Naive Expectation Research Articles

Thermalization and hotspot formation around small primordial black holes

We quantitatively analyze a basic question: what is the stationary solution of the background plasma temperature profile around a black hole (BH)? One may naively expect that the temperature profile continuously decreases from the Hawking temperature at the surface of the BH towards an outer region. We show analytically and numerically that this is not the case because local thermal equilibrium cannot be maintained near the surface of the BH and also because the high-energy particles emitted from Hawking radiation cannot be instantaneously thermalized into the background plasma. The temperature profile has a plateau within a finite distance from the BH, and even the overall amplitude of background temperature at a distance far away from the BH is significantly suppressed compared with the naive expectation. The main reason for these counterintuitive results comes from the fact that the size of the BH is too small that particles of Hawking radiation goes far away within the typical time scale of interactions.

Local clustering of relic neutrinos: comparison of kinetic field theory and the Vlasov equation

Gravitational clustering in our cosmic vicinity is expected to lead to an enhancement of the local density of relic neutrinos. We derive expressions for the neutrino density, using a perturbative approach to kinetic field theory and perturbative solutions of the Vlasov equation up to second order. Our work reveals that both formalisms give exactly the same results and can thus be considered equivalent. Numerical evaluation of the local relic neutrino density at first and second order provides some fundamental insights into the frequently applied approach of linear response to neutrino clustering (also known as the Gilbert equation). Against the naive expectation, including the second-order contribution does not lead to an improvement of the prediction for the local relic neutrino density but to a dramatic overestimation. This is because perturbation theory breaks down in a momentum-dependent fashion and in particular for densities well below unity.

Subsystem complexity and measurements in holography

We investigate the impact of measuring one subsystem on the holographic complexity of another. While a naive expectation might suggest a reduction in complexity due to the collapse of the state to a trivial product state during quantum measurements, our findings reveal a counterintuitive result: in numerous scenarios, measurements on one subsystem can amplify the complexity of another. We first present a counting argument elucidating this complexity transition in random states. Then, employing the subregion “complexity=volume” (CV) proposal, we identify a complexity phase transition induced by projective measurements in various holographic CFT setups, including CFT vacuum states, thermofield double states, and the joint system of a black hole coupled to a bath. According to the AdS/BCFT correspondence, the post-measurement dual geometry involves an end-of-the-world brane created by the projective measurement. The complexity phase transition corresponds to the transition of the entanglement wedge to the one connected to the brane. In the context of the thermofield double setup, complete projection on one side can transform the other side into a boundary state black hole with higher complexity or a pure AdS with lower complexity. In the joint system of a black hole coupled to a nongraviting bath, where (a part of) the radiation is measured, the BCFT features two boundaries: one for the black hole and the other for the measurement. We construct the bulk dual involving intersecting or non-intersecting branes, and investigate the complexity transition induced by the projective measurement. Notably, for a subsystem that contains the black hole brane, its RT surface may undergo a transition, giving rise to a complexity jump.

Non-linearities in cosmological bubble wall dynamics

A precise modelling of the dynamics of bubbles nucleated during first-order phase transitions in the early Universe is pivotal for a quantitative determination of various cosmic relics, including the stochastic background of gravitational waves. The equation of motion of the bubble front is affected by the out-of-equilibrium distributions of particle species in the plasma which, in turn, are described by the corresponding Boltzmann equations. In this work we provide a solution to these equations by thoroughly incorporating the non-linearities arising from the population factors. Moreover, our methodology relies on a spectral decomposition that leverages the rotational properties of the collision integral within the Boltzmann equations. This novel approach allows for an efficient and robust computation of both the bubble speed and profile. We also refine our analysis by including the contributions from the electroweak gauge bosons. We find that their impact is dominated by the infrared modes and proves to be non-negligible, contrary to the naive expectations.

