Dark Charge Research Articles

Dark photon superradiance quenched by dark matter

Black-hole superradiance has been used to place very strong bounds on a variety of models of ultralight bosons such as axions, new light scalars, and dark photons. It is common lore to believe that superradiance bounds are broadly model independent and therefore pretty robust. In this work we show however that superradiance bounds on dark photons can be challenged by simple, compelling extensions of the minimal model. In particular, if the dark photon populates a larger dark sector and couples to dark fermions playing the role of dark matter, then superradiance bounds can easily be circumvented, depending on the mass and (dark) charge of the dark matter.

Effect of Li-doped TiO2 layer on the photoelectric performance of carbon-based CsPbIBr2 perovskite solar cell

Carbon-based CsPbIBr2 perovskite solar cells (PSCs) have attracted much attention due to their excellent photoelectric properties and low cost fabrication processes. The TiO2 has been diffusely employed as electron-transporting layer (ETL) for carbon-based CsPbIBr2 PSC. However, the lower electron mobility for TiO2 restricts the performance improvement. The tactics of ion doping is normally used to improve the ETL performance. In this study, Li-doped TiO2 (Li: TiO2) is used as a novel ETL for carbon-based planar CsPbIBr2 PSC. There is no change in the optical band gap of TiO2 after the incorporation of Li. However, Li-doping can effectively improve the crystallinity of TiO2 film and reduce the dark current and charge recombination of CsPbIBr2 PSC. Comparing with the TiO2-based CsPbIBr2 PSC, the efficiency of CsPbIBr2 PSC with the Li: TiO2 ETL increases from 6.63% to 8.09%. Additionally, the use of the Li: TiO2 ETL also has a positive impact on the long-term stability of the CsPbIBr2 PSC. This work indicates that ion doping can offer a new route to produce effective ETL for the development of highly-efficient CsPbIBr2 solar cell with a interface engineering concept.

Special cases of the multi-measure model – Understanding the prolonged inflation

The multi-measure model (MMM), in which one modifies the action to include both the Riemannian measure and a non-Riemannian one, has proven to be able to produce viable Universe evolution scenarios. In this article we consider two special cases of the multi-measure model, in which we first decouple the two kinetic terms in the Lagrangian entirely and later remove the dark charge of the model. We show numerically that those special cases still possess the needed evolutionary stages of the Universe and furthermore, for them one can obtain a sufficient number of e-folds of the early inflation. In the first case, the inflaton still moves backwards on the effective potential during inflation, while in the second, it does not, meaning that this behavior comes from the dark charge. We connect the model with hyperinflationary models and investigate how the different epochs are born from the interplay between the two scalar fields. We demonstrate that there is a dynamically induced slow-roll epoch, which is prolonged by the complicated movement of the two scalars in the field space. Finally, we show that while the adiabatic speed of sound can become imaginary, the phase speed of sound remains real.

Kinetic mixing, dark Higgs triplets, and MW

The kinetic mixing (KM) portal is a popular mechanism that allows light dark matter (DM) in the mass range below $\ensuremath{\sim}1\text{ }\text{ }\mathrm{GeV}$ to achieve the observed relic density by thermal means and can be effectively described by only a few parameters, e.g., $\ensuremath{\epsilon}$, the strength of this KM. In the simplest setup, the Standard Model (SM) $U(1{)}_{Y}$ hypercharge gauge boson and a $U(1{)}_{D}$ dark photon (DP), which only couples to fields in the dark sector, experience KM via loops of portal matter (PM) fields which have both SM and dark charges, thus generating a small coupling between us and dark matter (DM). However, if one wishes to understand the underlying physics behind this idea in a deeper fashion we need to take a step upward to a more UV-complete picture. Meanwhile, CDFII has measured a value for the $W$-boson mass which lies significantly above SM expectations. In this paper, we speculate that this shift in the $W$'s mass may be related to the $\ensuremath{\sim}1\text{ }\text{ }\mathrm{GeV}$ mass of the DP within a framework of scalar PM that leads to phenomenologically interesting values of $\ensuremath{\epsilon}$ via non-Abelian KM due to the existence of an $SU(2{)}_{L}$, $Y=0$, complex Higgs triplet which carries a nonzero value of the $U(1{)}_{D}$ dark charge. Possible gauge boson plus missing energy signatures of this scenario that can appear at the LHC and elsewhere are examined. Indeed, with modest assumptions, all of the new scalar PM states are predicted to have masses below roughly $\ensuremath{\simeq}630\text{ }\text{ }\mathrm{GeV}$ and so should be at least kinematically accessible. The HL-LHC will very likely to be able to explore all of this model's allowed parameter space.

