arXiv subjects

Luis Gonzalez-Mestres

Publications and source records attributed to Luis Gonzalez-Mestres.

At least 19 recordsLinked to original sources

arXiv2014

CMB B-modes, spinorial space-time and Pre-Big Bang (II)

The BICEP2 collaboration reported recently a B-mode polarization of the cosmic microwave background (CMB) radiation inconsistent with the null hypothesis at a significance of > 5 σ. This result has been often interpreted as a signature of primordial gravitational waves from cosmic inflation, even if actually polarized dust emission may be at the origin of such a signal. Even assuming that part of this CMB B-mode polarization really corresponds to the early Universe dynamics, its interpretation in terms of inflation and primordial gravitational waves is not the only possible one. Alternative cosmologies such as pre-Big Bang patterns and the spinorial space-time (SST) we introduced in 1996-97 can naturally account for such CMB B-modes. In particular, the SST automatically generates a privileged space direction (PSD) whose existence may have been confirmed by Planck data. If such a PSD exists, it seems normal to infer that vector perturbations have been present in the early Universe leading to CMB B-modes in suitable cosmological patterns. Inflation would not be required to explain the BICEP2 result assuming it really contains a primordial signal. More generally, pre-Big Bang cosmologies can also generate gravitational waves in the early Universe without any need for cosmic inflation. We further discuss here possible alternatives to the inflationary interpretation of a primordial B-mode polarization of cosmic microwave background radiation.

physics.gen-ph↗

arXiv2012

Pre-Big Bang, vacuum and noncyclic cosmologies

WMAP and Planck open the way to unprecedented Big Bang phenomenology, potentially allowing to test the standard Big Bang model as well as less conventional approaches including noncyclic pre-Big Bang cosmologies that would incorporate a new fundamental scale beyond the Planck scale and, possibly, new ultimate constituents of matter. Alternatives to standard physics can be considered from a cosmological point of view concerning vacuum structure, the nature of space-time, the origin and evolution of our Universe, the validity of quantum field theory and conventional symmetries, solutions to the cosmological constant problem, inflationary scenarios, dark matter and dark energy, the interpretation of string-like theories... Lorentz-like symmetries for the properties of matter (standard or superbradyonic) can then be naturally stable space-time configurations resulting from general cosmological scenarios that incorporate physics beyond the Planck scale and describe the formation and evolution of the present vacuum. But an even more primordial question seems to be that of the origin of half-integer spins, that cannot be generated through orbital angular momentum in the usual real space-time. It turns out that the use of a spinorial space-time with two complex coordinates instead of the conventional four real ones presents several attractive features. Taking the cosmic time to be the modulus of a SU(2) spinor leads by purely geometric means to a naturally expanding universe, with a ratio between cosmic relative velocities and distances equal to the inverse of the age of the Universe. No reference to standard matter, hidden fields, gravitation or relativity is required to get such a result that looks quite reasonable from an observational point of view. We discuss basic ideas and phenomenological issues for noncyclic pre-Big Bang cosmologies in the present context.

physics.gen-ph↗

arXiv2012

Testing fundamental principles with high-energy cosmic rays

It is not yet clear whether the observed flux suppression for ultra-high energy cosmic rays (UHECR) at energies above \simeq 4.10E19 eV is a signature of the Greisen-Zatsepin-Kuzmin (GZK) cutoff or corresponds, for instance, to the maximum energies available at the relevant sources. Both phenomena can be sensitive to violations of standard special relativity modifying cosmic-ray propagation or acceleration at very high energy, and would in principle allow to set bounds on Lorentz symmetry violation (LSV) parameters. But the precise phenomenological analysis of the experimental data is far from trivial, and other effects can be present. The effective parameters can be directly linked to Planck-scale physics or to physics beyond Planck scale. If a vacuum rest frame (VRF) exists, LSV can modify the internal structure of particles at very high energy. Conventional symmetries may also cease to be valid at energies close to the Planck scale. Other possible violations of fundamental principles and conventional basic hypotheses (quantum mechanics, quark confinement, energy and momentum conservation, vacuum homogeneity and "static" properties, effective space dimensions...) can also be considered and possibly tested in high-energy cosmic-ray experiments. Even below UHE (ultra-high energy), exotic signatures cannot be excluded. We present an updated discussion of the theoretical and phenomenological situation, including prospects for earth-based and space experiments and a simple potential interpretation of the observed UHECR composition in terms of LSV where the GZK cutoff would be replaced by spontaneous emission of photons or e+ e- pairs. As the OPERA result on a possible superluminal propagation of the muon neutrino was announced after the conference, we briefly comment on the consistency problems that a \simeq 2.5 x 10E-5 critical speed anomaly for the muon neutrino can raise.

