalar-charged (“hairy”) BHs. While BHs are not expected to have substantial electric charge within the standard model of particle physics, nearly extremally charged BHs could occur in models of minicharged dark matter and dark photons. We begin by studying the test-body limit for a binary BH in EMd theory, and we argue that only very compact binaries of nearly extremally charged BHs can manifest nonperturbative phenomena similar to those found in certain scalar-tensor theories. Then, we use the post-Newtonian approximation to study the dynamics of binary BHs with arbitrary mass ratios. We derive the equations governing the conservative and dissipative sectors of the dynamics at next-to-leading order, use our results to compute the Fourier-domain gravitational waveform in the stationary-phase approximation, and compute the number of useful cycles measurable by the Advanced LIGO detector. Finally, we construct two effective-one-body (EOB) Hamiltonians for binary BHs in EMd theory: one that reproduces the exact test-body limit and another whose construction more closely resembles similar models in general relativity, and thus could be more easily integrated into existing EOB waveform models used in the data analysis of gravitational-wave events by the LIGO and Virgo collaborations.

When two spacetimes are stitched across a null shell placed at the horizon of a black hole, Bondi-Metzner-Sachs (BMS) supertranslation-like soldering freedom arises if one demands the induced metric on the shell should remain invariant under the translations generated by the null generators of the shell. We revisit this phenomenon on the horizon of rotating shells and obtain BMS-like symmetries. We further show that superrotation-like soldering symmetries in the form of conformal isometries can emerge whenever the degenerate metric of any null hypersurface admits a dependency on a null (degenerate direction) coordinate. This kind of conformal isometry can also appear for a null surface situated very close to the horizon of black holes. We also study the intrinsic properties of different kinds of horizon shells considered in this article.

In a four dimensional inflation theory, a persistent electric field can be established by making the inflaton coupled to the gauge field like a dilaton. We investigate the pair production of scalar particles in the inflaton-driven electric field. In particular, we evaluate the induced current due to the pair production. The presence of the dilatonic coupling ensures the validity of the Wentzel-Kramers-Brillouin approximation at the past and the future infinities, without tuning constant parameters. Thus, the semiclassical description is applicable in evaluating the induced current. Solving the field equations with the induced current, we evaluate the first-order backreaction to the electric field. It turns out that the electric field decreases with the cosmic expansion. The result indicates that the no-anisotropic hair theorem for inflation holds true regardless of whether the dilatonic coupling is present or not.

We study the effects of the Gauss-Bonnet term on the energy spectrum of inflationary gravitational waves. The models of inflation are classified into two types based on their predictions for the tensor power spectrum: red-tilted ($n_T<0$) and blue-tilted spectra ($n_T>0$), respectively, and then the energy spectra of the gravitational waves are calculated for each type of model. We find that the gravitational wave spectra are enhanced depending on the model parameter if the predicted inflationary tensor spectra have a blue tilt, whereas they are suppressed for the spectra that have a red tilt. Moreover, we perform the analyses on the reheating parameters involving the temperature, the equation-of-state parameter, and the number of $e$-folds using the gravitational wave spectrum. Our results imply that the Gauss-Bonnet term plays an important role not only during inflation but also during reheating whether the process is instantaneous or lasts for a certain number of $e$-folds until it thermalizes and eventually completes.

We investigate the impact of the post-inflationary thermal histories on the cosmic graviton spectrum caused by the inflationary variation of their refractive index. Depending on the frequency band, the spectral energy distribution can be mildly red, blue, or even violet. Wide portions of the parameter space lead to potentially relevant signals both in the audio range (probed by the advanced generation of terrestrial interferometers) and in the mHz band (where space-borne detectors could be operational within the incoming score year). The description of the refractive index in conformally related frames is clarified.