Accidentally light scalars from large representations

In models with spontaneous symmetry breaking by scalar fields in large group representations, we observe that some of the scalar masses can be loop-suppressed with respect to the naive expectation from symmetry selection rules. We present minimal models — the SU(2) five-plet and SU(3) ten-plet — with such accidentally light scalars, featuring compact tree-level flat directions lifted by radiative corrections. We sketch some potential applications, from stable relics and slow roll in cosmology, to hierarchy and fine-tuning problems in particle physics.

Instanton effects in twist-3 generalized parton distributions

The instanton vacuum picture is used to study hadronic matrix elements of the twist-3 (dimension-4, spin-1) QCD operators measuring the quark spin density and spin-orbit correlations. The QCD operators are converted to effective operators in the low-energy effective theory emerging after chiral symmetry breaking, in a systematic approach based on the diluteness of the instanton medium and the 1/Nc expansion. The instanton fields induce spin-flavor-dependent “potential” terms in the effective operators, complementing the “kinetic” terms from the quark field momenta. As a result, the effective operators obey the same equation-of-motion relations as the original QCD operators. The spin-orbit correlations are qualitatively different from naive quark model expectations.

No end in sight: Mysteries of the telomeric variation in plants.

One of the most fascinating phenomena in evolutionary biology is the rapid evolution of genes with conserved functions across the tree of life. Because the cellular and organismal development processes are highly conserved across eukaryotes, a naive evolutionary expectation is that the genes involved in those processes would also be under high selective constraint and evolve extremely slowly. However, we now know that evolutionarily young genes can rapidly acquire crucial viability functions and even evolutionarily old genes can have unexpected levels of rapid evolution within specific lineages (Talbert et al. 2004). These studies have led to novel insights of function and evolution in molecular systems that are universally important for almost all organisms. This article is protected by copyright. All rights reserved.

Why does history surprise us?

The Russian military aggression against Ukraine in February 2022 unveiled the illusory nature of our faith in the stability of the global political system. This belief was largely rooted in our short-term observations and naive expectations that political structures and social relationships were fixed points in the evolution of history. However, the reality is that we cannot assume the socio-political order we know to be the sole possible state, nor should we expect the transition to new solutions to occur smoothly. This study presents three agent-based models demonstrating how changes in socio-political structures can exhibit a discontinuous nature. These models include a social impact model with a strong leader, a model of interactions among competing social groups, and a model of structural balance dynamics. The discontinuous changes observed stem from the multistability of multiagent models, and the resulting transitions are both irreversible and exhibit hysteresis behaviour. All the transitions considered correspond to tipping points and the critical parameter values calculated through analytical approaches agree with the results of agent-based numerical simulations. The outcomes of these models exhibit qualitative agreement with historical data, particularly concerning the causes of the First World War and Adolf Hitler’s ascent to absolute power in Germany, while also complementing observed variations in connection density within echo chambers formed by conservative and liberal communities in U.S.

Exact analytical solution of the one-dimensional time-dependent radiative transfer equation with linear scattering

The radiative transfer equation (RTE) is a cornerstone for describing the propagation of electromagnetic radiation in a medium, with applications spanning atmospheric science, astrophysics, remote sensing, and biomedical optics. Despite its importance, an exact analytical solution to the RTE has remained elusive, necessitating the use of numerical approximations such as Monte Carlo, discrete ordinate, and spherical harmonics methods. In this paper, we present an exact solution to the one-dimensional time-dependent RTE. We delve into the moments of the photon distribution, providing a clear view of the transition to the diffusion regime. This analysis offers a deeper understanding of light propagation in the medium. Furthermore, we demonstrate that the one-dimensional RTE is equivalent to the Klein-Gordon equation with an imaginary mass term determined by the inverse reduced scattering length. Contrary to naive expectations of superluminal solutions, we find that our solution is strictly causal under appropriate boundary conditions, determined by the light transport problem. We validate the found solution using Monte Carlo simulations and benchmark the performance of the latter. Our analysis reveals that even for highly forward scattering, dozens of random light scatterings are required for an accurate estimate, underscoring the complexity of the problem. Moreover, we propose a method for faster convergence by adjusting the parameters of Monte Carlo sampling. We show that a Monte Carlo method sampling photon scatterings with input parameters (μs,g), where μs is the inverse scattering length and g is the scattering anisotropy parameter, is equivalent to that with (μs(1−g)/2,−1). This equivalence leads to a significantly faster convergence to the exact solution, offering a substantial improvement of the Monte Carlo method for the one-dimensional RTE. Our findings not only contribute to the theoretical understanding of the RTE but also have potential implications for improving the numerical methods used to approximate it.

