arXiv subjects

Pierre Fayet

Publications and source records attributed to Pierre Fayet.

At least 37 records · Page 2Linked to original sources

arXiv2016

The light U boson as the mediator of a new force, coupled to a combination of Q, B, L and dark matter

A new light gauge boson $U$ may have both vector and axial couplings. In a large class of theories however, the new $U(1)$ current $J^μ_F$ naturally combines with the weak neutral current $J^μ_{Z_{\rm sm}}$, both parity-violating, into a vectorial current $J^μ_U$, combination of the $B,\,L$ and electromagnetic currents with a possible dark matter current. $U^μ$ may be expressed equivalently as $\cosξ\,C^μ\! + \sin ξ\,Z^μ_{\rm \,sm}$ ("mixing with the $Z$") or $(1/\cosχ) \,\hat C^μ+\tanχ\,A^μ$ ("mixing with the photon"), with $\hat C$ coupled to $B,\,L$ and dark matter. The $U$ boson may be viewed as a generalized dark photon, coupled to SM particles through $Q_U=Q+λ_B B+λ_i L_i$, with strength $\,g"\cosξ\,\cos^2θ=e\tanχ$. "Kinetic mixing" terms, gauge invariant or not, simply correspond to a description in a non-orthogonal field basis (rather than to a new physical effect), with the dark photon in general also coupled to $B$ and $L$. In a grand-unified theory $\,Q_U^{\rm gut}=Q-2\,(B-L)\,$ at the GUT scale for SM particles, invariant under the $SU(4)$ electrostrong symmetry group, with a non-vanishing $ε= \tanχ$ already present at the GUT scale, leading to $Q_U\simeq \,Q-1.64\, (B-L)\,$ at low energy. This also applies, for a very light or massless $U$ boson, to a new long-range force, which could show up through apparent violations of the Equivalence Principle.

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arXiv2015

Scalar Bosons and Supersymmetry

The recent discovery of a spin-0 Brout-Englert-Higgs boson leads to further enquire about other fundamental scalars. Supersymmetric theories involve, in relation with the electroweak breaking, five such scalars at least, two charged and three neutral ones, usually denoted as H$^\pm$, H, h and A. They also introduce spin-0 squarks and sleptons as the superpartners of quarks and leptons. Supersymmetric extensions of the standard model lead to the possibility of gauge/BEH unification by providing spin-0 bosons as extra states for spin-1 gauge bosons within massive gauge multiplets. Depending on its properties the 125 GeV boson observed at CERN may then also be interpreted, up to a mixing angle induced by supersymmetry breaking, as the spin-0 partner of the Z under two supersymmetry transformations, i.e. as a Z that would be deprived of its spin.

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arXiv2015

The Supersymmetric Standard Model

The Standard Model may be included within a supersymmetric theory, postulating new sparticles that differ by half-a-unit of spin from their standard model partners, and by a new quantum number called R-parity. The lightest one, usually a neutralino, is expected to be stable and a possible candidate for dark matter. The electroweak breaking requires two doublets, leading to several charged and neutral Brout- Englert-Higgs bosons. This also leads to gauge/Higgs unification by providing extra spin-0 partners for the spin-1 W$^\pm$ and Z. It offers the possibility to view, up to a mixing angle, the new 125 GeV boson as the spin-0 partner of the Z under two supersymmetry transformations, i.e. as a Z that would be deprived of its spin. Supersymmetry then relates two existing particles of different spins, in spite of their different gauge symmetry properties, through supersymmetry transformations acting on physical fields in a non-polynomial way. We also discuss how the compactification of extra dimensions, relying on R-parity and other discrete symmetries, may determine both the supersymmetry-breaking and grand-unification scales

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arXiv2014

The BE-Higgs boson as spin-0 partner of the Z, in the Supersymmetric Standard Model

Supersymmetric extensions of the standard model lead to gauge/BE-Higgs unification by providing spin-0 bosons as extra states for spin-1 gauge bosons within massive gauge multiplets. They may be described by the spin-0 components of massive gauge superfields (instead of chiral superfields as usual). In particular, the 125 GeV boson observed at CERN, considered as a BEH boson associated with electroweak breaking and mass generation, may also be interpreted, up to a mixing angle induced by supersymmetry breaking, as the spin-0 partner of the Z under two supersymmetry transformations, i.e. as a Z that would be deprived of its spin.