Dequantization of electric charge: Probing scenarios of cosmological multi-component dark matter

Since the electric charge in the standard model is theoretically not quantized, we may have a variant of it, called dark charge. Similar to the electric charge, the dark charge neither commutes nor closes algebraically with SU(2)L. The condition of algebraic closure leads to a novel gauge extension, SU(2)L⊗U(1)Y⊗U(1)N, where Y and N determine the electric and dark charges, respectively, apart from the color group. We argue that the existence of the dark charge, thus N, leads to novel scenarios of multi-component dark matter, in general. The dark matter stability is determined by a residual (or dark charge) gauge symmetry isomorphic to an even Zk discrete group, where k is specified dependent on the value of the neutrino dark charge. This residual symmetry divides the standard model particles into distinct classes, which possibly accommodate dark matter, but each dark matter candidate cannot decay due to the color and electric charge conservation. We analyze in detail three specific models according to k=2,4,6 and determine the simplest dark matter candidates. For small U(1)N coupling, the two-component dark matter scenarios implied by the dark charge successfully explain the dark matter relic density and the recent XENON1T excess, as well as the beam dump, neutrino scattering, and astrophysical bounds. Otherwise, for large U(1)N coupling, we have multi-WIMPs coexisted beyond the weak scale.

Dark charge versus electric charge

We revisit a theory that proposes a dark charge, $D$, as a dequantization of the electric charge, $Q$. We find that the general arguments of anomaly cancelation and fermion mass generation yield both $D$ and $Q$, nontrivially unified with the weak isospin $T_i$ $(i={1,2,3})$ in a novel gauge symmetry, $SU(3)_C\otimes SU(2)_L\otimes U(1)_Y\otimes U(1)_N$, where $Y$ and $N$ determine $Q$ and $D$ through the $T_3$ operator, i.e. $Q=T_3+Y$ and $D=T_3+N$, respectively. A new observation is that fundamental particles possess a dynamical dark charge which governs both neutrino mass and dark matter, where the neutrino mass is determined via a canonical seesaw, while the dark matter stability is ensured by electric and color charge conservations. We examine the mass spectra of fermions, scalars, and gauge bosons, as well as their interactions, taking into account the kinetic mixing effect of $U(1)_{Y,N}$ gauge fields. The new physics phenomena at colliders are examined. The dark matter relic density and detection are discussed.

Gauge Origin of Double Dark Parity and Implication for Dark Matter

Dark matter must be stabilized over the cosmological timescale, which demands the existence of a stabilizing symmetry, derived by a dark charge, $D$. The existence of this dark charge may affect the quantization of electric charge, which theoretically shifts the electric charge, thus the hypercharge to a novel gauge extension, $SU(3)_C\otimes SU(2)_L\otimes U(1)_Y\otimes U(1)_N$, where $N$ determines $D=T_3+N$, similar to $Q=T_3+Y$. New observation of this work is that the dark charge is broken down to two kinds of dark parity, $Z_2$ and $Z'_2$, which subsequently imply three scenarios of dark matter. The relic density and direct detection for the scenario of two-component dark matter are investigated in detail.

Merger rate of charged black holes from the two-body dynamical capture

We consider the two-body dynamical capture of black holes carrying U(1) charge which can not only correspond to electric or magnetic charge but also have other physical interpretations such as dark or hidden charge. In the low-velocity and weak-field regime, we study gravitational and electromagnetic radiations from point masses with U(1) charges in a hyperbolic orbit, and we develop a formalism to derive the merger rate of charged black holes from the two-body dynamical capture. We apply the formalism to find the effects of the charge-to-mass ratio on the merger rate for possible different cases and discover that the effects depend on the models.

Imaging dark charge emitters in diamond via carrier-to-photon conversion.

The application of color centers in wide-bandgap semiconductors to nanoscale sensing and quantum information processing largely rests on our knowledge of the surrounding crystalline lattice, often obscured by the countless classes of point defects the material can host. Here, we monitor the fluorescence from a negatively charged nitrogen-vacancy (NV−) center in diamond as we illuminate its vicinity. Cyclic charge state conversion of neighboring point defects sensitive to the excitation beam leads to a position-dependent stream of photo-generated carriers whose capture by the probe NV− leads to a fluorescence change. This “charge-to-photon” conversion scheme allows us to image other individual point defects surrounding the probe NV, including nonfluorescent “single-charge emitters” that would otherwise remain unnoticed. Given the ubiquity of color center photochromism, this strategy may likely find extensions to material systems other than diamond.

