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Xavier Calmet

Publications and source records attributed to Xavier Calmet.

At least 127 records · Page 7Linked to original sources
arXiv2005

Minimum Length from First Principles

We show that no device or gedanken experiment is capable of measuring a distance less than the Planck length. By "measuring a distance less than the Planck length" we mean, technically, resolve the eigenvalues of the position operator to within that accuracy. The only assumptions in our argument are causality, the uncertainty principle from quantum mechanics and a dynamical criteria for gravitational collapse from classical general relativity called the hoop conjecture. The inability of any gedanken experiment to measure a sub-Planckian distance suggests the existence of a minimal length.

hep-th↗
arXiv2005

Space-Time Symmetries of Noncommutative Spaces

We define a noncommutative Lorentz symmetry for canonical noncommutative spaces. The noncommutative vector fields and the derivatives transform under a deformed Lorentz transformation. We show that the star product is invariant under noncommutative Lorentz transformations. We then apply our idea to the case of actions obtained by expanding the star product and the fields taken in the enveloping algebra via the Seiberg-Witten maps and verify that these actions are invariant under these new noncommutative Lorentz transformations. We finally consider general coordinate transformations and show that the metric is undeformed.

hep-th↗
arXiv2004

Chiral Fermions and Quadratic Divergences

In an approach towards naturalness without supersymmetry, renormalization properties of nonsupersymmetric abelian quiver gauge theories are studied. In the construction based on cyclic groups Z_p the gauge group is U(N)^p, the fermions are all in bifundamentals and the construction allows scalars in adjoints and bifundamentals. Only models without adjoint scalars, however, exhibit both chiral fermions and the absence of one-loop quadratic divergences in the scalar propagator.

hep-th↗
arXiv2004

Minimum Length from Quantum Mechanics and Classical General Relativity

We derive fundamental limits on measurements of position, arising from quantum mechanics and classical general relativity. First, we show that any primitive probe or target used in an experiment must be larger than the Planck length, $l_P$. This suggests a Planck-size {\it minimum ball} of uncertainty in any measurement. Next, we study interferometers (such as LIGO) whose precision is much finer than the size of any individual components and hence are not obviously limited by the minimum ball. Nevertheless, we deduce a fundamental limit on their accuracy of order $l_P$. Our results imply a {\it device independent} limit on possible position measurements.

hep-th↗
arXiv2004

Dynamics of the Fisher Information Metric

We present a method to generate probability distributions that correspond to metrics obeying partial differential equations generated by extremizing a functional $J[g^{μν}(θ^i)]$, where $g^{μν}(θ^i)$ is the Fisher metric. We postulate that this functional of the dynamical variable $g^{μν}(θ^i)$ is stationary with respect to small variations of these variables. Our approach enables a dynamical approach to Fisher information metric. It allows to impose symmetries on a statistical system in a systematic way. This work is mainly motivated by the entropy approach to nonmonotonic reasoning.

cond-mat.stat-mech↗
arXiv2004

Minimal Grand Unification Model in an Anthropic Landscape

It has been recently pointed out by Arkani-Hamed and Dimopoulos that if the universe is a landscape of vacua, and if therefore fine-tuning is not a valid guidance principle for searching for physics beyond the standard model, supersymmetric unification only requires the fermionic superpartners. We argue that in that landscape scenario, the fermionic superpartners are not needed for unification, which can be achieved in SO(10) either via a direct breaking to the standard model at the grand unification scale or through an intermediate gauge symmetry. In most minimal SO(10) models, the proton lifetime is long enough to avoid the experimental bounds. These models are the truly minimal fine-tuned extensions of the standard model in the sense proposed by Davoudiasl et al..

hep-ph↗
arXiv2004

Metric on a Statistical Space-Time

We introduce a concept of distance for a space-time where the notion of point is replaced by the notion of physical states e.g. probability distributions. We apply ideas of information theory and compute the Fisher information matrix on such a space-time. This matrix is the metric on that manifold. We apply these ideas to a simple model and show that the Lorentzian metric can be obtained if we assumed that the probability distributions describing space-time fluctuations have complex values. Such complex probability distributions appear in non-Hermitian quantum mechanics.

math-ph↗
arXiv2004

What are the Bounds on Space-Time Noncommutativity?

