It is known that only a narrow plasma wakefield sliver in the electron-beam-driven blowout regime suits positron acceleration. Using 3D simulations, we show that matching the cyclotron frequency ω_c with the plasma frequency ω_p forms a stable electron column on axis, expanding the suitable phase space for positron acceleration sizably. For a plasma density n_p = 10^16 cm^-3 in a 35 T field, the interval expands 4.3 times, and a witness positron beam gains 100–150 MeV over 6 cm (1.6–2.5 GeV/m) with a 92% capture rate.

Fermion condensate inflation, where inflation emerges from four-fermion interactions induced by spacetime torsion, removes the need for additional scalar fields beyond the Standard Model. In this framework, the fermion field can be decomposed into two distinguished sectors, each giving rise to bound states. After integrating out fermions, the bound fields play the roles of the inflaton and the auxiliary fields, resembling hybrid inflation with a waterfall mechanism. The inclusion of an axial chemical potential naturally introduces a mechanism to end inflation and trigger instant preheating. During the waterfall phase, the effective potential of the fermion condensate supports the formation of non-topological solitons such as Q-balls, which act as seeds of primordial black holes. This model is intrinsically connected to Chern-Simons gravity, which implies a parity-violating universe. Consequently, both the primordial black hole (PBH) dark-matter abundance and parity-violation signatures could provide observational tests of the model.

The standard moving mirror model in (1+1)-dimensional spacetime is known to reproduce several quantum aspects of black hole evaporation. A perfectly reflecting, accelerating mirror can emit radiation whose frequency spectrum resembles that of Hawking radiation, although this correspondence holds only under certain approximations. Moreover, the standard in-out formulation does not provide a natural notion of the partner modes associated with the Hawking radiation. In this paper, we reformulate the moving mirror model in terms of Rindler/Milne modes. This formulation not only attributes the origin of the required approximations to mode squeezing effects but also naturally incorporates the notion of partner modes. Furthermore, as a consequence of these mode squeezing effects, the radiation received by an inertial observer at future null infinity exhibits additional nontrivial quantum correlations, even though its frequency spectrum approximately follows a Bose–Einstein or Fermi–Dirac distribution.

We present a new analysis of cosmic dipole anisotropy using gamma-ray bursts (GRBs) as high-redshift standardizable candles. GRBs are ideal probes for testing the cosmological principle thanks to their high luminosity, wide redshift range, and nearly isotropic sky coverage. For the first time, we employ the luminosity-time (L-T) relation, known in the literature as the bidimensional X-ray Dainotti relation, corrected for redshift evolution, to standardize a sample of 176 long GRBs detected by Swift. We test for dipolar modulations in the GRB Hubble diagram using both the Dipole Fit Method and a new approach introduced here, the Anisotropic Residual Analysis Method. Both methods yield consistent results: a dipole amplitude of Ad similar or equal to 0.6 +/- 0.2 pointing towards (RA, DEC) approximate to(134 degrees +/- 30 degrees, -36 degrees +/- 21 degrees) (equatorial coordinates). As shown in the Appendix, this corresponds to a boost velocity of the observer with respect to the GRB rest-frame in the antipodal direction from the dipole direction. Extensive isotropy tests and 20,000 Monte Carlo simulations confirm that the detected signal cannot be explained by chance alignments or by the angular distribution of the GRB sample. We also show how, by incorporating a dipole term, residual correlations are eliminated, showing that the dipole model provides a better fit than standard isotropic Lambda CDM.

3-forms are natural candidates for describing the late-time accelerated expansion of the Universe, as they can inherently reproduce a positive cosmological constant when lacking an evolving potential. When such a potential is present, a 3-form field may exhibit either quintessence-like or phantom-like behaviour. In this paper, we consider a late-time effective dark energy model described by a 3-form with a Gaussian potential, stable during the dark-energy-dominated era. We constrain this model observationally by performing a Markov Chain Monte Carlo (MCMC) analysis employing a comprehensive cosmological dataset, including Planck PR4 cosmic microwave background (CMB) data, DESI DR1 baryon acoustic oscillation (BAO) measurements, Pantheon+ Type Ia supernovae data, low-z Cepheid calibrators, and DES Y1 large-scale structure observations. We demonstrate that the 3-form model successfully increases the predicted Hubble parameter of CMB and BAO data from 67.89 +/- 0.36km/s/Mpc of Lambda CDM model to 68.29+0.56-0.61km/s/Mpc by approaching the potential peak at the right time, thus mildly reducing the tension with the late-time observation. Overall, the 3-form field serves as a promising candidate of phantom-like dark energy from both theoretical and observational points of view.

