Recursos de colección
Caltech Authors (143.226 recursos)
Repository of works by Caltech published authors.
Group = Moore Center for Theoretical Cosmology and Physics
Repository of works by Caltech published authors.
Group = Moore Center for Theoretical Cosmology and Physics
Bao, Ning; Remmen, Grant N.
We prove, for any state in a conformal field theory defined on a set of
boundary manifolds with corresponding classical holographic bulk geometry, that
for any bipartition of the boundary into two non-clopen sets, the density
matrix cannot be a direct product of the reduced density matrices on each
region of the bipartition. In particular, there must be entanglement across the
bipartition surface. We extend this no-go theorem to general, arbitrary
partitions of the boundary manifolds into non-clopen parts, proving that the
density matrix cannot be a direct product. This result gives a necessary
condition for states to potentially correspond to holographic duals.
Bao, Ning; Cao, ChunJun; Carroll, Sean M.; McAllister, Liam
We consider cosmological evolution from the perspective of quantum
information. We present a quantum circuit model for the expansion of a comoving
region of space, in which initially-unentangled ancilla qubits become entangled
as expansion proceeds. We apply this model to the comoving region that now
coincides with our Hubble volume, taking the number of entangled degrees of
freedom in this region to be proportional to the de Sitter entropy. The quantum
circuit model is applicable for at most 140 e-folds of inflationary and
post-inflationary expansion: we argue that no geometric description was
possible before the time t_1 when our comoving region was one Planck length
across, and contained one...
Carroll, Sean M.
Some modern cosmological models predict the appearance of Boltzmann Brains:
observers who randomly fluctuate out of a thermal bath rather than naturally
evolving from a low-entropy Big Bang. A theory in which most observers are of
the Boltzmann Brain type is generally thought to be unacceptable, although
opinions differ. I argue that such theories are indeed unacceptable: the real
problem is with fluctuations into observers who are locally identical to
ordinary observers, and their existence cannot be swept under the rug by a
choice of probability distributions over observers. The issue is not that the
existence of such observers is ruled out by data, but that the theories...
Cao, ChunJun; Zhitnitsky, Ariel R.
We propose a new table-top experimental configuration for the direct detection
of dark matter axions with mass in the (10^(−6) eV − 10^(−2)eV) range using non-perturbative
effects in a system with non-trivial spatial topology. Different from most experimental
setups found in literature on direct dark matter axion detection, which relies on ˙θ or ∇~ θ,
we found that our system is in principle sensitive to a static θ ≥ 10^(−14) and can also be used
to set limit on the fundamental constant θ_(QED) which becomes the fundamental observable
parameter of the Maxwell system if some conditions are met. Connection with Witten
effect when the induced electric charge...
Bao, Ning; Bouland, Adam; Chatwin-Davies, Aidan; Pollack, Jason; Yuen, Henry
The AMPS paradox challenges black hole complementarity by apparently constructing a way for an observer to bring information from the outside of the black hole into its interior if there is no drama at its horizon, making manifest a violation of monogamy of entanglement. We propose a new resolution to the paradox: this violation cannot be explicitly checked by an infalling observer in the finite proper time they have to live after crossing the horizon. Our resolution depends on a weak relaxation of the no-drama condition (we call it “little-drama”) which is the “complementarity dual” of scrambling of information on...
Kim, Ji-hoon; Hopkins, Philip F.; Hummels, Cameron B.
Using an isolated Milky Way-mass galaxy simulation, we compare results from nine state-of-the-art gravito-hydrodynamics codes widely used in the numerical community. We utilize the infrastructure we have built for the AGORA High-resolution Galaxy Simulations Comparison Project. This includes the common disk initial conditions, common physics models (e.g., radiative cooling and UV background by the standardized package Grackle) and common analysis toolkit yt, all of which are publicly available. Subgrid physics models such as Jeans pressure floor, star formation, supernova feedback energy, and metal production are carefully constrained across code platforms. With numerical accuracy that resolves the disk scale height, we...
