Raman Research Institute (RRI) is an institute of scientific research located in Bangalore, India. It was founded by Nobel laureate C. V. Raman. Although it began as an institute privately owned by Sir C. V. Raman, it is now funded by the government of India.
We study a non-reciprocal version of Model B, as the continuum theory for non-reciprocal particle mixtures. In contrast to non-reciprocal Cahn-Hilliard models, it is important in this context to consider the dependence of mobility coefficients on the local concentrations. We show that a homogeneous state that is linearly stable for one form of the mobility can be unstable for a different form of mobility, an effect that would be impossible in equilibrium and implies a crucial role for mobilities in non-reciprocal mixtures. For unstable homogeneous states we study the spinodal dynamics governing the onset of phase separation. We find, again in contrast to non-reciprocal Cahn-Hilliard models, that exceptional point transitions between static and oscillatory instabilities are generically avoided by first order transitions where the spinodal lengthscale changes discontinuously. At these transitions we find intricate spinodal dynamics with two competing lengthscales, one governing a static instability and the other an oscillatory instability, i.e. one that generates travelling waves. We demonstrate that, depending on interaction strengths, more complex transitions can occur in the spinodal dynamics, including coexistence of three lengthscales and first order transition lines, terminated by critical points, between distinct static instabilities. Finally, we explore the effects of additional non-reciprocity in the interfacial chemical potentials, which would generically be expected when obtaining Model B by coarse graining from a non-reciprocal particle model. We show that interfacial non-reciprocity can increase the region in the spinodal phase diagram where oscillatory instabilities occur, but only up to a certain boundary that we establish analytically and demonstrate numerically.
We introduce proxitaxis, a simple search strategy where the searcher has only information about the distance from the target but not the direction. The strategy consists of three crucial components: (i) local adaptive moves with a distance-dependent diffusion coefficient, (ii) intermittent long-range returns via stochastic resetting to a certain location R[over ⃗]_{0}, and (iii) an inspection move where the searcher dynamically updates the resetting position R[over ⃗]_{0}. We compute analytically the capture probability of the target within this strategy and show that it can be maximized by an optimal choice of the control parameters of this strategy. Moreover, the optimal strategy undergoes multiple phase transitions as a function of the control parameters. These phase transitions are generic and occur in all dimensions.
Building upon our recently established correspondence between quantum cosmology and the hydrogen atom (Sahota et al 2025 arXiv:2505.16863 [gr-qc]), we investigate the specific sector of a negative cosmological constant ( Lambda<0) in a flat FLRW Universe with dust. While the positive Lambda sector (Sahota et al 2025 arXiv:2505.16863 [gr-qc]) yields a continuous spectrum and a single bounce, we show here that the negative Lambda sector leads to a discrete spectrum of energy eigenvalues, effectively quantizing the cosmological constant. Within this dual description, the operator-ordering ambiguity parameter appears as the azimuthal quantum number of the hydrogen atom. A skewed Bohr correspondence emerges for the bound states, matching classical evolution at large volumes but deviating near the bounce. By constructing wave packets from these bound states, we demonstrate that the classical Big Bang and Big Crunch singularities are resolved, and the Universe oscillates between quantum bounces and classical turnaround points. The expectation values of the observables indicate a cyclic Universe-with vanishing Hubble parameter at turnarounds-undergoing quantum bounces. This exactly solvable model offers a tractable setting to explore quantum gravitational effects in cosmology. We analyze the properties of this cyclic Universe, contrasting its bound-state dynamics with the scattering states of the de Sitter case.
Abstract We analyze the Wheeler-DeWitt quantization of a spatially flat Friedmann–Lemaïtre–Robertson–Walker universe containing pressureless dust and a positive cosmological constant ( $$\Lambda > 0$$ Λ > 0 ). Following relational time framework, we establish a direct mathematical correspondence between the cosmological Hamiltonian and the radial Schrödinger equation for the scattering states of the non-relativistic hydrogen atom. This exact solvability allows us to rigorously construct the physical Hilbert space and ensure the self-adjointness of the Hamiltonian. As a concrete result, we show that the wave packets unitarily evolve depicting a non-singular quantum bounce, systematically replacing the classical Big Bang singularity. Finally, we discuss the physical relevance of this exact solution within the matter-bounce scenario. We demonstrate that this framework provides a robust quantum origin for a bounce during a dust-dominated contracting phase—a necessary prerequisite for generating a scale-invariant spectrum of primordial perturbations—derived from the unitary dynamics of the quantized background.
The highest-energy cosmic neutrino detected by the ARCA detector of KM3NeT has reignited the quest to pinpoint the sources of ultrahigh-energy cosmic rays (UHECRs; E ≳ 0.1 EeV). By uncovering the associated multimessenger signals, we investigate the origin of the 220 PeV ν _μ event KM3-230213A from an unknown transient that accelerated cosmic rays to ∼10 EeV. Unlike an astrophysical origin, where the ν _μ is produced inside the source, here we consider UHECR protons that escape the source interact with the cosmic background radiation, producing a PeV–EeV cosmogenic neutrino spectrum. The secondary e ^± and γ -rays initiate an electromagnetic cascade, resulting in a cosmogenic γ -ray spectrum. The latter peaks at a delayed time of ≳10 ^4 yr compared to the light travel time from the transient to observer, due to deflection of charged particles in the extragalactic magnetic field (EGMF). Our results shed light on the nature of the UHECR source for the ν _μ event and provide crucial insights into the detection of multi-TeV γ -rays of cosmogenic origin from similar past cosmological transients. Using the γ -ray sensitivity of currently operating and next-generation imaging atmospheric Cherenkov telescopes, the flux and time-delay distribution can constrain the source distance. We further show that the detection of such a γ -ray signal above the background depends on the EGMF strength. Together with the nondetection of coincident spatial or temporal photon counterparts at the current epoch, this detection is the first compelling candidate for a sub-EeV cosmogenic neutrino.