hep-ph↗

arXiv2011

WMAP, Planck, cosmic rays and unconventional cosmologies

The claim by Gurzadyan et al. that the cosmological sky is a weakly random one where "the random perturbation is a minor component of mostly regular signal" has given rise to a series of useful exchanges. The possibility that the Cosmic Microwave Background radiation (CMB) data present trends in this direction would have strong implications for unconventional cosmologies. Similarly, data on ultra-high energy cosmic rays may contain signatures from new Physics generated beyond the Planck scale. It therefore seems legitimate, from a phenomenological point of view, to consider pre-Big Bang cosmologies as well as patterns where standard particles would not be the ultimate constituents of matter and the presently admitted principles of Physics would not necessarily be the fundamental ones. We discuss here prospects for some noncyclic, nonstandard cosmologies.

physics.gen-ph↗

arXiv2011

Astrophysical consequences of the OPERA superluminal neutrino

A simple discussion of the recent OPERA result on the apparent critical speed of the muon neutrino is presented. We point out in particular some of the possible consistency problems of such an interpretation of the OPERA data with respect to well-established astrophysical observations.

physics.gen-ph↗

arXiv2011

Comments on the recent result of the "Measurement of the neutrino velocity with the OPERA detector in the CNGS beam"

The recent result by the OPERA experiment, confirming a trend already present in a previous result by MINOS, raises the question of a possible strong violation of standard relativity. In particular, the particles of the standard model would have different critical speeds in vacuum, and such differences would be measurable with nowadays facilities. Although several experimental and phenomenological issues remain open, the situation deserves been studied closely from a theoretical point of view. The data cannot be explained by conventional extrapolations of Planck-scale Lorentz symmetry violation (LSV) patterns. But, as already stressed in our previous papers since 1995, a weak mixing of standard particles with superbradyons (particles with positive mass and energy, and a critical speed in vacuum much larger than the speed of light) can explain such an effect. Superbradyons can be the ultimate constituents of matter (superluminal preons), but they may simultaneously exist in our Universe as free particles just as light can cross a transparent material medium. In this case, a direct mixing between superbradyons and the particles of the standard model would be unavoidable. After briefly examining the experimental situation and the problems it may raise, we comment on the possibility of a superbradyonic mixing, as well as on the implications of a spinorial description of space-time where space translations would form a SU(2) compact group.

physics.gen-ph↗

arXiv2011

Cosmic rays and tests of fundamental principles

It is now widely acknowledged that cosmic rays experiments can test possible new physics directly generated at the Planck scale or at some other fundamental scale. By studying particle properties at energies far beyond the reach of any man-made accelerator, they can yield unique checks of basic principles. A well-known example is provided by possible tests of special relativity at the highest cosmic-ray energies. But other essential ingredients of standard theories can in principle be tested: quantum mechanics, uncertainty principle, energy and momentum conservation, effective space-time dimensions, hamiltonian and lagrangian formalisms, postulates of cosmology, vacuum dynamics and particle propagation, quark and gluon confinement, elementariness of particles... Standard particle physics or string-like patterns may have a composite origin able to manifest itself through specific cosmic-ray signatures. Ultra-high energy cosmic rays, but also cosmic rays at lower energies, are probes of both "conventional" and new Physics. Status, prospects, new ideas, and open questions in the field are discussed. The Post Scriptum shows that several basic features of modern cosmology naturally appear in a SU(2) spinorial description of space-time without any need for matter, relativity or standard gravitation. New possible effects related to the spinorial space-time structure can also be foreseen. Similarly, the existence of spin-1/2 particles can be naturally related to physics beyond Planck scale and to a possible pre-Big Bang era.

astro-ph.HE↗

arXiv2011

Lorentz symmetry violation, dark matter and dark energy

Taking into account the experimental results of the HiRes and AUGER collaborations, the present status of bounds on Lorentz symmetry violation (LSV) patterns is discussed. Although significant constraints will emerge, a wide range of models and values of parameters will still be left open. Cosmological implications of allowed LSV patterns are discussed focusing on the origin of our Universe, the cosmological constant, dark matter and dark energy. Superbradyons (superluminal preons) may be the actual constituents of vacuum and of standard particles, and form equally a cosmological sea leading to new forms of dark matter and dark energy.