Boosting Photothermal Theranostics via TICT and Molecular Motions for Photohyperthermia Therapy of Muscle‐Invasive Bladder Cancer (Adv. Healthcare Mater. 24/2021)

Photothermal Therapies In article number 2101063 by Qian Liu, Guangxue Feng, Dan Ding, and co-workers, a small photothermal molecule with active intramolecular motions and a dark state twisted intramolecular charge transfer feature is designed to boost the photothermal conversion ability. Such a design strategy enables the effective low-temperature photo-hyperthermia treatment of muscle-invasive bladder cancers at low drug and laser dosages with minimal side effects.

Solar reflection of dark matter

The scattering of light dark matter off thermal electrons inside the Sun produces a ``fast'' subcomponent of the dark matter flux that may be detectable in underground experiments. We update and extend previous work by analyzing the signatures of dark matter candidates which scatter via light mediators. Using numerical simulations of the dark matter-electron interaction in the solar interior, we determine the energy spectrum of the reflected flux, and calculate the expected rates for direct detection experiments. We find that large Xenon-based experiments (such as XENON1T) provide the strongest direct limits for dark matter masses below a few MeV, reaching a sensitivity to the effective dark matter charge of $\ensuremath{\sim}{10}^{\ensuremath{-}9}e$.

Bounding dark charges on binary black holes using gravitational waves

In models of minicharged dark matter associated with a hidden $U(1)$ symmetry, astrophysical black holes may acquire a "dark" charge, in such a way that the inspiral dynamics of binary black holes can be formally described by an Einstein-Maxwell theory. Charges enter the gravitational wave signal predominantly through a dipole term, but their effect is known to effectively first post-Newtonian order in the phase, which enables measuring the size of the charge-to-mass ratios, $|q_i/m_i|$, $i = 1,2$, of the individual black holes in a binary. We set up a Bayesian analysis to discover, or constrain, dark charges on binary black holes. After testing our framework in simulations, we apply it to selected binary black hole signals from the second Gravitational Wave Transient Catalog (GWTC-2), namely those with low masses so that most of the signal-to-noise ratio is in the inspiral regime. We find no evidence for charges on the black holes, and place typical 1-$\sigma$ bounds on the charge-to-mass ratios of $|q_i/m_i| \lesssim 0.2 - 0.3$.

Accelerated expansion induced by dark matter with two charges

ABSTRACT The accelerated expansion of the Universe has been established through observations of supernovae, the growth of structure, and the cosmic microwave background. The most popular explanation is Einstein's cosmological constant, or dynamic variations hereof. A recent paper demonstrated that if dark matter particles are endowed with a repulsive force proportional to the internal velocity dispersion of galaxies, then the corresponding acceleration of the Universe may follow that of a cosmological constant fairly closely. However, no such long-range force is known to exist. A concrete example of such a force is derived here, by equipping the dark matter particles with two new dark charges. This result lends support to the possibility that the current acceleration of the Universe may be explained without the need for a cosmological constant.

Curved space and particle physics effects on the formation of Bose–Einstein condensation around a Reissner–Nordstrøm black hole

We consider two scalar fields interacting through a \(\chi ^*\chi \phi ^*\phi \) term in the presence of a Reissner–Nordstrøm black hole. Initially, only \(\chi \) particles are present. We find that the produced \(\phi \) particles are localized in a region around the black hole and have a tendency toward condensation provided that \(\phi \) particles are much heavier than the \(\chi \) particles. We also find that such a configuration is phenomenologically viable only if the scalars and the black hole have dark electric charges.

Dynamics of charged anisotropic spherical collapse in energy-momentum squared gravity

This paper investigates the dynamics of charged spherical collapse with anisotropic matter configuration in the context of energy-momentum squared gravity. This newly developed proposal resolves the big-bang singularity and yields the physically viable cosmological results in the early time universe. We establish dynamical equations through Misner-Sharp technique and analyze the effects of charge, anisotropy, effective matter variables and dark source terms on the collapse rate. A relation between Weyl scalar, fluid parameters and dark source terms is also established. The spacetime is not conformally flat due to the presence of anisotropic pressure, multivariate functions and their derivatives. In order to obtain conformally flat spacetime, we consider a specific model of this gravity, neglect the impact of charge and assume the isotropic matter distribution which yields homogeneity of the energy density and conformally flat spacetime. We conclude that positive dark source terms, anisotropy and charge yield the action of a repulsive force which enhances the stability of the system and hence diminishes the collapse rate.

