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Willy Fischler

Publications and source records attributed to Willy Fischler.

At least 37 records · Page 2Linked to original sources
arXiv2019

Holographic Purification Complexity

We study holographic subregion complexity, and its possible connection to purification complexity suggested recently by Agón et al. In particular, we study the conjecture that subregion complexity is the purification complexity by considering holographic purifications of a holographic mixed state. We argue that these include states with any amount of coarse-graining consistent with being a purification of the mixed state in question, corresponding holographically to different choices of the cutoff surface. We find that within the complexity = volume and complexity = spacetime volume conjectures, the subregion complexity is equal to the holographic purification complexity. For complexity = action, the subregion complexity seems to provide an upper bound on the holographic purification complexity, though we show cases where this bound is not saturated. One such example is provided by black holes with a large genus behind the horizon, which were studied by Fu et al. As such, one must conclude that these offending geometries are not holographic, that CA must be modified, or else that holographic subregion complexity in CA is not dual to the purification complexity of the corresponding reduced state.

hep-th↗
arXiv2018

Why The Cosmological Constant is a Boundary Condition

We review arguments that the cosmological constant (c.c.) should not be thought of as a local contribution to the energy density, but rather as an infrared boundary condition specifying particular models of quantum gravity.

hep-th↗
arXiv2018

The Gravitational Memory of a Galaxy

We argue that soft gravitational radiation leads to a misidentification of the angular momentum of stars seen in distant galaxies, and that this could be interpreted as an additional mass inside the orbit of the star. It is tempting to identify this with the modifications of Newtonian dynamics that have been claimed [1] to eliminate the necessity for dark matter. Simple estimates of the effect show that it is very small and does not have the right functional form to explain the Tully-Fisher relation. The effect does grow with the age of the universe, but if our universe is indeed dominated by a cosmological constant, then most galaxies will disappear beyond the cosmological horizon before the effect is observable. We conjecture that this effect can be thought of as a new kind of gravitational memory: a rotation of frames at infinity, relative to those near the galaxy. One of the conclusions of our work is that at very large times the linearized classical treatment of this problem is inadequate, and should be replaced by Weinberg's soft photon resummation. However, these times are so long that they do not appear relevant to the universe in which we live. Neither method of calculation leads to a significant effect on galaxy evolution.

hep-th↗
arXiv2018

Holographic complexity and non-commutative gauge theory

We study the holographic complexity of noncommutative field theories. The four-dimensional $\mathcal{N}=4$ noncommutative super Yang-Mills theory with Moyal algebra along two of the spatial directions has a well known holographic dual as a type IIB supergravity theory with a stack of D3 branes and non-trivial NS-NS B fields. We start from this example and find that the late time holographic complexity growth rate, based on the "complexity equals action" conjecture, experiences an enhancement when the non-commutativity is turned on. This enhancement saturates a new limit which is exactly 1/4 larger than the commutative value. We then attempt to give a quantum mechanics explanation of the enhancement. Finite time behavior of the complexity growth rate is also studied. Inspired by the non-trivial result, we move on to more general setup in string theory where we have a stack of D$p$ branes and also turn on the B field. Multiple noncommutative directions are considered in higher $p$ cases.

hep-th↗
arXiv2017

Robustness of Inflation to Inhomogeneous Initial Conditions

We consider the effects of inhomogeneous initial conditions in both the scalar field profile and the extrinsic curvature on different inflationary models. In particular, we compare the robustness of small field inflation to that of large field inflation, using numerical simulations with Einstein gravity in 3+1 dimensions. We find that small field inflation can fail in the presence of subdominant gradient energies, suggesting that it is much less robust to inhomogeneities than large field inflation, which withstands dominant gradient energies. However, we also show that small field inflation can be successful even if some regions of spacetime start out in the region of the potential that does not support inflation. In the large field case, we confirm previous results that inflation is robust if the inflaton occupies the inflationary part of the potential. Furthermore, we show that increasing initial scalar gradients will not form sufficiently massive inflation-ending black holes if the initial hypersurface is approximately flat. Finally, we consider the large field case with a varying extrinsic curvature K, such that some regions are initially collapsing. We find that this may again lead to local black holes, but overall the spacetime remains inflationary if the spacetime is open, which confirms previous theoretical studies.

hep-th↗
arXiv2017

Noether charge, black hole volume, and complexity

In this paper, we study the physical significance of the thermodynamic volumes of AdS black holes using the Noether charge formalism of Iyer and Wald. After applying this formalism to study the extended thermodynamics of a few examples, we discuss how the extended thermodynamics interacts with the recent complexity = action proposal of Brown et al. (CA-duality). We, in particular, discover that their proposal for the late time rate of change of complexity has a nice decomposition in terms of thermodynamic quantities reminiscent of the Smarr relation. This decomposition strongly suggests a geometric, and via CA-duality holographic, interpretation for the thermodynamic volume of an AdS black hole. We go on to discuss the role of thermodynamics in complexity = action for a number of black hole solutions, and then point out the possibility of an alternate proposal, which we dub "complexity = volume 2.0". In this alternate proposal, the complexity would be thought of as the spacetime volume of the Wheeler-DeWitt patch. Finally, we provide evidence that, in certain cases, our proposal for complexity is consistent with the Lloyd bound whereas CA-duality is not.

