Dynamical Four-Form Fields
We present an example of a gauge-invariant Lagrangian that contains four derivatives and describes one massive, non-ghostlike, degree of freedom.
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arXiv subjects
Luca Grisa
Publications and source records attributed to Luca Grisa.
Tachyonic Quintessence and a Preferred Direction in the Sky
We show that quintessence, when it is described by a tachyonic field, can amplify a tiny primordial gradient generating a preferred direction in the sky. In its simplest realization, this mechanism only affects the Cosmic Microwave Background fluctuations at the quadrupole level. We briefly discuss how higher multipoles can also be affected, once the full structure of the quintessence potential is taken into account.
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Pauli-Fierz Gravitons on Friedmann-Robertson-Walker Background
We derive the Hamiltonian describing Pauli-Fierz massive gravitons on a flat Friedmann-Robertson-Walker (FRW) cosmology in a particular, non-generic effective field theory. The cosmological evolution is driven by a scalar field Phi with an arbitrary potential V(Phi). The model contains two coupled scalar modes, corresponding to the fluctuations of Phi and to the propagating scalar component of the Pauli-Fierz graviton. In order to preserve the full gauge invariance of the massless version of the theory, both modes have to be taken into account. We canonically normalize the Hamiltonian and generalize the Higuchi bound to FRW backgrounds. We discuss how this bound can set limits on the value of the Pauli-Fierz mass parameter. We also observe that on a generic FRW background the speed of propagation of the scalar mode of the graviton is always smaller than the speed of light.
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Lorentz-Violating Massive Gravity in Curved Space
In models of modified gravity, extra degrees of freedom usually appear. They must be removed from the spectrum because they may indicate the presence of instabilities and because otherwise the model might not agree with observation. In the present letter, we will discuss a model that modifies General Relativity through the addition of a Lorentz-violating potential-like term for the metric. No additional propagating modes and no classical instabilities are present. The model departs from GR only in the extreme infrared region, and the cosmological evolution contains a bounce when the size of the Universe is of the same order of the added deformation.
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Dressed Domain Walls and Holography
The cutoff version of the AdS/CFT correspondence states that the Randall Sundrum scenario is dual to a Conformal Field Theory (CFT) coupled to gravity in four dimensions. The gravitational field produced by relativistic domain walls can be exactly solved in both sides of the correspondence, and thus provides one further check of it. We show in the two sides that for the most symmetric case, the wall motion does not lead to particle production of the CFT fields. Still, there are nontrivial effects. Due to the trace anomaly, the CFT effectively renormalizes the domain wall tension. On the five dimensional side, the wall is a codimension 2 brane localized on the Randall-Sundrum brane, which pulls the wall in a uniform acceleration. This is perceived from the brane as a domain wall with a tension slightly larger than its bare value. In both cases, the deviation from General Relativity appears at nonlinear level in the source, and the leading corrections match to the numerical factors.
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Delocalization from Anomaly Inflow and Intersecting Brane Dynamics
We study intersecting D-brane models, that describe at low energies a two dimensional chiral fermion theory localized at the intersection. The fermions are coupled to gauge fields in the bulk. The resulting low energy theory is equivalent to the Gross-Neveu model with dynamical chiral symmetry breaking. No Nambu-Goldstone boson associated with spontaneously broken symmetries appears in two dimensional field theories. In the present work we discuss solvable models with the same basic dynamics of the dual Gross-Neveu model. The disappearance of the Nambu-Goldstone boson is obtained from D-brane dynamics. The mechanism relies on the non-trivial dynamics of a gauge field due to anomaly inflow.
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Resonance in Asymmetric Warped Geometry
We study the spectrum of an asymmetric warped braneworld model with different AdS curvatures on either side of the brane. In addition to the RS-like modes we find a resonance state. Its mass is proportional to the geometric mean of the two AdS curvature scales, while the difference between them determines the strength of the resonance peak. There is a complementarity between the RS zero-mode and the resonance: making the asymmetry stronger weakens the zero-mode but strengthens the resonance, and vice versa. We calculate numerically the braneworld gravitational potential and discuss the holographic correspondence for the asymmetric model.
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Lorentz-violating massive gauge and gravitational fields
We study nonlinear dynamics in models of Lorentz-violating massive gravity. The Boulware-Deser instability restricts severely the class of acceptable theories. We identify a model that is stable. It exhibits the following bizarre but interesting property: there are only two massive propagating degrees of freedom in the spectrum, and yet long-range instantaneous interactions are present in the theory. We discuss this property on a simpler example of a photon with a Lorentz-violating mass term where the issues of (a)causality are easier to understand. Depending on the values of the mass parameter these models can either be excluded, or become phenomenologically interesting. We discuss a similar example with more degrees of freedom, as well as a model without the long-range instantaneous interactions.
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