We reanalyze the detection possibilities for gravitational waves arising from cosmological first order phase transitions. We discuss the stochastic gravitational wave background corresponding to the three expected scenarios of phase transition dynamics. We then perform an analysis on the detection possibilities for each case using sensitivities for the next generation ground-based detector Cosmic Explorer and the current LISA proposal, using two analysis methods. We find that having both detectors allows wide detection possibilities over much of the parameter space, including those corresponding to several early Universe models.

As first suggested by U. Fano in the 1940s, the statistical fluctuation of the number of pairs produced in an ionizing interaction is known to be sub-Poissonian. The dispersion is reduced by the so-called “Fano factor,” which empirically encapsulates the correlations in the process of ionization. In modeling the energy response of an ionization measurement device, the effect of the Fano factor is commonly folded into the overall energy resolution. While such an approximate treatment is appropriate when a significant number of ionization pairs are expected to be produced, the Fano factor needs to be accounted for directly at the level of pair creation when only a few are expected. To do so, one needs a discrete probability distribution of the number of pairs created $N$ with independent control of both the expectation $\mu$ and Fano factor $F$. Although no distribution $P(N|\mu ,F)$ with this convenient form exists, we propose the use of the COM-Poisson distribution together with strategies for utilizing it to effectively fulfill this need. We then use this distribution to assess the impact that the Fano factor may have on the sensitivity of low-mass WIMP search experiments.

Lasing of an ultralight axion condensate into photons can be sensitive to the presence of a background plasma owing to its coupling to electromagnetism. Such a scenario is particularly relevant for a superradiant axion condensate around stellar mass black holes since the axion mass can be within a few orders of magnitude of the plasma frequency of the surrounding medium. In this paper, I discuss the properties of the plasma around a black hole and analyze its effects on the lasing of a uniform axion condensate of mass of the order of the plasma frequency.

We perform spherically symmetric simulations of the core collapse of a single progenitor star of zero age main sequence mass $M_{\mathrm{ZAMS}}=15M_{\odot }$ with two models of heavy sterile neutrinos in the mass range of $100\mathrm{MeV}/c^2$. According to both models, these hypothetical particles are copiously produced in the center, stream outwards and subsequently decay, releasing energy into final states (including neutrinos) of the Standard Model. We find that they can lead to a successful explosion in otherwise nonexploding progenitors. Depending on their unknown parameters (e.g., mass and coupling constants with matter), we obtain either no explosion or an explosion of one of two types, i.e., through heating of gas downstream of the stalled shock wave, similar to the standard scenario for supernova explosions, or through heating of gas at higher radii that ejects matter from the outer core or the envelope while the center continues to accrete matter. In both cases, the explosion energies can be very high. We presume that this new type of explosion would produce an electromagnetic signal that significantly differs from common events because of the relative absence of heavy elements in the ejecta. The combination of core-collapse simulations and astrophysical observations may further constrain the parameters of the sterile neutrinos.

Caustic rings of dark matter with tricusp cross section were predicted to lie in the galactic disk. Their radii increase on cosmological time scales at a rate of order $1\mathrm{kpc}/\mathrm{Gyr}$. When a caustic ring passes through the orbit of a star, the orbit is strongly perturbed. We find that a star moving in a nearly circular orbit is first attracted towards the caustic ring, then moves with and oscillates about the caustic for approximately 1 Gyr before returning to its original orbit. As a result, a stellar overdensity forms around the caustic ring. We predict such overdensities to be of order 120% near the second caustic ring where the Monoceros Ring is observed and of order 45%, 30% and 15% near the third, fourth and fifth caustic rings, respectively. We show that the associated bulk velocities of the stars near the caustic rings are less than a few $\mathrm{km}/\mathrm{s}$. We also determine the density profile of interstellar gas near the fifth caustic ring assuming it is in thermal equilibrium in the gravitational potential of the caustic and of the gas itself.