hep-th↗
arXiv2017

Soft Gravitons and the Flat Space Limit of Anti-deSitter Space

We argue that flat space amplitudes for the process $ 2 \to n$ gravitons at center of mass energies $\sqrt{s}$ much less than the Planck scale, will coincide approximately with amplitudes calculated from correlators of a boundary CFT for AdS space of radius $R\gg L_P$, only when $n < R/L_P$ . For larger values of $n$ in AdS space, insisting that all the incoming energy enters "the arena" [arXiv:hep-th/9901079], implies the production of black holes, whereas there is no black hole production in the flat space amplitudes. We also argue, from unitarity, that flat space amplitudes for all $n$ are necessary to reconstruct the complicated singularity at zero momentum in the $2 \to 2$ amplitude, which can therefore not be reproduced as the limit of an AdS calculation. Applying similar reasoning to amplitudes for real black hole production in flat space, we argue that unitarity of the flat space S-matrix cannot be assessed or inferred from properties of CFT correlators.

hep-th↗
arXiv2016

Physical Effects of the Gravitational $Θ$-Parameter

We describe the effect of the gravitational $Θ$-parameter on the behavior of the stretched horizon of a black hole in $(3+1)$-dimensions. The gravitational $Θ$-term is a total derivative, however, it affects the transport properties of the horizon. In particular, the horizon acquires a third order parity violating, dimensionless transport coefficient which affects the way localized perturbations scramble on the horizon. In the context of the gauge/gravity duality, the $Θ$-term induces a non-trivial contact term in the energy-momentum tensor of a $(2+1)-$dimensional large-N gauge theory, which admits a dual gravity description. As a consequence, the dual gauge theory in the presence of the $Θ$-term acquires the same third order parity violating transport coefficient.

hep-th↗
arXiv2016

Holographic Space-time Models of Anti-deSitter Space-times

We study the constraints on HST models of AdS space-time. The causal diamonds of HST along time-like geodesics of AdS space-time, fit nicely into the FRW patch of AdS space. The coordinate singularity of the FRW patch is identified with the proper time at which the Hilbert space of the causal diamond becomes infinite dimensional. For diamonds much smaller than the AdS radius, RAdS, the time dependent Hamiltonians of HST are the same as those used to describe similar diamonds in Minkowski space. In particular, they are invariant under the fuzzy analog of volume preserving diffeomorphisms of the holographic screen, which leads to fast scrambling of perturbations on the horizon of a black hole of size smaller than RAdS. We argue that, in order to take a limit of this system which converges to a CFT, one must choose Hamiltonians, in a range of proper times of order RAdS, which break this invariance, and become local in a particular choice of basis for the variables. We show that, beginning with flat, sub-RAdS, patches of dimension D, the resulting CFT, constructed from the variables of HST, is inconsistent with the entropy of large black holes, unless one has at least two compact dimensions, whose size is of order RAdS. The argument is connected to a new observation about the scrambling rate of information localized on the compact dimensions. Our construction explains why large AdS black holes do not have the fast scrambling property. Our present approach cannot deal with models where string theory is weakly coupled and RAdS is of order the string scale, because the relationship between area and entropy is non-universal in such models. On spatial length scales longer than RAdS, our mapping of HST variables into CFT shares much with the Tensor Network Renormalization Group (TNRG)[1] and is a sort of evolving error correcting code[2].

hep-th↗
arXiv2016

Membrane Paradigm, Gravitational $Θ$-Term and Gauge/Gravity Duality

Following the membrane paradigm, we explore the effect of the gravitational $Θ$-term on the behavior of the stretched horizon of a black hole in (3+1)-dimensions. We reformulate the membrane paradigm from a quantum path-integral point of view where we interpret the macroscopic properties of the horizon as effects of integrating out the region inside the horizon. The gravitational $Θ$-term is a total derivative, however, using our framework we show that this term affects the transport properties of the horizon. In particular, the horizon acquires a third order parity violating, dimensionless transport coefficient which affects the way localized perturbations scramble on the horizon. Then we consider a large-N gauge theory in (2+1)-dimensions which is dual to an asymptotically AdS background in (3+1)-dimensional spacetime to show that the $Θ$-term induces a non-trivial contact term in the energy-momentum tensor of the dual theory. As a consequence, the dual gauge theory in the presence of the $Θ$-term acquires the same third order parity violating transport coefficient.