Comparative Performance of Computer Simulation Models of Intrinsically Disordered Proteins at Different Levels of Coarse-Graining.

Coarse-graining is commonly used to decrease the computational cost of simulations. However, coarse-grained models are also considered to have lower transferability, with lower accuracy for systems outside the original scope of parametrization. Here, we benchmark a bead-necklace model and a modified Martini 2 model, both coarse-grained models, for a set of intrinsically disordered proteins, with the different models having different degrees of coarse-graining. The SOP-IDP model has earlier been used for this set of proteins; thus, those results are included in this study to compare how models with different levels of coarse-graining compare. The sometimes naive expectation of the least coarse-grained model performing best does not hold true for the experimental pool of proteins used here. Instead, it showed the least good agreement, indicating that one should not necessarily trust the otherwise intuitive notion of a more advanced model inherently being better in model choice.

Electronic origin of ferroic quadrupole moment under antiferroic quadrupole order and finite magnetic moment in Jeff=32 systems

We study the electronic origin of parasitic ferroic quadrupole moments in antiferroic quadrupole orders by extending a model studied in G. Chen et al., Phys. Rev. B 82, 174440 (2010) with the effective angular momentum ${J}_{\mathrm{eff}}=3/2$ quartet ground states. Taking into account the first crystalline-electric-field (CEF) excited doublet, cubic anisotropy in the quadrupole moments emerges, which leads to the induced ferroic quadrupole moments in the antiferroic quadrupolar phases. The hybridization with the CEF excited quartet states also causes finite magnetic moments compatible to the observed size of the effective moment in typical ${J}_{\mathrm{eff}}=3/2$ systems, as opposed to the naive expectation of vanishing moments in the ${J}_{\mathrm{eff}}=3/2$ systems. These results suggest the importance of the corrections arising from the high-energy CEF excited states in the ${J}_{\mathrm{eff}}=3/2$ systems.

Conditions for Graviton Emission in the Recombination of a Delocalized Mass

In a known gedanken experiment, a delocalized mass is recombined while the gravitational field sourced by it is probed by another (distant) particle; in it, this is used to explore a possible tension between complementarity and causality in case the gravitational field entangles with the superposed locations, a proposed resolution being graviton emission from quadrupole moments. Here, we focus on the delocalized particle (forgetting about the probe and the gedanken experiment) and explore the conditions (in terms of mass, separation, and recombination time) for graviton emission. Through this, we find that the variations of quadrupole moments in the recombination are generically greatly enhanced if the field is entangled compared to if it is sourced instead by the energy momentum expectation value on the delocalized state (moment variation ∼md2 in the latter case, with m mass, d separation). In addition, we obtain the (upper) limit recombination time for graviton emission growing as m in place of the naive expectation m. In this, the Planck mass acts as threshold mass (huge, for delocalized objects): no graviton emission is possible below it, however fast the recombination occurs. If this is compared with the decay times foreseen in the collapse models of Diósi and Penrose (in their basic form), one finds that no (quadrupole) graviton emission from recombination is possible in them. Indeed, right when m becomes large enough to allow for emission, it also becomes too large for the superposition to survive collapse long enough to recombine.