Collapsing supermassive stars (SMSs) with masses $M\gtrsim {10}^{4–6}{M}_{\odot }$ have long been speculated to be the seeds that can grow and become supermassive black holes (SMBHs). We previously performed general relativistic magnetohydrodynamic (GRMHD) simulations of marginally stable $\mathrm{\Gamma }=4/3$ polytropes uniformly rotating at the mass-shedding limit and endowed initially with a dynamically unimportant dipole magnetic field to model the direct collapse of SMSs. These configurations are supported entirely by thermal radiation pressure and reliably model SMSs with $M\gtrsim {10}^6{M}_{\odot }$. We found that around 90% of the initial stellar mass forms a spinning black hole (BH) remnant surrounded by a massive, hot, magnetized torus, which eventually launches a magnetically-driven jet. SMSs could be therefore sources of ultra-long gamma-ray bursts (ULGRBs). Here we perform GRMHD simulations of $\mathrm{\Gamma }\gtrsim 4/3$, polytropes to account for the perturbative role of gas pressure in SMSs with $M\lesssim {10}^6{M}_{\odot }$. We also consider different initial stellar rotation profiles. The stars are initially seeded with a dynamically weak dipole magnetic field that is either confined to the stellar interior or extended from its interior into the stellar exterior. We calculate the gravitational wave burst signal for the different cases. We find that the mass of the black hole remnant is 90%–99% of the initial stellar mass, depending sharply on $\mathrm{\Gamma }-4/3$ as well as on the initial stellar rotation profile. After $t\sim 250–550M\approx 1-2\times {10}^3(M/{10}^6{M}_{\odot })\mathrm{s}$ following the appearance of the BH horizon, an incipient jet is launched and it lasts for $\sim {10}^4–{10}^5(M/{10}^6{M}_{\odot })\mathrm{s}$, consistent with the duration of long gamma-ray bursts. Our numerical results suggest that the Blandford-Znajek mechanism powers the incipient jet. They are also in rough agreement with our recently proposed universal model that estimates accretion rates and electromagnetic (Poynting) luminosities that characterize magnetized BH-disk remnant systems that launch a jet. This model helps explain why the outgoing electromagnetic luminosities computed for vastly different BH-disk formation scenarios all reside within a narrow range ($\sim {10}^{52\pm 1}\mathrm{erg}{\mathrm{s}}^{-1}$), roughly independent of $M$.

The thermodynamic geometry formalism is applied to strongly interacting matter to estimate the deconfinement temperature. The curved thermodynamic metric for QCD is evaluated on the basis of lattice data, whereas the hadron resonance gas model is used for the hadronic sector. Since the deconfinement transition is a crossover, the geometric criterion used to define the (pseudo)critical temperature, as a function of the baryonchemical potential ${\mu }_B$, is $R(T,{\mu }_B)=0$, where $R$ is the scalar curvature. The (pseudo)critical temperature, $T_c$, resulting from QCD thermodynamic geometry is in good agreement with lattice and phenomenological freeze-out temperature estimates. The crossing temperature, $T_h$, evaluated by the hadron resonance gas, which suffers from some model dependence, is larger than $T_c$ (about 20%) signaling remnants of confinement above the transition.

We analyze the $\mathcal{N}=1$ supersymmetric Wess-Zumino model dimensionally reduced to the $\mathcal{N}=2$ supersymmetric model in three Euclidean dimensions. As in the original model in four dimensions and the $\mathcal{N}=(2,2)$ model in two dimensions the superpotential is not renormalized. This property puts severe constraints on the nontrivial fixed-point solutions, which are studied in detail. We admit a field-dependent wave function renormalization that in a geometric language relates to a Kähler metric. The Kähler metric is not protected by supersymmetry and we calculate its explicit form at the fixed point. In addition we determine the exact quantum dimension of the chiral superfield and several critical exponents of interest, including the correction-to-scaling exponent $\omega$, within the functional renormalization group approach. We compare the results obtained at different levels of truncation, exploring also a momentum-dependent wave function renormalization. Finally we briefly describe a tower of multicritical models in continuous dimensions.