hep-th↗
arXiv2016

Vector field instability and the primordial tensor spectrum

It has recently been shown that the presence of a spectator pseudoscalar field, coupled to photons through a Chern-Simons term, can amplify the primordial tensor spectrum without observationally disrupting the primordial scalar spectrum. The amplification occurs due to an instability that develops for the vector fields. We consider the extension of previous studies to account for the contribution arising from an inhomogeneous vector background which is generated prior to the onset of inflation. We find that there may be contributions in which net momentum is transferred between the inhomogeneous vector background and the gravitons, which would give rise to a signature different than in the absence of the semiclassical corrections. We discuss the properties the classical vector field form must have in order for these signatures to leave observable imprints, though we were unable to construct a model for generating such a vector field.

astro-ph.CO↗
arXiv2015

Hall Scrambling on Black Hole Horizons

We explore the effect of the electrodynamics $θ$-angle on the macroscopic properties of black hole horizons. Using only classical Einstein-Maxwell-Chern-Simons theory in (3+1)-dimensions, in the form of the membrane paradigm, we show that in the presence of the $θ$-term, a black hole horizon behaves as a Hall conductor, for an observer hovering outside. We study how localized perturbations created on the stretched horizon scramble on the horizon by dropping a charged particle. We show that the $θ$-angle affects the way perturbations scramble on the horizon, in particular, it introduces vortices without changing the scrambling time. This Hall scrambling of information is also expected to occur on cosmological horizons.

hep-th↗
arXiv2015

Decoupled Sectors and Wolf-Rayet Galaxies

It has recently been proposed that gamma-ray burst (GRB) events may be modified by the presence of a dark matter sector subcomponent that is charged under an unbroken U(1). This proposal depends upon there being a non-trivial density of charged dark matter in star forming regions of galaxies which host GRBs. We discuss four Wolf-Rayet galaxies (NGC 1614, NGC 3367, NGC 4216 and NGC 5430) which should contain comparable amounts of dark matter gas and visible matter gas in the star forming regions. We show that the ratio of dark jet power to visible jet power depends only on the ratio of particle mass and charge when the densities are equal, allowing for these input parameters to be probed directly by future observations of GRBs.

hep-ph↗
arXiv2015

CP Violation and Baryogenesis in the Presence of Black Holes

In a recent paper[1] Kundu and one of the present authors showed that there were transient but observable CP violating effects in the decay of classical currents on the horizon of a black hole, if the Lagrangian of the Maxwell field contained a CP violating angle θ. In this paper we demonstrate that a similar effect can be seen in the quantum mechanics of QED: a non-trivial Berry phase in the QED wave function is produced by in-falling electric charges. We also investigate whether CP violation, of this or any other type, might be used to produce the baryon asymmetry of the universe, in models where primordial black hole decay contributes to the matter content of the present universe. This can happen both in a variety of hybrid inflation models, and in the Holographic Space-time (HST) model of inflation[2].

hep-th↗
arXiv2015

Holographic Schwinger effect in de Sitter space

Using the AdS/CFT correspondence, we construct the holographic dual of a tunneling instanton describing Schwinger pair creation in de Sitter space. Our approach allows us to extract the critical value of the electric field for which the potential barrier disappears, rendering the vacuum unstable. In addition, we compute the large-$λ$, large-$N_c$ corrections to the nucleation rate and we find that it agrees with previous expectations based on perturbative computations. As a by-product of this investigation, we study the causal structure of the string dual to the nucleated pair as seen by different static observers and we show that it can be interpreted as a dynamical creation of a `gluonic' wormhole. We explain how this result provides further evidence for the ER=EPR conjecture as an equivalence between two descriptions of the same physical phenomenon.

hep-th↗
arXiv2015

Holographic Inflation Revised

This paper is a major revision of our previous work on the HST model of inflation. We identify the local fluctuations of the metric with fluctuations of the mass and angular momentum of black holes, and show that the consistency conditions in HST for a single trajectory to see more and more of a homogeneous distribution of black holes, imply that the system outside the horizon is undergoing inflation: small systems of equal entropy, are not in causal contact. Homogeneity then requires that the initial trajectory underwent inflation that expanded the black hole radius into our current horizon. The low entropy of the initial state of the universe is explained by the fact that this is the maximal entropy state, which has long lived localized excitations, and which can form structures more complex than black holes. The number of e-folds, reheat temperature of the universe and size of inflationary fluctuations are calculated in terms of a few parameters.

hep-th↗
arXiv2014

Supersymmetric Partially Interacting Dark Matter

We present a model of partially interacting dark matter (PIDM) within the framework of supersymmetry with gauge mediated symmetry breaking. Dark sector atoms are produced through Affleck-Dine baryogenesis in the dark sector while avoiding the production of Q-ball relics. We discuss the astrophysical constraints relevant for this model and the possibility of dark galactic disk formation. In addition, jet emission from rotating black holes is discussed in the context of this class of models.

hep-ph↗