Probing thermal fluctuations through scalar test particles

Abstract

The fundamental vacuum state of quantum fields, related to Minkowski space, produces divergent fluctuations that must be suppressed in order to bring reality to the description of physical systems. As a consequence, negative vacuum expectation values of classically positive-defined quantities can appear. This has been addressed in the literature as subvacuum phenomenon. Here it is investigated how a scalar charged test particle is affected by the vacuum fluctuations of a massive scalar field in D + 1 spacetime when the background evolves from empty space to a thermal bath, and also when a perfectly reflecting boundary is included. It is shown that when the particle is brought into a thermal bath it gains an amount of energy by means of positive dispersions of its velocity components. The magnitude of this effect is dependent on the temperature and also on the field mass. However, when a reflecting wall is inserted, dispersions can be positive or negative, showing that subvacuum effect happens even in a finite temperature environment. Furthermore, a remarkable result is that temperature can even improve negative velocity fluctuations. The magnitude of the residual effects depends on the switching interval of time the system takes to evolve between two states.

Anisotropic motion of a dipole in a photon gas

“…In Ref. [11] it was shown that this is so because the fluctuations of the gas of photons have anti-correlations, which, when integrated over an infinite interaction time, amount to a finite positive contribution. These anti-correlations arise because, contrarily to the usual thermal case, the field does not only push, but also pulls the dipole.…”

“…Moreover, of particular importance for the present work is the notion of subvacuum phenomena [10], for which classically positive quantities assume negative values after renormalization. It was recently shown [11] that temperature can enhance subvacuum effects in some systems of boundary physics. Yet, the possibility of detection requires the thermal fluctuations to be well-known and distinguished from the boundary contributions.…”

“…Due to the field-matter interaction, aspects of the background field can be tested through the motion of the test particle, and this induced motion resembles the modified vacuum induced motion studied in Refs. [11,[15][16][17][18][19][20]. In these works, a point-like charged particle was shown to perform a sort of random walk due to a transition between states of the electromagnetic field.…”

Quantum Brownian motion induced by an inhomogeneous tridimensional space and a $S^1\times R^3$ topological space-time

“…The stochastic motion performed by a point particle when interacting with the quantum vacuum fluctuations of a relativistic field, e.g., scalar or electromagnetic, is also known as Quantum Brownian motion (QBM). This is an example of a phenomena class which arise from quantum vacuum fluctuations and that, over the past several years, has been studied in different scenarios and with different approaches [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. The quantum vacuum fluctuations are always present but only become observable when the vacuum is somehow perturbed, for instance, by considering elements such as boundary conditions, temperature, nontrivial topology and so on.…”

“…So, negative values for the dispersions in the classical scenario does not make sense. On the other hand, in the quantum context it is possible that (∆A) 2 < 0, which can be interpreted as due to quantum uncertainty reduction [2,3], subvacuum effects [11][12][13] and failure in the renormalization process as a consequence of boundary conditions imposed on the field [10].…”