In this article we consider the bounds on the noncommutative nature of space-time. We argue that these bounds are extremely model dependent. In the only phenomenologically viable framework, i.e. when the fields are taken to be in the enveloping of the Lie algebra, the constraints are fairly loose and only of the order of a few TeV.

hep-ph↗
arXiv2003

Effective Field Theories on Non-Commutative Space-Time

We consider Yang-Mills theories formulated on a non-commutative space-time described by a space-time dependent anti-symmetric field $θ^{μν}(x)$. Using Seiberg-Witten map techniques we derive the leading order operators for the effective field theories that take into account the effects of such a background field. These effective theories are valid for a weakly non-commutative space-time. It is remarkable to note that already simple models for $θ^{μν}(x)$ can help to loosen the bounds on space-time non-commutativity coming from low energy physics. Non-commutative geometry formulated in our framework is a potential candidate for new physics beyond the standard model.

hep-ph↗
arXiv2003

Softening the Naturalness Problem

It was observed by Veltman a long time ago that a special value for the Higgs boson mass could lead to a cancellation of the quadratically divergent corrections to the Higgs boson's squared mass which appear at one loop. We present a class of low energy models that allow to soften the naturalness problem in the sense that there can be a cancellation of radiative corrections appearing at one loop. The naturalness problem is shifted from the one TeV region to the 10 TeV region. Depending on the specific model under consideration, this scale can even be shifted to a higher energy scale. Signatures of these models are discussed.

hep-ph↗
arXiv2002

Symmetry Breaking and Time Variation of Gauge Couplings

Astrophysical indications that the fine structure constant has undergone a small time variation during the cosmological evolution are discussed within the framework of the standard model of the electroweak and strong interactions and of grand unification. A variation of the electromagnetic coupling constant could either be generated by a corresponding time variation of the unified coupling constant or by a time variation of the unification scale, of by both. The various possibilities, differing substantially in their implications for the variation of low energy physics parameters like the nuclear mass scale, are discussed. The case in which the variation is caused by a time variation of the unification scale is of special interest. It is supported in addition by recent hints towards a time change of the proton-electron mass ratio. Implications for the analysis of the Oklo remains and for quantum optics tests are discussed.

hep-ph↗
arXiv2002

The Cosmological Evolution of the Nucleon Mass and the Electroweak Coupling Constants

Starting from astrophysical indications that the fine structure constant might undergo a small cosmological time shift, we discuss the implications of such an effect from the point of view of particle physics. Grand unification implies small time shifts for the nucleon mass, the magnetic moment of the nucleon and the weak coupling constant as well. The relative change of the nucleon mass is about 40 times larger than the relative change of alpha. Laboratory measurements using very advanced methods in quantum optics might soon reveal small time shifts of the nucleon mass, the magnetic moment of the nucleon and the fine structure constant.

hep-ph↗
arXiv2001

Radiative Lepton Decays and the Substructure of Leptons

The leptons are viewed as composite objects, exhibiting anomalous magnetic moments and anomalous flavor-changing transition moments. The decay μ\to e γis expected to occur with a branching ratio of the same order as the present experimental limit. The first order QED radiative correction is considered.

hep-ph↗
arXiv2001

Calculation of the Higgs Boson Mass Using the Complementarity Principle

We compute the Higgs mass in a model for the electroweak interactions based on a confining theory. This model is related to the standard model by the complementarity principle. A dynamical effect due to the large typical scale of the Higgs boson shifts its mass above that of the W-bosons. We obtain m_H=129.6 GeV.

hep-ph↗
arXiv2001

Kaluza-Klein Theories and the Anomalous Magnetic Moment of the Muon

We discuss nonminimal couplings of fermions to the electromagnetic field, which generically appear in models with extra dimensions. We consider models where the electromagnetic field is generated by the Kaluza-Klein mechanism. The nonminimal couplings contribute at tree-level to anomalous magnetic and electric dipole moments of fermions. We use recent measurements of these quantities to put limits on the parameters of models with extra dimensions.

hep-ph↗
arXiv2001

Electroweak D-Waves

We consider phenomenological implications of a model recently proposed for the electroweak interactions based on a SU(2)_L confining theory. We concentrate on the production of excited states of the electroweak bosons at future colliders and we consider their contribution to the reaction W^+ + W^- \to W^+ + W^-. We expect large deviations from the standard model in the TeV region.

hep-ph↗