31 research outputs found
Gravity in the quantum lab
At the beginning of the previous century, Newtonian mechanics was advanced by two new revolutionary theories, Quantum Mechanics (QM) and General Relativity (GR). Both theories have transformed our view of physical phenomena, with QM accurately predicting the results of experiments taking place at small length scales, and GR correctly describing observations at larger length scales. However, despite the impressive predictive power of each theory in their respective regimes, their unification still remains unresolved. Theories and proposals for their unification exist but we are lacking experimental guidance towards the true unifying theory. Probing GR at small length scales where quantum effects become relevant is particularly problematic but recently there has been a growing interest in probing the opposite regime, QM at large scales where relativistic effects are important. This is principally because experimental techniques in quantum physics have developed rapidly in recent years with the promise of quantum technologies. Here we review recent advances in experimental and theoretical work on quantum experiments that will be able to probe relativistic effects of gravity on quantum properties. In particular, we emphasise the importance of using the framework of Quantum Field Theory in Curved Spacetime (QFTCS) in describing these experiments. For example, recent theoretical work using QFTCS has illustrated that these quantum experiments could also be used to enhance measurements of gravitational effects, such as Gravitational Waves (GWs). Verification of such enhancements, as well as other QFTCS predictions in quantum experiments, would provide the first direct validation of this limiting case of quantum gravity
General relativity as an effective field theory: The leading quantum corrections
I describe the treatment of gravity as a quantum effective field theory. This
allows a natural separation of the (known) low energy quantum effects from the
(unknown) high energy contributions. Within this framework, gravity is a well
behaved quantum field theory at ordinary energies. In studying the class of
quantum corrections at low energy, the dominant effects at large distance can
be isolated, as these are due to the propagation of the massless particles
(including gravitons) of the theory and are manifested in the
nonlocal/nonanalytic contributions to vertex functions and propagators. These
leading quantum corrections are parameter-free and represent necessary
consequences of quantum gravity. The methodology is illustrated by a
calculation of the leading quantum corrections to the gravitational interaction
of two heavy masses.Comment: 34 pages, Latex, UMHEP-40
Spherically symmetric vacuum solutions of modified gravity theory in higher dimensions
In this paper we investigate spherically symmetric vacuum solutions of
gravity in a higher dimensional spacetime. With this objective we construct a
system of non-linear differential equations, whose solutions depend on the
explicit form assumed for the function . We explicit
show that for specific classes of this function exact solutions from the field
equations are obtained; also we find approximated results for the metric tensor
for more general cases admitting close to the unity.Comment: 14 pages, no figure. New version accepted for publication in EPJ
Brownian motion in AdS/CFT
We study Brownian motion and the associated Langevin equation in AdS/CFT. The
Brownian particle is realized in the bulk spacetime as a probe fundamental
string in an asymptotically AdS black hole background, stretching between the
AdS boundary and the horizon. The modes on the string are excited by the
thermal black hole environment and consequently the string endpoint at the
boundary undergoes an erratic motion, which is identified with an external
quark in the boundary CFT exhibiting Brownian motion. Semiclassically, the
modes on the string are thermally excited due to Hawking radiation, which
translates into the random force appearing in the boundary Langevin equation,
while the friction in the Langevin equation corresponds to the excitation on
the string being absorbed by the black hole. We give a bulk proof of the
fluctuation-dissipation theorem relating the random force and friction. This
work can be regarded as a step toward understanding the quantum microphysics
underlying the fluid-gravity correspondence. We also initiate a study of the
properties of the effective membrane or stretched horizon picture of black
holes using our bulk description of Brownian motion.Comment: 54 pages (38 pages + 5 appendices), 5 figures. v2: references added,
clarifications in 6.2. v3: clarifications, version submitted to JHE
Gauge Formulation for Higher Order Gravity
This work is an application of the second order gauge theory for the Lorentz
group, where a description of the gravitational interaction is obtained which
includes derivatives of the curvature. We analyze the form of the second field
strenght, , in terms of geometrical variables. All possible
independent Lagrangians constructed with quadratic contractions of and
quadratic contractions of are analyzed. The equations of motion for a
particular Lagrangian, which is analogous to Podolsky's term of his Generalized
Electrodynamics, are calculated. The static isotropic solution in the linear
approximation was found, exhibiting the regular Newtonian behaviour at short
distances as well as a meso-large distance modification.Comment: Published versio
Branonium
We study the bound states of brane/antibrane systems by examining the motion
of a probe antibrane moving in the background fields of N source branes. The
classical system resembles the point-particle central force problem, and the
orbits can be solved by quadrature. Generically the antibrane has orbits which
are not closed on themselves. An important special case occurs for some
Dp-branes moving in three transverse dimensions, in which case the orbits may
be obtained in closed form, giving the standard conic sections but with a
nonstandard time evolution along the orbit. Somewhat surprisingly, in this case
the resulting elliptical orbits are exact solutions, and do not simply apply in
the limit of asymptotically-large separation or non-relativistic velocities.