Why (and how) the Universe was born is one of the ultimate questions in physics. Another big puzzle is about the arrow of time: Why is there only one direction of time? Are these two issues related? One way to solve both puzzles at one stroke is to posit that our Universe was pair-created with a twin, whose time arrow is opposite to ours. If so, then the twins must naturally be quantum entangled. In Euclidean quantum gravity, this implies the existence of a Euclidean wormhole bridging the twin universes. Each universe is then in a mixed state, and the mutual entanglement shall leave signatures in the cosmic microwave background (CMB) power spectrum. Invoking the Klebanov-Susskind-Banks wormhole as a toy model for the sake of tractability, we show that the entanglement selects a novel and unique nonthermal global vacuum for the total inflaton perturbations in both universes. This is equivalent to imposing a simple harmonic oscillator boundary condition on the Euclidean wave function of the total perturbations, and it turns out that the entanglement enhances the CMB power spectrum for long-wavelength modes. Such a birthmark renders our notion refutable.

Commemorating the 2024 S. Chandrasekhar Prize, this review provides a retrospective on the genesis and evolution of plasma wakefield acceleration. It traces the journey from prehistory and the invention of the Plasma Wakefield Accelerator (PWFA), the establishment of its theoretical cornerstones, to its profound reverberations across fundamental physics, including astrophysics and analog gravity. The narrative emphasizes conceptual evolution, key theoretical breakthroughs, and future outlook, culminating in a vision for hybrid schemes and next-generation colliders. In addition to application to particle accelerators and high energy collider physics, it is found that plasma wakefield, with its ultra-intense acceleration, can also be applied to investigate gravity effects in the laboratory based on Einstein's equivalence principle. A specific example is accelerating flying relativistic plasma mirrors to investigate the celebrated black hole Hawking evaporation and the associated information loss paradox. We describe an ongoing experiment, AnaBHEL (Analog Black Hole Evaporation via Lasers), which aims at shedding some lights on the black hole information loss paradox.

We investigate how inflation can emerge from four-fermion interactions generated by spacetime torsion, eliminating the need for additional scalar fields beyond the Standard Model. We partition fermions in two sectors and introduce two bound fields. In the effective theory approach, once all the fermions have been integrated out, the bound fields serve as the inflaton and the auxiliary field, in analogy to the hybrid inflation and accounting for a waterfall (hybrid) mechanism. The inclusion of an axial chemical potential naturally facilitates the end of reheating. During the waterfall regime, the effective potential governing the fermion condensate supports the formation of non-topological solitons, known as Q-balls, which can be accounted for seeding primordial black holes (PBHs).

We introduce a novel fusion scheme enabled by laser-plasma solitons, which promises to overcome several fundamental obstructions to reaching the breakeven condition. For concreteness, we invoke deuterium-tritium (DT) as fuels. The intense electromagnetic field trapped inside the soliton significantly enhances the DT-fusion cross section, its ponderomotive potential evacuates electrons, and it accelerates D/T to kinetic energies suitable for fusion reaction. While electrons are expelled almost instantly, the much heavier D/T moves at picosecond time scale. Such a difference in time scales renders a time window for DT fusion to occur efficiently in an electron-free environment. We inject two consecutive lasers, where the first would excite plasma solitons and the second, much more intense and with a matched lower frequency, would fortify the soliton electromagnetic field resonantly. We impose a plasma density gradient to induce soliton motion. All D/T inside the plasma column swept by the moving soliton during its lifetime would participate in this fusion mechanism. We show that the breakeven condition is attainable. Invoking fiber laser and the iCAN laser technologies for high repetition rate and high intensity operation, gigawatt output maybe conceivable.

Three-form fields provide a theoretically well-motivated framework for dark energy, arising in higher-dimensional theories and exhibiting a rich cosmological phenomenology. We investigate a minimally coupled three-form dark energy model with a Gaussian potential and constrain it using current cosmological observations, including CMB shift parameters, DESI DR2 baryon acoustic oscillation measurements, Pantheon+ supernovae with and without SH0ES calibration, cosmic chronometers, and gamma-ray bursts. Parameter estimation is performed within a Bayesian Markov-chain Monte Carlo framework, while model comparison relies on several information criteria and the Bayesian evidence, as well as tension statistics. We find that the three-form model provides a viable and competitive description of the expansion history of the Universe. It is mildly preferred over ΛCDM for the combination of early and late-time datasets that are heavily tensioned (CMB+BAO and Pantheon+SH0ES). This preference decreases to neutrality for the other, less tensioned combination of early and late-time data, while for individual early-time or late-time datasets analysed separately, the information criteria are neutral or favour ΛCDM. This suggests that the additional degrees of freedom of the three-form field may help accommodate cosmological observations of different origins within a common framework. The reconstructed dark energy dynamics exhibit a characteristic phantom phase at intermediate redshifts while approaching a cosmological-constant-like behaviour at early and late times, providing a distinctive observational signature. Although the model does not significantly alleviate the Hubble tension despite allowing higher values of H_0, it remains consistent with current observations and offers a well-motivated alternative to ΛCDM whose predictions can be tested by future cosmological surveys.