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arXiv2010

Invisible Upsilon decays into Light Dark Matter

Invisible psi and Upsilon decays into light neutralinos, within the MSSM or N(n)MSSM, are smaller than for nu nubar production, even if light spin-0 particles are coupled to quarks and neutralinos. In a more general way, light dark matter particles are normally forbidden, unless they can annihilate sufficiently through a new interaction stronger than weak interactions (at lower energies), as induced by a light spin-1 U boson, or heavy-fermion exchanges in the case of scalar dark matter. We discuss the possible contributions of U-boson, heavy-fermion, or spin-0 exchanges to invisible psi and Upsilon decays. U-exchanges could lead, but not necessarily, to significant branching fractions for invisible decays into light dark matter. We show how one can get the correct relic density together with sufficiently small invisible branching fractions, and the resulting constraints on the U couplings to ordinary particles and dark matter, in particular |c_chi.f_bV| < 5 10^-3 from Upsilon decays, for 2 m_chi smaller than a few GeV. We also explain why there is no model-independent way to predict psi and Upsilon branching fractions into light dark matter, from dark matter annihilation cross sections at freeze-out time.

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arXiv2009

U(1)_A symmetry in two-doublet models, U bosons or light scalars, and psi and Upsilon decays

psi and Upsilon decays may be used to search for light neutral spin-1 or spin-0 bosons associated with a broken extra-U(1) symmetry, local or global, acting axially on quarks and leptons, as may be present in supersymmetric theories with a lambda H_1 H_2 S superpotential term. Recent data on Upsilon --> gamma + invisible neutral constrain an axial, pseudoscalar or scalar coupling to b to f_bA < 4 10^-7 m_U(MeV)/ sqrt B_inv, f_bP < 4 10^-3/ sqrt B_inv or f_bS < 6 10^-3/ sqrt B_inv, respectively. This also constrains, from universality properties, couplings to electrons to f_eA < 4 10^-7 m_U(MeV)/ sqrt B_inv, f_eP < 4 10^-7/ sqrt B_inv or f_eS < 6 10^-7/ sqrt B_inv. The pseudoscalar a (possibly traded for a light gauge boson, or scalar particle) should then be, for invisible decays of the new boson, for > 96 % singlet and < 4 % doublet, for tan beta > 1. Or, more generally, < 4 % /(tan^2 beta B_inv) doublet, which implies a very small rate for the corresponding psi decay, B (psi --> gamma + neutral) B_inv <~ 10^-6/ tan^4 beta. Similar results are obtained for new spin-1 or spin-0 neutral bosons decaying into mu+ mu-.

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arXiv2007

U-boson production in e+e- annihilations, psi and Upsilon decays, and Light Dark Matter

We recall how a new light gauge boson emerged in Supersymmetric extensions of the Standard Model with an extra singlet superfield, and how it could behave very much as a light pseudoscalar, with the corresponding symmetry broken at a scale higher than electroweak. Such a new gauge boson U, light and very weakly coupled, allows for Light Dark Matter particles, which could be at the origin of the 511 keV line from the galactic bulge. Could it be found directly in e+e- annihilations ? Not so easily, due to various constraints on its couplings, especially axial ones, leading to an axionlike behavior or extra parity-violation effects. Searches for the decay Upsilon -> gamma + invisible U may be used to constrain severely its axial coupling to the electron, f_eA = f_bA, to be less than about 10^-6 m_U(MeV). The vector coupling to the electron may in principle be larger. We find from g_mu-2, under reasonable assumptions, that this coupling can be at most as large as ~ 1.3 10^-3, for m_U < m_mu. Such a coupling of the order of 10^-3 could also be responsible for the somewhat large value of g_mu-2, compared to Standard Model expectations. The U couplings to electrons are otherwise likely to be smaller, e.g. \lsim 3 10^-6 m_U(MeV), if the couplings to neutrinos and electrons are similar. This restricts significantly the possibility of detecting a light U boson in e+e- -> gamma U. Despite that, U exchanges can provide annihilation cross sections of LDM particles of the appropriate size, even if this may require that light dark matter be relatively strongly self-interacting.

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arXiv2006

Constraints on Light Dark Matter and U bosons, from psi, Upsilon, K+, pi0, eta and eta' decays

Following searches for photinos and very light gravitinos in invisible decays of psi and Upsilon, we discuss new limits on Light Dark Matter and U bosons, from psi and Upsilon decays, as well as rare decays of K+ and invisible decays of pi0, eta and eta' ... . The new limits involving the vector couplings of the U to quarks turn out, not surprisingly, to be much less restrictive than existing ones on axial couplings, from an axionlike behavior of a light U boson, tested in psi --> gamma U, Upsilon --> gamma U and K+ --> pi+ U decays (or as compared to the limit from parity-violation in atomic physics, in the presence of an axial coupling to the electron). Altogether the hypothesis of light U bosons, and light dark matter particles, remains compatible with particle physics constraints, while allowing for the appropriate annihilation cross sections required, both at freeze-out (for the relic abundance) and nowadays (if e+ from LDM annihilations are at the origin of the 511 keV line from the galactic bulge).