Eigenvalue analysis of stress-strain curve of two-dimensional amorphous solids of dispersed frictional grains with finite shear strain.

The stress-strain curve of two-dimensional frictional dispersed grains interacting with a harmonic potential without considering the dynamical slip under a finite strain is determined by using eigenvalue analysis of the Hessian matrix. After the configuration of grains is obtained, the stress-strain curve based on the eigenvalue analysis is in almost perfect agreement with that obtained by the simulation, even if there are plastic deformations caused by stress avalanches. Unlike the naive expectation, the eigenvalues in our model do not indicate any precursors to the stress-drop events.

Dynamical demographic phases explain how population growth and mutation control the evolutionary impact of bottlenecks

Population bottlenecks involve steep declines in population size as well as changes to composition; they are an important aspect of contemporary evolution, and have been implicated across a wide range of taxa. However, the precise mechanisms by which such bottlenecks translate into altered evolutionary outcomes remain poorly understood. Here, we demonstrate how the fixation probabilities associated with such outcomes can depend nontrivially on the rates of post-bottleneck growth and mutation as a population recovers. Notably, increased population growth can invert naive expectations, driving fixation to attractors that are different to those from within whose basin the bottleneck constrained the population, initially, despite more rapidly suppressing the intrinsic fluctuations that are ostensibly required to switch between basins of attraction. Such behavior moreover only occurs beneath a critical threshold of mutation, which is itself a function of the rate of population growth. We explain our results in terms of statistically distinct regimes of demographic behavior, drawing parallels with the notion of nonequilibrium phase transitions. These regimes are delimited by sharp transitions in time, as a population grows, and ultimately result from a time-dependent antagonism between mutation and the stochastically induced effects of frequency-dependent birth. Recast in this context, the rates of population growth and mutation are seen to control long-term fixation probabilities by altering the duration and character of post-bottleneck dynamical demographic regimes.

Glassy Dynamics in Chiral Fluids.

Chiral active matter is enjoying a rapid increase of interest, spurred by the rich variety of asymmetries that can be attained in, e.g., the shape or self-propulsion mechanism of active particles. Though this has already led to the observance of so-called chiral crystals, active chiral glasses remain largely unexplored. Apossible reason for this could be the naive expectation that interactions dominate the glassy dynamics and the details of the active motion become increasingly less relevant. Here, we show that quite the opposite is true by studying the glassy dynamics of interacting chiral active Brownian particles. We demonstrate that when our chiral fluid is pushed to glassy conditions, it exhibits highly nontrivial dynamics, especially compared to a standard linear active fluid such as common active Brownian particles. Despite the added complexity, we are still able to present a full rationalization for all identified dynamical regimes. Most notably, we introduce a new "hammering" mechanism, unique to rapidly spinning particles in high-density conditions, that can fluidize a chiral active solid.

U -spin puzzle in B decays

We impose $U$-spin symmetry [$SU(2{)}_{\text{Uspin}}$] on the Hamiltonian for $B$ decays. As expected, we find the equality of amplitudes related by the exchange $d\ensuremath{\leftrightarrow}s$. We also find that the amplitudes for the $\mathrm{\ensuremath{\Delta}}S=0$ processes ${B}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$, ${B}_{s}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{K}^{\ensuremath{-}}$, and ${B}^{0}\ensuremath{\rightarrow}{K}^{+}{K}^{\ensuremath{-}}$ form a $U$-spin triangle relation. The amplitudes for ${B}_{s}^{0}\ensuremath{\rightarrow}{K}^{+}{K}^{\ensuremath{-}}$, ${B}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}{K}^{+}$, and ${B}_{s}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ form a similar $\mathrm{\ensuremath{\Delta}}S=1$ triangle relation. And these two triangles are related to one another by $d\ensuremath{\leftrightarrow}s$. We perform fits to the observables for these six decays. If perfect $U$ spin is assumed, then the fit is very poor. If $U$-spin-breaking contributions are added, then we find many scenarios that can explain the data. However, in all cases, 100% $U$-spin breaking is required, considerably larger than the naive expectation of $\ensuremath{\sim}20%$. This is the $U$-spin puzzle; it may be strongly hinting at the presence of new physics.