Foreground masking and incomplete sky coverage complicate cosmic microwave background (CMB) polarization analyses by inducing mode coupling and imperfect E/B separation, with particularly strong impact on searches for primordial B modes. We present SkyReconNet-P, a convolutional neural network for inpainting CMB polarization maps that extends the SkyReconNet framework to jointly reconstruct the polarization (Q, U) maps from partial-sky observations. The method combines regional processing with a hybrid design, utilizing standard convolution and dilated convolution to do a multiscale feature integration. We evaluate performance at both the map and power spectrum level using two masking scenarios: a generated random mask and the Planck 2018 common polarization inpainting mask. For both masking scenarios, SkyReconNet-P reproduces the large-scale morphology of the target maps. In power-spectrum space, we find that the reconstructed E mode spectrum closely tracks the target at low multipoles, while small biases emerge at higher l. For B mode, the raw reconstructed spectra exhibit a larger multipole-dependent bias, which we mitigate using a simulation-based linear calibration. We show that the calibrated B-mode spectrum preserves more information by comparing it with spectrum estimation using pseudo-Cl. Finally, we demonstrate cosmological parameter inference from calibrated reconstructed spectra by fitting (r, Alens) with a Gaussian bandpower likelihood, recovering posteriors consistent with injected parameters across three test ensembles down to r similar to 10-3. These results support inpainting as a complementary route to cut-sky approaches when downstream pipelines can greatly benefit from statistically well-characterized, gap-filled polarization maps.

Analog Hawking radiation emitted by a perfectly reflecting mirror in (1 + 3)-dimensional flat spacetime is investigated. This is accomplished by studying the reflected frequency and momentum based on Einstein's mirror, instead of the canonical way of solving, if possible, wave equations subjected to a dynamical Dirichlet boundary condition. In the case of a finite-size mirror, diffraction pattern appears in the radiation spectrum. Based on the relevant parameters in the proposed analog black hole evaporation via lasers experiment, in which the Hawking temperature T-H similar or equal to 0.03 eV and the mirror area A similar or equal to (50 mu m)(2), the Hawking photon yield is estimated to be N similar or equal to 16/laser shot.

We investigate the cosmological observables using the Euclidean path integral approach. Specifically, we study both the no-boundary compact instantons scenario and the Euclidean wormholes scenario that can induce the creation of two universes from nothing. It is known that perturbations associated with the noboundary scenario can only be consistent with the Bunch-Davies vacuum. Here we conjecture that the Euclidean wormholes can allow for a class of de Sitter invariant vacua, the so-called alpha-vacua, where the Bunch-Davies vacuum is a special case. This therefore provides the alpha-vacua a geometrical origin. As an aside, we discuss a subtle phase issue when considering the power spectrum related to alpha-vacua in the closed universe framework.

Plasma physics offers a wide range of fundamental phenomena, making it an excellent subject for undergraduate laboratory instruction. In this work, we present the design, construction, and characterization of a DC glow-discharge plasma chamber developed for the junior-level curriculum, a project carried out by two undergraduate students. The apparatus consists of a 1-meter-long quartz tube with a movable electrode, enabling systematic exploration of plasma behavior under varying pressure, voltage, and geometry. Using this platform, we characterized the Paschen breakdown relation and the voltage-current characteristics of the plasma. We then developed Langmuir probes to map spatial distributions of electron temperature and density, and used Boltzmann plot spectroscopy to measure excitation temperatures across different plasma regions. Finally, with custom Helmholtz coils, we demonstrated magnetic focusing of electrons. We performed Runge-Kutta simulations of particle trajectories and analyzed the electron drift velocity by comparing the focal lengths. Overall, this plasma chamber provides a versatile platform for investigating fundamental plasma phenomena and offers potential for future studies, including microwave-plasma interactions and other student-driven investigations.