astro-ph.CO↗

arXiv2010

Superbradyons and some possible dark matter signatures

Superluminal preons (superbradyons) with a critical speed in vacuum much larger than the speed of light would, if they exist, play a fundamental role as constituents of the physical vacuum and of the conventional particles considered in standard theories. Then, standard Lorentz symmetry and quantum mechanics would not be ultimate fundamental properties of space-time and matter. If superbradyons are present as free particles in our Universe, they are expected to couple very weakly to "ordinary" matter, but they can spontaneously decay by emitting standard particles until they reach a speed equal or close to that of light. They would then form a cosmological sea where the relation between inertial and gravitational masses would differ from conventional Physics. Superbradyons may be at the origin of cosmological and astrophysical phenomena usually associated to dark matter, dark energy and inflation. They can also be a source of conventional cosmic rays of all energies. In such a scenario, superbradyon spontaneous decays and similar interactions would be candidates to explain data on electron and positron abundances (PAMELA, ATIC, Fermi LAT, HESS, PPB-BETS) considered as possible dark matter signatures. Superbradyons emitting this radiation may even have comparatively small inertial masses, and kinetic energies not far away from those of the decay events. But in most cases, such "light" superbradyons could not be found at accelerator experiments. We comment on several basic physics and phenomenological issues in connection with the superbradyon hypothesis.

astro-ph.CO↗

arXiv2010

Lorentz violation, vacuum, cosmic rays, superbradyons and Pamir data

The possibility that Pamir data at very high energy cannot be fully explained by standard physics has recently led to the suggestion that the peculiar jet structure observed above ~ 10E16 eV could be due to a suppression of effective space transverse dimensions. The new pattern considered violates Lorentz symmetry. We point out that, in models with Lorentz symmetry violation, a suppression of available transverse energy for jets while conserving longitudinal momentum can be generated by new forms of energy losses at very high energy without altering space-time structure. An illustrative example can be superbradyon emission, where in all cases the superbradyon energy would be much larger than its momentum times c (speed of light). More generally, such phenomena could be due to the interaction of the high-energy cosmic ray with new vacuum and/or particle structure below the 10E-20 cm scale. Scenarios involving Lorentz symmetry violation but not superbradyons are also briefly considered.

astro-ph.HE↗

arXiv2009

Preon models, relativity, quantum mechanics and cosmology (I)

Preons are hypothetic constituents of the standard particles. They were initially assumed to have basically similar properties to those of conventional matter. But this is not necessarily the case: the ultimate constituents of matter may feel a different space-time from that of special relativity and exhibit mechanical properties different from those predicted by standard quantum mechanics. They can also play an important cosmological role (inflation, dark matter, dark energy...). It is even not obvious that energy and momentum would have to be conserved in such a scenario. In this series of papers, we review the subject using the superbradyon model as an example, and suggest new ways to explore possible tests of the preon hypothesis.

physics.gen-ph↗

arXiv2009

AUGER-HiRes results and models of Lorentz symmetry violation

The implications of AUGER and HiRes results for patterns of Lorentz symmetry violation (LSV) are examined, focusing on weak doubly special relativity (WDSR). If the Greisen-Zatsepin-Kuzmin (GZK) cutoff is definitely confirmed, the mass composition of the highest-energy cosmic-ray spectrum will be a crucial issue to draw precise theoretical consequences from the experimental results. Assuming that the observed flux suppression is due to the GZK mechanism, data will allow in principle to exclude a significant range of LSV models and parameters, but other important possibilities are expected to remain open : Lorentz breaking can be weaker or occur at a scale higher than the Planck scale, unconventional LSV effects can fake the GZK cutoff, threshold phenomena can delay its appearance... Space experiments appear to be needed to further test special relativity. We also examine the consequences of AUGER and HiRes data for superbradyons. If such superluminal ultimate constituents of matter exist in our Universe, they may provide new forms of dark matter and dark energy.

astro-ph.HE↗

arXiv2008

Lorentz symmetry violation and the results of the AUGER experiment

We briefly discuss the implications of recent AUGER results for patterns of Lorentz symmetry violation (LSV), assuming that the existence of the Greisen-Zatsepin-Kuzmin cutoff is definitely confirmed. The mass composition of the highest-energy cosmic-ray spectrum is a crucial issue. In any case, the new data allow in principle to exclude a significant range of LSV models but leave open several important possibilities : a weaker Lorentz breaking, a fundamental scale beyond the Planck scale, scenarios with threshold effects... It may even happen that spontaneous decays due to LSV fake the GZK cutoff. Space experiments appear to be needed to further test special relativity. We also comment on the consequences of AUGER data for superbradyons. If such particles are present in the Universe, they may provide new forms of dark matter and dark energy.

