1,720,998 research outputs found
External Stability for Spherically Symmetric Solutions in Lorentz Breaking Massive Gravity
No full textWe discuss spherically symmetric solutions for point-like sources in Lorentz-breaking massive gravity theories. This analysis is valid for Stückelberg’s effective field theory formulation, for Lorentz Breaking Massive Bigravity and general extensions of gravity leading to an extra term −Srγ added to the Newtonian potential. The approach consists in analyzing the stability of the geodesic equations, at the first order (deviation equation). The main result is a strong constrain in the space of parameters of the theories. This motivates higher order analysis of geodesic perturbations in order to understand if a class of spherically symmetric Lorentz-breaking massive gravity solutions, for self-gravitating systems, exists. Stable and phenomenologically acceptable solutions are discussed in the no-trivial case S ≠ 0
Nonlocal quantum field theory without acausality and nonunitarity at quantum level: is SUSY the key?
No full textThe realization of a nonlocal quantum field theory without losing unitarity, gauge invariance
and causality is investigated. It is commonly retained that such a formulation is
possible at tree level, but at quantum level acausality is expected to reappear at one loop.
We suggest that the problem of acausality is, in a broad sense, similar to the one about
anomalies in quantum field theory. By virtue of this analogy, we suggest that acausal
diagrams resulting from the fermionic sector and the bosonic one might cancel each
other, with a suitable content of fields and suitable symmetries. As a simple example,
we show how supersymmetry can alleviate this problem in a simple and elegant way,
i.e. by leading to exact cancellations of harmful diagrams, to all orders of perturbation
theory. An infinite number of divergent diagrams cancel each other by virtue of the
nonrenormalization theorem of supersymmetry. However, supersymmetry is not enough
to protect a theory from all acausal divergences. For instance, acausal contributions to
supersymmetric corrections to D-terms are not protected by supersymmetry. On the
other hand, we show in detail how supersymmetry also helps in dealing with D-terms:
divergences are not canceled but they become softer than in the nonsupersymmetric case.
The supergraphs’ formalism turns out to be a powerful tool to reduce the complexity of
perturbative calculations
Non-commutative quantum gravity phenomenology in underground experiments
No full textWe show how non-commutative spacetime models can induce Pauli Exclusion Principle (PEP) forbidden nuclear and atomic transitions. We focalize our analysis on one of the most popular instantiations of non-commutativeness: -Poincaré model, based on the Groenewold–Moyal plane algebra. We show that PEP violating transitions induced by -Poincaré have an energy scale and angular emission dependence. PEP violating transitions in nuclear and atomic systems can be tested with very high accuracy in underground laboratory experiments such as DAMA/LIBRA and VIP(2). We derive that the Equivalence Principle assumed -Poincaré model can be already ruled-out until the Planck scale, from nuclear transitions tests by DAMA/LIBRA experiment
Neutron Majorana mass from Exotic Instantons in a Pati-Salam model
Full text linkWe show how a Majorana mass for the neutron could result from nonperturbative quantum gravity effects peculiar to string theory. In particular, "exotic instantons" in un-oriented string compactifications with D-branes extending the (supersymmetric) standard model could indirectly produce an effective operator delta m n(t)n + h.c.. In a specific model with an extra vector-like pair of 'quarks', acquiring a large mass proportional to the string mass scale (exponentially suppressed by a function of the string moduli fields), delta m can turn out to be as low as 10(-24)-10(-25) eV.The induced neutron-antineutron oscillations could take place with a time scale tau(n (n) over tilde) > 10(8)s that could be tested by the next generation of experiments. On the other hand, proton decay and FCNC's are automatically strongly suppressed and are compatible with the current experimental limits.Depending on the number of brane intersections, the model may also lead to the generation of Majorana masses for R-handed neutrini. Our proposal could also suggest neutron-neutralino or neutron-axino oscillations, with implications in UCN, Dark Matter Direct Detection, UHECR and Neutron-Antineutron oscillations.This suggests to improve the limits on neutron-antineutron oscillations, as a possible test of string theory and quantum gravity
Testing Noncommutative Spacetimes and Violations of the Pauli Exclusion Principle with underground experiments
Full text linkWe propose to deploy limits that arise from different tests of the Pauli Exclusion Principle: i) to provide
theories of quantum gravity with experimental guidance; ii) to distinguish, among the plethora of possible models, the ones that are already ruled out by current data; iii) to direct future attempts to be in accordance with experimental constraints. We first review experimental bounds on nuclear processes forbidden by the Pauli Exclusion Principle, which have been derived by several experimental collaborations making use of various detector materials. Distinct features of the experimental devices entail sensitivities on the constraints hitherto achieved that may differ from one another by several orders of magnitude. We show that with choices of these limits, well-known examples of flat noncommutative space-time instantiations of quantum gravity can be heavily constrained, and eventually ruled out. We devote particular attention to the analysis of the k-Minkowski and theta-Minkowski noncommutative spacetimes.
These are deeply connected to some scenarios in string theory, loop quantum gravity, and noncommutative geometry.
We emphasize that the severe constraints on these quantum spacetimes, although they cannot rule out theories of
top-down quantum gravity to which they are connected in various ways, provide a powerful limitation for those
models. Focus on this will be necessary in the future
String memories...lost and regained
No full textWe discuss stringy alpha' corrections to the gravitational wave signal generated in the merging of two black holes. We model the merging with two BPS compact massive objects in the heterotic string, described by standard vertex operators or coherent states. Despite the expected cubic suppression in alpha' w.r.t. the General Relativity result in the low-energy expansion, at tree level the infinite tower of string resonances leaves a clear footprint on the gravitational wave signals within the sensitivity region of aLIGO/VIRGO and future interferometers. Including loop effects that broaden and destabilise the string resonances suggests a sort of lost stringy memory effect that can be regained through the analysis of the quasi normal modes in the ring-down phase
Constraining mirror dark matter inside neutron stars
Full text linkWe inspect the possibility that neutron star interiors are a mixture of ordinary matter and mirror dark matter. This is a scenario that can be naturally envisaged according to well studied accretion mechanisms, including the Bondi–Hoyle one. We show that the inclusion of mirror dark matter in neutron star models lowers the maximum neutron star mass for a given equation of state, and that it decreases the tidal deformability of a given neutron star. These general features imply that, given an equation of state, one can constrain the maximum viable amount of mirror dark matter in neutron stars in order to consistently fulfil existing maximum mass and tidal deformability constraints. Conversely, using tidal deformability measurements to rule out equations of state requires making assumptions on the amount of mirror dark matter contained in neutron stars. Finally, the presence of mirror dark matter also modifies the universal relation that links the tidal deformability of a neutron star to its compactness. Therefore, caution is mandatory when considering exotic models, such as the ones discussed in this paper
Phenomenology of the Pauli exclusion principle violations due to the non-perturbative generalized uncertainty principle
No full textNew phenomenological implications of the Generalized Uncertainty Principle (GUP), a modification of the Heisenberg Uncertainty Principle (HUP) are explored in light of constraints arising from underground experiments. An intimate link intertwines the symplectic structure of a theory, which is at the very base of the formulation of the HUP and thus a pillar of quantum mechanics, with the symmetries of space-time and the spin-statistics. Within this wide framework, a large class of non-perturbative GUPs inevitably lead to energy-dependent violations of the total angular momentum conservation rules, and imply hence tiny Pauli Exclusion Principle (PEP) violating transitions. Exotic PEP violating nuclear transitions can be tested, for example, through extremely high precision data provided by the DAMA/LIBRA experiment. We show that several GUP violations are already ruled out up to the quantum gravity Planck scale
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