We propose a minimal realization of the Peccei-Quinn mechanism in a realistic SU(5) model, where the axion mass is directly connected to the grand unification scale. Accounting for constraints from proton decay, collider searches and gauge coupling unification, we predict the axion mass $m_a\in [4.8,6.6]\mathrm{neV}$. The upper bound relaxes to $m_a<330\mathrm{neV}$ for a tuned flavor structure of the proton decay operators. The predicted mass window will be complementarily probed by the axion dark matter experiments ABRACADABRA and CASPER-Electric, which could provide indirect evidence for the scale of grand unification before the observation of proton decay.

We show that in the absence of trilinear terms in the scalar potential of the Georgi-Machacek model, heavy charged scalars do not necessarily decouple from the $h\to \gamma \gamma$ decay amplitude. In such scenarios, measurement of the Higgs to diphoton signal strength can place stringent constraints in the parameter space. Using the projected precisions at the High Luminosity LHC (HL-LHC) and the ILC, we find that the upper bound on the triplet vacuum expectation value can be as low as 10 GeV. We also found that when combined with the theoretical constraints from perturbative unitarity and stability, such variants may be ruled out altogether.

Models with extra gauge symmetry are well-motivated extensions of the Standard Model. In this paper, we study an extended gauge model with a heavy neutral gauge boson $Z^{\prime }$ which is fermiophobic. Thus, the production of such particles can occur via vector boson fusion, with subsequent decays into $WW$ or $Zh$. We investigate the collider phenomenology of such $Z^{\prime }\mathrm{s}$ in the context of both the 14 TeV LHC and the future Compact Linear Collider. We find that looking at $\ell \ell bb$ final states provides a rich opportunity to discover such new vector bosons where conventional search strategies in the dilepton channel would fail. In particular, we optimize our analysis by putting in kinematic cuts deriving model-independent values of $\sigma \times \mathrm{BR}$ needed for a $5\sigma$ discovery at the LHC. We then translate this into the parameter space of a specific model for illustration purpose—our results show that fermiophobic $Z^{\prime }$s are discoverable in the $\ell \ell bb$ channel for a wide range of parameter values.

We report a strong tension in ${ϵ}_K$ at the $4\sigma$ level between the experimental value and the theoretical value calculated directly from the standard model using lattice QCD inputs such as ${\widehat{B}}_K$, $|V_{cb}|$, $|V_{us}|$, ${\xi }_0$, ${\xi }_2$, ${\xi }_{\mathrm{LD}}$, $F_K$, and $m_c$. The standard model with lattice QCD inputs describes only 70% of the experimental value of ${ϵ}_K$, and does not explain its remaining 30%. We also find that this tension disappears when we use the inclusive value of $|V_{cb}|$ (results of the heavy quark expansion based on QCD sum rules) to determine ${ϵ}_K$. This tension is highly correlated with the present discrepancy between the exclusive and inclusive values of $|V_{cb}|$. In order to resolve, in part, the issue with $|V_{cb}|$, it would be highly desirable to have a comprehensive reanalysis over the entire set of experimental data on the $\overline{B}\to D^{*}\ell \overline{\nu }$ decays using an alternative parametrization of the form factors, such as the Boyd, Grinstein, and Lebed parametrization, and a comparison with results of the Caprini, Lellouch, and Neubert method.

The impact of $SU(3)$ center vortices on the gluon propagator in Landau gauge is investigated on original, vortex-removed and vortex-only lattice gauge field configurations. Vortex identification is found to partition the gluon propagator into short-range strength on the vortex-removed configurations and long-range strength on the vortex-only configurations. The effect of smoothing vortex-only configurations is also studied, and a regime for recovering the form of the smoothed original propagator from vortex-only configurations is introduced. The results reinforce the significance of center vortices in a fundamental understanding of QCD vacuum structure.