Ma, Xiangcheng; Hopkins, Philip F.; Wetzel, Andrew R.; Kirby, Evan N.; Anglés-Alcázar, Daniel; Faucher-Giguère, Claude-André; Kereš, Dušan; Quataert, Eliot
We study the structure, age and metallicity gradients, and dynamical evolution using a cosmological zoom-in simulation of a Milky Way-mass galaxy from the Feedback in Realistic Environments project. In the simulation, stars older than 6 Gyr were formed in a chaotic, bursty
mode and have the largest vertical scale heights (1.5–2.5 kpc) by z = 0, while stars younger than 6 Gyr were formed in a relatively calm, stable disk. The vertical scale height increases with stellar age at all radii, because (1) stars that formed earlier were thicker ‘at birth’, and (2) stars were kinematically heated to an even thicker...
Bao, N.; Chatwin-Davies, A.
We present a constructive algorithm for the determination of Ryu-Takayanagi surfaces in AdS_3/CFT_2 which exploits previously noted connections between holographic entanglement entropy and max-flow/min-cut. We then characterize its complexity as a polynomial time algorithm.
Lu, Yu; Benson, Andrew; Mao, Yao-Yuan; Tonnesen, Stephanie; Peter, Annika H. G.; Wetzel, Andrew R.; Boylan-Kolchin, Michael; Wechsler, Risa H.
Many properties of the Milky Way's (MW) dark matter halo, including its mass-assembly history, concentration, and subhalo population, remain poorly constrained. We explore the connection between these properties of the MW and its satellite galaxy population, especially the implication of the presence of the Magellanic Clouds for the properties of the MW halo. Using a suite of high-resolution N-body simulations of MW-mass halos with a fixed final M_(vir) ~ 10^(12.1),M_⊙, we find that the presence of Magellanic Cloud-like satellites strongly correlates with the assembly history, concentration, and subhalo population of the host halo, such that MW-mass systems with Magellanic Clouds...
Wetzel, Andrew R.; Hopkins, Philip F.; Kim, Ji-Hoon; Faucher-Giguère, Claude-André; Kereš, Dušan; Quataert, Eliot
Low-mass "dwarf" galaxies represent the most significant challenges to the cold dark matter (CDM) model of cosmological structure formation. Because these faint galaxies are (best) observed within the Local Group (LG) of the Milky Way (MW) and Andromeda (M31), understanding their formation in such an environment is critical. We present first results from the Latte Project: the Milky Way on Feedback in Realistic Environments (FIRE). This simulation models the formation of an MW-mass galaxy to z = 0 within ΛCDM cosmology, including dark matter, gas, and stars at unprecedented resolution: baryon particle mass of 7070 M_⊙ with gas kernel/softening that...
Ridgway, Alexander K.; Wise, Mark B.
We discuss the physical interpretation of stress-energy tensors that source static spherically symmetric Kerr-Schild metrics. We find that the sources of such metrics with no curvature singularities or horizons do not simultaneously satisfy the weak and strong energy conditions. Sensible stress-energy tensors usually satisfy both of them. Under most circumstances, these sources are not perfect fluids and contain shear stresses. We show that for these systems the classical double copy associates the electric charge density to the Komar energy density. In addition, we demonstrate that the stress-energy tensors are determined by the electric charge density and their conservation equations.
Cao, ChunJun; Carroll, Sean M.; Michalakis, Spyridon
We examine how to construct a spatial manifold and its geometry from the entanglement structure of an abstract quantum state in Hilbert space. Given a decomposition of Hilbert space H into a tensor product of factors, we consider a class of “redundancy-constrained states” in H that generalize the area-law behavior for entanglement entropy usually found in condensed-matter systems with gapped local Hamiltonians. Using mutual information to define a distance measure on the graph, we employ classical multidimensional scaling to extract the best-fit spatial dimensionality of the emergent geometry. We then show that entanglement perturbations on such emergent geometries naturally give...
Remmen, Grant N.; Bao, Ning; Pollack, Jason
We consider the question of entanglement conservation in the context of the ER=EPR correspondence equating quantum entanglement with wormholes. In quantum mechanics, the entanglement between a system and its complement is conserved under unitary operations that act independently on each; ER=EPR suggests that an analogous statement should hold for wormholes. We accordingly prove a new area theorem in general relativity: for a collection of dynamical wormholes and black holes in a spacetime satisfying the null curvature condition, the maximin area for a subset of the horizons (giving the largest area attained by the minimal cross section of the multi-wormhole throat...