General Relativistic Simulations of the Quasicircular Inspiral and Merger of Charged Black Holes: GW150914 and Fundamental Physics Implications

We perform general-relativistic simulations of charged black holes targeting GW150914. We show that the inspiral is most efficient for detecting black hole charge through gravitational waves and that GW150914 is compatible with having charge-to-mass ratio as high as 0.3. Our work applies to electric and magnetic charge and to theories with black holes endowed with U(1) (hidden or dark) charges. Using our results, we place an upper bound on the deviation from general relativity in the dynamical strong-filed regime of Moffat's modified gravity.

PHOTO-CATALYSIS PROCESSES IN NON-REGULAR MEDIA

Technologies that cause the least harm to nature from global warming standpoint are becoming called-for. In this regard, photo-catalysis which uses the solar energy for chemical transformations of substances is of great interest for studying possible mechanisms of such processes. At the same time, the use of photo-catalysis significantly expands capabilities of the synthesis of new organic and inorganic materials. Charge phototransfer is always at the heart of photochemical transformations. Such processes can be considered from the point of view of quantum mechanics, and the probability of various mechanisms of the passing processes can be calculated using the apparatus of Green's functions. Analytical expressions for kinetic parameters of the charge transfer process between polyatomic particles in non-regular condensed medium and expressions for the extinction coefficient for appropriate processes of charge photo-transfer are obtained. Based on the analysis of obtained analytical expressions of dark and optical charge transfer processes, correlations between kinetic parameters of these processes are obtained. A methodology for determining kinetic parameters of the charge photo-transfer process on the basis of the shape of light absorption curve by means of the system functioning as the frequency of absorbed photons in various systems is presented. In this respect the general methodology has been applied to various specific processes. A methodology for determining the kinetic parameters of the charge phototransfer process from the shape of the light absorption curve by the system as a function of the frequency of absorbed photons in various systems is presented. The general methodology presented has been applied to various specific processes.

The Bright Side and Dark Side of Hybrid Organic–Inorganic Perovskites

The previously developed bistable amphoteric native defect (BAND) model is used for a comprehensive explanation of the unique photophysical properties and for understanding the remarkable performance of perovskites as photovoltaic materials. It is shown that the amphoteric defects in donor (acceptor) configuration capture a fraction of photoexcited electrons (holes) dividing them into two groups: higher energy bright and lower energy dark electrons (holes). The spatial separation of the dark electrons and the dark holes and the k-space separation of the bright and the dark charge carriers reduce electron hole recombination rates, emulating the properties of an ideal photovoltaic material with a balanced, spatially separated transport of electrons and holes. The BAND model also offers a straightforward explanation for the exceptional insensitivity of the photovoltaic performance of polycrystalline perovskite films to structural and optical inhomogeneities. The blue-shifted radiative recombination of bright electrons and holes results in a large anti-Stokes effect that provides a quantitative explanation for the spectral dependence of the laser cooling effect measured in perovskite platelets.

Screening away the H0 tension

This Essay explores consequences of a dark nonlinear electromagnetic sector in a universe with a net dark charge for matter. The cosmological dynamics can be described by a Lemaître model and can be understood, thanks to a screening mechanism driven by the electromagnetic nonlinearities that suppress the dark force on small scales. Only at low redshift, when the screening scale enters the Hubble horizon, do cosmological structures commence to feel the dark repulsion. This repulsive force enhances the local value of the Hubble constant, thus providing a promising scenario for solving the Hubble tension. Remarkably, the dark electromagnetic interaction can have a crucial impact on peculiar velocities, i.e. introducing a bias in their reconstruction methods, and having the potential to explain the presence of a dark flow.

Flipping principle for neutrino mass and dark matter

Flipping a symmetry often leads to a more fundamental symmetry and new physics insight. Applying this principle to the standard model electroweak symmetry, we obtain a novel gauge symmetry, which defines dark charge besides electric charge, neutrino mass mechanism, and resultant dark parity as residual flipped symmetry. The dark parity divides the model particles into two classes: odd and even. The dark matter candidate transforms as a fermion or a scalar singlet, having a mass below the electron mass, being stabilized by the dark parity. Scenarios for consistent neutrino mass generation and dark matter relic are proposed. The nature and further implication of the flipping approach are determined.