The orbits eventually decay through the radiation of massless modes into the
bulk and onto the branes, and we estimate this decay time. Applications of
these orbits to cosmology are discussed in a companion paper.Comment: 34 pages, LaTeX, 4 figures, uses JHEP
Black Hole Entropy without Brick Walls
We present evidence which confirms a suggestion by Susskind and Uglum
regarding black hole entropy. Using a Pauli-Villars regulator, we find that 't
Hooft's approach to evaluating black hole entropy through a
statistical-mechanical counting of states for a scalar field propagating
outside the event horizon yields precisely the one-loop renormalization of the
standard Bekenstein-Hawking formula, S=\A/(4G). Our calculation also yields a
constant contribution to the black hole entropy, a contribution associated with
the one-loop renormalization of higher curvature terms in the gravitational
action.Comment: 15 pages, plain LaTex minor additions including some references;
version accepted for publicatio
Some remarks on the dynamical systems approach to fourth order gravity
Building on earlier work, we discuss a general framework for exploring the
cosmological dynamics of Higher Order Theories of Gravity. We show that once
the theory of gravity has been specified, the cosmological equations can be
written as a first-order autonomous system and we give several examples which
illustrate the utility of our method. We also discuss a number of results which
have appeared recently in the literature.Comment: 19 pages, LaTe
Interaction of Low - Energy Induced Gravity with Quantized Matter and Phase Transition Induced by Curvature
At high energy scale the only quantum effect of any asymptotic free and
asymptotically conformal invariant GUT is the trace anomaly of the
energy-momentum tensor. Anomaly generates the new degree of freedom, that is
propagating conformal factor. At lower energies conformal factor starts to
interact with scalar field because of the violation of conformal invariance. We
estimate the effect of such an interaction and find the running of the
nonminimal coupling from conformal value to . Then we discuss
the possibility of the first order phase transition induced by curvature in a
region close to the stable fixed point and calculate the induced values of
Newtonian and cosmological constants.Comment: 11 pages, LaTex, KEK-TH-397-KEK Preprint 94-3
Improved Effective Potential in Curved Spacetime and Quantum Matter - Higher Derivative Gravity Theory
\noindent{\large\bf Abstract.} We develop a general formalism to study the
renormalization group (RG) improved effective potential for renormalizable
gauge theories ---including matter--gravity--- in curved spacetime. The
result is given up to quadratic terms in curvature, and one-loop effective
potentials may be easiliy obtained from it. As an example, we consider scalar
QED, where dimensional transmutation in curved space and the phase structure of
the potential (in particular, curvature-induced phase trnasitions), are
discussed. For scalar QED with higher-derivative quantum gravity (QG), we
examine the influence of QG on dimensional transmutation and calculate QG
corrections to the scalar-to-vector mass ratio. The phase structure of the
RG-improved effective potential is also studied in this case, and the values of
the induced Newton and cosmological coupling constants at the critical point
are estimated. Stability of the running scalar coupling in the Yukawa theory
with conformally invariant higher-derivative QG, and in the Standard Model with
the same addition, is numerically analyzed. We show that, in these models, QG
tends to make the scalar sector less unstable.Comment: 23 pages, Oct 17 199