An, Haipeng; Wise, Mark B.; Zhang, Yue
We consider a dark sector consisting of dark matter that is a Dirac fermion and a scalar mediator. This model has been extensively studied in the past. If the scalar couples to the dark matter in a parity conserving manner then dark matter annihilation to two mediators is dominated by the P-wave channel and hence is suppressed at very low momentum. The indirect detection constraint from the anisotropy of the Cosmic Microwave Background is usually thought to be absent in the model because of this suppression. In this letter we show that dark matter annihilation to bound states occurs through...
El-Badry, Kareem; Wetzel, Andrew; Geha, Marla; Hopkins, Philip F.; Kereš, Dusan; Chan, T. K.; Faucher-Giguère, Claude-André
We examine the effects of stellar feedback and bursty star formation on low-mass galaxies (M_(star) = 2 × 10^6 − 5 × 10^(10) M_⊙) using the Feedback in Realistic Environments (FIRE) simulations. While previous studies emphasized the impact of feedback on dark matter profiles, we investigate the impact on the stellar component: kinematics, radial migration, size evolution, and population gradients. Feedback-driven outflows/inflows drive significant radial stellar migration over both short and long timescales via two processes: (1) outflowing/infalling gas can remain star-forming, producing young stars that migrate ~1 kpc within their first 100 Myr, and (2) gas outflows/inflows drive strong...
Nakayama, Yu; Ooguri, Hirosi
In a weakly coupled gravity theory in the anti-de Sitter space, local states in the bulk are linear superpositions of Ishibashi states for a crosscap in the dual conformal field theory. The superposition structure can be constrained either by the microscopic causality in the bulk gravity or the bootstrap condition in the boundary conformal field theory. We show, contrary to some expectation, that these two conditions are not compatible to each other in the weak gravity regime. We also present an evidence to show that bulk local states in three dimensions are not organized by the Virasoro symmetry.
Cao, ChunJun; Yao, Yuan; Zhitnitsky, Ariel R.
We study novel types of contributions to the partition function of the Maxwell system defined on a small compact manifold. These contributions, often not addressed in the perturbative treatment with physical photons, emerge as a result of tunneling transitions between topologically distinct but physically identical vacuum winding states. These new terms give an extra contribution to the Casimir pressure, yet to be measured. We argue that this effect is highly sensitive to a small external electric field, which should be contrasted with the conventional Casimir effect, where the vacuum photons are essentially unaffected by any external field. Furthermore, photons will...
An, Haipeng; Wise, Mark B.; Zhang, Yue
We study the impact of bound state formation on dark matter annihilation rates in models where dark matter interacts via a light mediator, the dark photon. We derive the general cross section for radiative capture into all possible bound states, and point out its nontrivial dependence on the dark matter velocity and the dark photon mass. For indirect detection, our result shows that dark matter annihilation inside bound states can play an important role in enhancing signal rates over the rate for direct dark matter annihilation with Sommerfeld enhancement. The effects are strongest for large dark gauge coupling and when...
Hopkins, Philip F.
We extend recently-developed mesh-free Lagrangian methods for numerical
magnetohydrodynamics (MHD) to arbitrary anisotropic diffusion equations,
including: passive scalar diffusion, Spitzer-Braginskii conduction and
viscosity, cosmic ray diffusion/streaming, anisotropic radiation transport,
non-ideal MHD (Ohmic resistivity, ambipolar diffusion, the Hall effect), and
turbulent 'eddy diffusion.' We study these as implemented in the code GIZMO for
both new meshless finite-volume Godunov schemes (MFM/MFV) as well as
smoothed-particle hydrodynamics (SPH). We show the MFM/MFV methods are accurate
and stable even with noisy fields and irregular particle arrangements, and
recover the correct behavior even in arbitrarily anisotropic cases. They are
competitive with state-of-the-art AMR/moving-mesh methods, and can correctly
treat anisotropic diffusion-driven instabilities (e.g. the MTI and HBI,...
Dixon, Lance J.; Esterlis, Ilya
Loop-level scattering amplitudes for massless particles have singularities in regions where tree amplitudes are perfectly smooth. For example, a 2 → 4 gluon scattering process has a singularity in which each incoming gluon splits into a pair of gluons, followed by a pair of 2 → 2 collisions between the gluon pairs. This singularity mimics double parton scattering because it occurs when the transverse momentum of a pair of outgoing gluons vanishes. The singularity is logarithmic at fixed order in perturbation theory. We exploit the duality between scattering amplitudes and polygonal Wilson loops to study six-point amplitudes in this limit...