Accurate prediction of particle creation from accelerating mirrors is crucial for interpreting forthcoming analog Hawking radiation experiments such as AnaBHEL. However, realistic experimental setups render the associated Bogoliubov integrals analytically intractable. To address this challenge, we introduce the Inertial Replacement Method (IRM), a hybrid analytic-numerical framework for computing Bogoliubov coefficients for general moving-mirror trajectories. The IRM replaces the asymptotically inertial portions of a trajectory with analytic inertial extensions, so that numerical evaluation is required only for the finite accelerating segment. We derive perturbative error bounds for both perfectly and imperfectly reflecting mirrors, providing controlled accuracy estimates and guiding the choice of segmentation thresholds. The method is validated against analytically solvable trajectories and then applied to a fully numerical, PIC-based Chen-Mourou plasma-mirror trajectory relevant to the planned AnaBHEL experiment. A key physical insight emerging from this analysis is that the radiation spectrum is determined almost entirely by the finite accelerating region, with negligible sensitivity to the far-past and far-future inertial motion. These results establish the IRM as a reliable and broadly applicable computational tool for modeling particle creation in realistic analog-gravity systems such as AnaBHEL.

We introduce a comprehensive, custom-developed neural network, the PUREPath-B, that yields a posterior predictive distribution of Cosmic Microwave Background (CMB) B-mode signal conditioned on the foreground contaminated CMB data and informed by the training dataset. Our network employs nested probabilistic multi-modal U-Net framework, enhanced with probabilistic ResNets at skip connections and seamlessly integrates Bayesian statistics and variational methods to minimize the foreground and noise contaminations. During training, the initial prior distribution over network parameters evolves into approximate posterior distributions through Bayesian inference, constrained by the training data. From the approximate joint full posterior of the model parameters, our network infers a predictive CMB posterior during inference and yields summary statistics such as predictive mean, variance of the cleaned map. The predictive standard deviation provides an interpretable measure of per-pixel uncertainty in the predicted mean CMB map. For loss function, we use a linear combination of KL-Divergence loss and weighted MAE-which ensures that maps with higher amplitudes do not dominate the loss disproportionately. Furthermore, the results from the cosmological parameter estimation using the cleaned B-mode power spectrum, along with its error estimates demonstrates our network minimizes the foreground contaminations effectively, enabling accurate recovery of tensor-to-scalar ratio and lensing amplitude.

We introduce a novel neural network, SkyReconNet, which combines the expanded receptive fields of dilated convolutional layers along with standard convolutions, to capture both the global and local features for reconstructing the missing information in an image. We implement our network to inpaint the masked regions in a full-sky Cosmic Microwave Background (CMB) map. Inpainting CMB maps is a particularly formidable challenge when dealing with extensive and irregular masks, such as galactic masks which can obscure substantial fractions of the sky. The hybrid design of SkyReconNet leverages the strengths of standard and dilated convolutions to accurately predict CMB fluctuations in the masked regions, by effectively utilizing the information from surrounding unmasked areas. During training, the network optimizes its weights by minimizing a composite loss function that combines the Structural Similarity Index Measure (SSIM) and mean squared error (MSE). SSIM preserves the essential structural features of the CMB, ensuring an accurate and coherent reconstruction of the missing CMB fluctuations, while MSE minimizes the pixel-wise deviations, enhancing the overall accuracy of the predictions. The predicted CMB maps and their corresponding angular power spectra align closely with the targets, achieving the performance limited only by the fundamental uncertainty of cosmic variance. The network's generic architecture enables application to other physics-based challenges involving data with missing or defective pixels, systematic artefacts etc. Our results demonstrate its effectiveness in addressing the challenges posed by large irregular masks, offering a significant inpainting tool not only for CMB analyses but also for image-based experiments across disciplines where such data imperfections are prevalent.

This paper presents an enhanced optical configuration for a single-pass quantitative Schlieren imaging system that achieves an optical resolution of approximately 4.6 micrometers. The modified setup decouples sensitivity from resolution, enabling independent optimization of these critical parameters. Using this high-resolution system, we conduct quantitative analyses of supersonic jets emitted from sub-millimeter nozzles into the atmosphere and investigate shock waves induced by knife blades interacting with these jets in a vacuum environment. The fine resolution allows for detailed visualization of shock wave structures and accurate measurement of density gradients. We demonstrate the system's effectiveness by examining the density gradient profile along the shock diamonds and mapping density profiles across shock waves. These density profiles are analyzed for their relevance in laser-plasma applications, including laser wakefield acceleration and the Analog Black Hole Evaporation via Laser (AnaBHEL) experiment. Our findings indicate that this system can help determine key parameters such as peak density, plateau length, and shock wave thickness-essential for optimizing electron acceleration and achieving specific plasma density profiles. This high-resolution quantitative Schlieren imaging technique thus serves as a valuable tool for exploring complex fluid dynamics and supporting advancements in laser-plasma physics research.