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Weak Field Limit of the Nonminimally Coupled Weyl Connection Gravity
The true nature of gravity is a remarkable open problem in Gravitation. Theoretical and observational motivations open the avenue of alternative theories of gravity. One possibility resorts to nonminimal couplings and non-metricity properties of spacetime, and is dubbed as nonminimally coupled Weyl connection gravity. It has the advantage of leading to metric field equations of second order together with a constraint equation for the Weyl vector, and has well behaved space-form. We analyse this model by exploring its weak regime and its implications for astrophysics and cosmology.
Journal Article
Gravitation from entanglement in holographic CFTs
A
bstract
Entanglement entropy obeys a ‘first law’, an exact quantum generalization of the ordinary first law of thermodynamics. In any CFT with a semiclassical holographic dual, this first law has an interpretation in the dual gravitational theory as a constraint on the spacetimes dual to CFT states. For small perturbations around the CFT vacuum state, we show that the set of such constraints for all ball-shaped spatial regions in the CFT is exactly equivalent to the requirement that the dual geometry satisfy the gravitational equations of motion, linearized about pure AdS. For theories with entanglement entropy computed by the Ryu-Takayanagi formula
S
=
/
(4
G
N
), we obtain the linearized Einstein equations. For theories in which the vacuum entanglement entropy for a ball is computed by more general Wald functionals, we obtain the linearized equations for the associated higher-curvature theories. Using the first law, we also derive the holographic dictionary for the stress tensor, given the holographic formula for entanglement entropy. This method provides a simple alternative to holographic renormalization for computing the stress tensor expectation value in arbitrary higher derivative gravitational theories.
Journal Article
Let's explore gravity
\"The earth is round, so why don't some people hang upside down? The answer is gravity! Young readers can explore the concept of gravity with vibrant, full-color photos, clear text, and critical thinking questions\"-- Provided by publisher.
Book
Effective field theory of gravity to all orders
A
bstract
We construct the general effective field theory of gravity coupled to the Standard Model of particle physics, which we name GRSMEFT. Our method allows the systematic derivation of a non-redundant set of operators of arbitrary dimension with generic field content and gravity. We explicitly determine the pure gravity EFT up to dimension ten, the EFT of a shift-symmetric scalar coupled to gravity up to dimension eight, and the operator basis for the GRSMEFT up to dimension eight. Extensions to all orders are straightforward.
Journal Article
The gravity of math : how geometry rules the universe
\"On November 25th, 1915, Albert Einstein published his field equations of general relativity and reinvented gravity. Rather than being some mysterious unseen force pulling objects together, gravity, Einstein told the world, is a manifestation of the curvature of space-time caused by the presence of massive objects. But Einstein's theory wasn't born in a vacuum, not even the vacuum of space. Instead, the theory of general relativity relies upon complicated geometry; Einstein worked closely with mathematicians Marcel Grossmann, David Hilbert, Tullio Levi-Civita, and others as he pieced together his theory of gravity. In The Gravity of Math, the writer Steve Nadis and mathematician Shing-Tung Yau tell the story of how our view of the universe has been shaped and informed by mathematics, particularly when it comes to the enigmatic workings of gravity. Mathematicians have played a pivotal role in investigating relativity and gravity, gaining insights on phenomena like black holes, gravitational waves, and the Big Bang - in some cases uncovering key results decades, or even a century, before any experimental or observational data became available. An insightful and comprehensive study, The Gravity of Math explores how our understanding of math has defined our understanding of the universe. Gravity's reach is ostensibly boundless, and so is that of mathematics, which can carry us to the edge of infinity and back\"-- Provided by publisher.
Book
Transplanckian axions!?
A
bstract
We discuss quantum gravitational effects in Einstein theory coupled to periodic axion scalars to analyze the viability of several proposals to achieve superplanckian axion periods (aka decay constants) and their possible application to large field inflation models. The effects we study correspond to the nucleation of euclidean gravitational instantons charged under the axion, and our results are essentially compatible with (but independent of) the Weak Gravity Conjecture, as follows: single axion theories with superplanckian periods contain gravitational instantons inducing sizable higher harmonics in the axion potential, which spoil superplanckian inflaton field range. A similar result holds for multi-axion models with lattice alignment (like the Kim-Nilles-Peloso model). Finally, theories with
N
axions can still achieve a moderately superplanckian periodicity (by a
N
factor) with no higher harmonics in the axion potential. The Weak Gravity Conjecture fails to hold in this case due to the absence of some instantons, which are forbidden by a discrete
Z
N
gauge symmetry. Finally we discuss the realization of these instantons as euclidean D-branes in string compactifications.
Journal Article
Gravity : investigating the force, mass, and attraction of physical bodies
A look at various theories throughout history about gravity.
Book
Theory-agnostic searches of non-gravitational modes in the ringdown
We present a theory-agnostic framework to search for extra-fundamental modes in the ringdown phase of black hole mergers. These modes, distinct from standard General Relativity (GR) deviations, originate from modifications of the theory of gravity. Applying our method to the events GW150914, GW190521, and GW200129, we find no significant evidence for extra modes beyond those expected in GR.
Journal Article