hep-ph↗

arXiv2006

Weak doubly special relativity and ultra-high energy cosmic ray experiments

Should projects of space experiments on ultra-high energy cosmic rays be supported, whatever AUGER results will turn out to be? We claim that this is indeed the case. It is now widely admitted that models of Lorentz symmetry violation (LSV) at the Planck scale based on power-like extrapolations down to cosmic-ray scales and able to account for a possible absence of the Greisen-Zatsepin-Kuzmin cutoff exist and require the existence of a privileged inertial rest frame, as we proposed in 1997 (paper physics/9704017 and subsequent work). The favoured energy dependence of the LSV parameter will then be quadratic rather than linear. This approach (weak doubly special relativity, WDSR) is different from the version of doubly special relativity defended by several authors, where the laws of Physics are required to be exactly identical in all inertial reference frames (strong doubly special relativity, SDSR). To date, WDSR patterns based on a deformation of special relativity with a privileged (vacuum) rest frame are the only clear and consistent candidate to explain a possible absence of the GZK cutoff invoking deviations from standard relativity. It is also to be emphasized, as in hep-ph/0510361, that the usual hypothesis of a power-like dependence of the LSV effective parameters not being altered by any intermediate energy scale is not the only possible one. Therefore, experiments sensitive to UHCR energies as high as possible become necessary irrespective of AUGER results.

hep-ph↗

arXiv2005

On extrapolations below the Planck scale in models with Lorentz symmetry violation (I)

Most current models of Lorentz symmetry violation (LSV) at the Planck scale involve power-like extrapolations of the Lorentz-beaking term down to accelerator and even much lower energies. It is therefore assumed that no intermediate energy scale alters this behaviour. But this is not the only possible scenario: a more sophisticate energy-dependence is possible, and would even be natural, involving significant effective thresholds at intermediate energies. Such thresholds may exist between the Planck scale and the highest cosmic-ray energies, or between ultra-high cosmic-ray energies and the TeV scale, leading to interesting scenarios. In many cases, experimental predictions of LSV patterns can be dramatically modified and space experiments become necessary irrespective of AUGER results. By combining both kinds of experiments, future results of cosmic-ray observations will hopefully be able to test, for a large family of models involving various patterns of Planck-scale physics, the possible existence of an absolute local rest frame in the real world.

hep-ph↗

arXiv2004

Superluminal Particles, Cosmology and Cosmic-Ray Physics

Non-tachyonic superluminal sectors of matter (superbradyons), with critical speeds in vacuum much larger than the speed of light, can quite naturally exist and play an important role in both cosmic-ray physics (anomalous high-energy events) and cosmology (big-bang physics, alternatives to inflation, dark matter...). They can even be the real "elementary" particles. An updated discussion of the subject is presented, in relation with recent theoretical and experimental results. Prospects for future searches are also reexamined. Lorentz symmetry violation (LSV) models based on mixing with superbradyons are compared with LDRK (linearly deformed relativistic kinematics) and QDRK (quadratically deformed relativistic kinematics) such as defined in our previous paper physics/0003080 .

astro-ph↗

arXiv2004

Testing Scenarios of Lorentz Symmetry Violation Generated at the Planck Scale

Using new theoretical tools, which allow to better understand ultra-high energy (UHE) dynamics, several patterns of Lorentz symmetry violation (LSV) are studied and compared with experiment. It is claimed that quadratically deformed relativistic kinematics (QDRK), where the parameter driving LSV varies like the square of the energy scale, remains the best suited pattern to describe LSV generated at the Planck scale. Implications of existing data are discussed and prospects are presented having in mind next-generation experiments.

hep-ph↗

arXiv2004

Internal Structure of Ultra-High Energy Particles with Lorentz Symmetry Violation at the Planck Scale

Assuming the existence of a local vacuum rest frame (LVRF), and using suitable algebraic tranformations, the internal structure of ultra-high energy particles (UHEPs) is studied in the presence of Lorentz symmetry violation (LSV) at the Planck scale. Violations of the standard Lorentz contraction and time dilation formulae are made explicit. Dynamics in the rest frame of a UHEP is worked out and discussed. Phenomenological implications for ultra-high energy cosmic rays (UHECR), including possible violations of the Greisen-Zatsepin-Kuzmin GZK) cutoff, are studied for several LSV models.

hep-th↗