arXiv subjects

Achintya Sajeendran

Publications and source records attributed to Achintya Sajeendran.

3 recordsLinked to original sources

arXiv2026

Time-energy uncertainty relation from subcycle mode vacuum fluctuations of a quantum field

The time-energy uncertainty relation is often invoked as a heuristic explanation for virtual particles in interacting quantum field theories. However, this interpretation breaks down upon closer scrutiny for several reasons, particularly since virtual particles do not have a well-defined temporal extension. Although concrete derivations and interpretations of time-energy uncertainty bounds in quantum mechanics have been established, most famously by Mandelstam and Tamm in 1945, there is no known rigorous connection between these bounds and the concept of virtual particles in quantum field theory. In this work, we use a model in which the vacuum particle content associated with subcycle, spatiotemporally localised modes of a free scalar field can be converted into excitations of a rapidly-switched harmonic-oscillator Unruh-DeWitt detector coupled to the conjugate field. Defining the time uncertainty as the effective duration of the detector-field interaction and identifying the contribution to the energy fluctuations of the detector resulting from the subcycle mode vacuum fluctuations, we show that a time-energy uncertainty relation is satisfied in the deep subcycle regime. Our results provide a concrete operational meaning to the textbook heuristic picture of virtual particles in quantum field theory in terms of the time-energy uncertainty principle.

quant-ph↗

arXiv2026

Quantum coherent dynamics of quasiclassical spacetimes

In a wide range of quantum gravity theories, quasiclassical geometries, which are solutions to the Einstein field equations approximately, are described by "coherent states." Here we propose a Hamiltonian formalism for gravitational dynamics with respect to this coherent state basis, which generates time evolution of the spacetime with respect to a clock at infinity. Since the coherent states are not orthogonal, an initial quasiclassical geometry is dynamically driven into a superposition of different amplitudes. Our framework provides a dynamical mechanism for tunneling between geometries that is ubiquitous in a number of approaches to quantum gravity, from loop quantum gravity to the Euclidean path integral. We apply our framework to the problem of black hole evaporation, providing a hint at how unitarity may be preserved with the inclusion of quantum corrections to the semiclassical evolution of the black hole.

gr-qc↗

arXiv2025

Looping back to the past through free fall in a controlled warp drive spacetime

We present a modification to a 'rotating' version of the dynamical Alcubierre spacetime, which was previously shown to permit closed timelike curves. We find that if the effective rotation rate is made dependent on the spacetime coordinates within the bubble, a class of closed timelike curves are promoted to spatially circular geodesics. These paths provide a simple model of a free particle interacting with a CTC for a finite proper time interval, entering and exiting in flat spacetime. Despite the questionable physical realisability of our metric, we suggest that it may provide a useful background for future theoretical studies of classical and quantum models of time travel in a general relativistic setting.

gr-qc↗