Manifesting hidden dynamics of a sub-component dark matter

We emphasize the distinctive cosmological dynamics in multi-component dark-matter scenarios and their impact on probing a sub-dominant component of dark matter. The dynamics originate from the conversion among different dark-matter components. We find that the temperature of the self-interacting sub-component dark matter is significantly enhanced by the dark-matter annihilation into the sub-component. The same annihilation sharply increases the required annihilation cross section for the sub-component as we consider a smaller relative abundance fraction among the dark-matter species. Because of the enhanced temperature and couplings of the sub-component, contrary to a naive expectation, the sub-component with smaller abundance fractions tends to be disfavored by dark-matter direct/indirect-detection experiments and cosmological observations. We demonstrate this by taking a dark photon portal scenario for the sub-component at the sub-GeV mass scale. For the abundance fraction ≳ 10 %, the enhanced temperature of the sub-component is subject to warm dark matter constraints which are complementary to the parameter space probed by accelerator-based experiments. Smaller abundance fractions tend to be disfavored by accelerator-based experiments due to the enhanced coupling to Standard Model particles.

Study of curling mechanism by precision kinematic measurements of curling stone’s motion

Why do curling stones curl? That is a question physicists are often asked, yet no answer has been established. Stones rotating clockwise curl right, contrary to our naive expectations. After a century of debate between contradicting hypotheses, this paper provides a possible answer based on experimental evidence. A digital image analysis technique was used to perform precision kinematic measurements of a curling stone’s motion to identify the curling mechanism. We observed a significant left–right asymmetric friction due to velocity dependence on the friction coefficient. Combined with the discrete point-like nature of the friction between ice and stone, swinging around slow-side friction points has been concluded as the dominant origin of the curling. Many new angular momentum transfer phenomena have been found, supporting this conclusion.

Effective Theory of Warped Compactifications and the Implications for KKLT

AbstractWe argue that effective actions for warped compactifications can be subtle, with large deviations in the effective potential from naive expectations owing to constraint equations from the higher‐dimensional metric. We demonstrate this deviation in a careful computation of the effective potential for the conifold deformation parameter of the Klebanov‐Strassler solution. The uncorrected naive effective potential for the conifold was previously used to argue that the Klebanov‐Strassler background would be destabilized by antibranes placed at the conifold infrared tip unless the flux was uncomfortably large. We show this result is too strong because the formerly neglected constraint equations eliminate the features of the potential that allowed for the instability in the de Sitter uplift of the KKLT scenario.

Manipulation of Majorana-Kramers qubit and its tolerance in time-reversal invariant topological superconductor

We investigate non-Abelian statistics of Majorana-Kramers pairs (MKPs) in a network system of one-dimensional time-reversal invariant topological superconductors by using numerical simulations of braiding dynamics and examine the tolerance against various perturbations which may cause decoherence of MKPs. We, first, consider effects of a magnetic field which breaks time-reversal symmetry. In contrast to a naive expectation, the non-Abelian braiding of MKPs is robust against applied magnetic fields provided that the initial and final states of a braiding process are invariant under the combination of a time reversal and a mirror reflection, even when intermediate states break the combined symmetry. Second, we investigate the stability of non-Abelian braidings in the case with gate-induced inhomogeneous potentials at junctions between superconducting nanowires, which generally generate a non-Majorana nearly zero-energy Andreeev bound state at the junctions. It is found that the non-Majorana nearly zero-energy states interfere with MKPs, resulting in the failure of non-Abelian braidings, when the length scale of the inhomogeneous potentials is comparable to the coherence length of the superconductors.