arXiv subjects

Ashik H

Publications and source records attributed to Ashik H.

3 recordsLinked to original sources

arXiv2026

Mapping Tachyon effective field theory to a subsector of Klein-Gordon theory

On an unstable D-brane, the rolling of the tachyon away from the maximum of its potential is described by time-dependent solutions in string theory. Subsequent analysis leads to an understanding of physics around the tachyon vacuum in terms of an effective field theory. The classical solutions of this effective field theory in the late time limit are in one-to-one correspondence with configurations of non-rotating, non-interacting dust particles. In this work, we map this effective theory near the minimum of the potential to a consistent quantum description using collective field theory methods. The Hilbert space description we obtain in this way consists of a coherent state of particles at rest and excitations on top, i.e., a subsector of Klein-Gordon theory. This is in accordance with known results where one considers a decaying D-brane as providing a time-dependent source for closed strings, and the final closed string state produced is a coherent state. It also suggests, at the quantum level, an equivalence between the open string description and the closed string description regarding the decay of an unstable D-brane.

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arXiv2025

Cosmological correlators in gravitationally-constrained de Sitter states

We study cosmological correlators in de Sitter quantum gravity in the limit where $G_N \to 0$. This limit is distinct from a nongravitational QFT because the gravitational constraints still force states and observables to be de Sitter invariant. We first examine a class of perturbative correlators that, in gauge-fixed form, are represented by the expectation value of a product of elementary fields on the late-time boundary. We formulate Feynman rules for our computations and enumerate some necessary, but not sufficient, conditions that must be imposed on states and operators to avoid group-volume divergences. These correlators are conformally invariant in all allowed perturbative states but never coincide with QFT vacuum-expectation values. For instance, our sample computations yield interesting non-Gaussianities even when the underlying vacuum wavefunction is Gaussian. However, we show that, in the presence of a heavy background state, it is possible to construct a separate class of state-dependent relational observables whose values approximate QFT correlators in the vacuum. This illustrates a key contrast in quantum gravity -- between observables that are microscopically simple and observables whose expectation values in an appropriate background state lead to simple QFT-like correlators.

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arXiv2024

Holography of Information in a Ball of Finite Radius

The principle of holography of information states that all information available in the bulk of asymptotically flat spacetime is also available near its boundary at spatial infinity. However, physical observers never have access to spatial infinity. Therefore, we ask the question: ``Is information contained in a ball of finite radius also holographic in nature?". Phrased differently, we ask whether correlation functions on the boundary of the ball capture all the information of all correlators in the bulk of the ball. In this work, we answer this question in the affirmative within the confines of linearised quantum gravity for generic low-energy (free Klein-Gordon) states in flat space created by the action of unitaries on the vacuum to leading order in a certain perturbative parameter. For an infinite sub-class of these states, our results are perturbatively exact and valid to all orders in this same parameter. Unlike at infinity, massive and massless fields can be captured within the same framework.

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