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arXiv2006

U-boson detectability, and Light Dark Matter

The possible existence of a new gauge boson U, light and very weakly coupled, allows for Light Dark Matter particles, which could also be at the origin of the 511 keV line from the galactic bulge. Independently of dark matter, and taking into account possible Z-U mixing effects, we show that, even under favorable circumstances (no axial couplings leading to an axionlike behavior or extra parity-violation effects, very small coupling to neutrinos), and using reasonable assumptions (no cancellation effect in g(mu)-2, lepton universality), the U coupling to electrons can be at most as large as ~ 1.5 10^-3 (for m(U) < m(mu)), and is likely to be smaller (e.g. <~ 3 10^-6 m(U) (MeV), if the U couplings to neutrinos and electrons are similar). This restricts significantly the detectability of a light U in e+e- --> gamma U, in particular. U exchanges can still provide annihilation cross sections of LDM particles of the appropriate size, even if this may require that light dark matter be relatively strongly self-interacting.

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arXiv2006

Soft gamma-ray background and light Dark Matter annihilation

The bulk of the extragalactic background between 10 keV and 10 GeV is likely to be explained by the emission of Seyfert galaxies, type Ia supernovae, and blazars. However, as revealed by the INTEGRAL satellite, the bulge of our galaxy is an intense source of a 511 keV gamma-ray line, indicating the production of a large number of positrons that annihilate. The origin of the latter is debated, and they could be produced, in particular, by the (S- or P-wave) annihilation of light Dark Matter particles into e+e-. In any case, the cumulated effect of similar sources at all redshifts could lead to a new background of hard X-ray and soft gamma-ray photons. On the basis of the hierarchical model of galaxy formation, we compute analytically the SNIa contribution to the background, and add it to Seyfert and blazars emission models. We find that any extra contribution to this unresolved background at 511 keV should be lower than about 4 keV/cm^2/s/sr. We also estimate analytically the extragalactic background due to Dark Matter annihilation, increasing the accuracy of the earlier computations. Indeed, we take into account the large positron escape fraction from low mass dark matter halos, unable to confine a dense and magnetized interstellar medium. Our new background estimate turns out to be one order of magnitude lower, so that the hypothesis of a light Dark Matter candidate remains compatible with the observed extragalactic background for a wider range of particle masses and cross-sections.

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arXiv2006

Constraints on Light Dark Matter From Core-Collapse Supernovae

We show that light ($\simeq$ 1 -- 30 MeV) dark matter particles can play a significant role in core-collapse supernovae, if they have relatively large annihilation and scattering cross sections, as compared to neutrinos. We find that if such particles are lighter than $\simeq$ 10 MeV and reproduce the observed dark matter relic density, supernovae would cool on a much longer time scale and would emit neutrinos with significantly smaller energies than in the standard scenario, in disagreement with observations. This constraint may be avoided, however, in certain situations for which the neutrino--dark matter scattering cross sections remain comparatively small.

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arXiv2005

Light Dark Matter

The SPI spectrometer aboard of the INTEGRAL satellite has released a map of the e+e- annihilation emission line of unprecedented quality, showing that most of the photons arise from a region coinciding with the stellar bulge of the Milky Way. The impressive intensity (10^-3 photon/cm^2/s) and morphology (round and wide) of the emission is begging an explanation. Different classes of astrophysical objects could inject positrons in the interstellar medium of the bulge, but the only acceptable ones should inject them at energies low enough to avoid excessive bremsstrahlung emission in the soft gamma ray regime. Among the ~ MeV injectors, none seems generous enough to sustain the high level of annihilation observed. Even the most profuse candidate, namely the beta+ radioactivity of 56 Co nuclei created and expelled in the interstellar medium by explosive nucleosynthesis of type Ia supernovae, falls short explaining the phenomenon due to the small fraction of positrons leaking out from the ejecta (3 %), together with the low SNIa rate in the bulge (0.03 per century). It is therefore worth exploring alternative solutions, as for instance, the idea that the source of the positrons is the annihilation of light dark matter (LDM) particles of the kind recently proposed, totally independently, by Boehm and Fayet. Assuming that LDM is the culprit, crucial constraints on the characteristics (mass and annihilation cross-section) of the associated particle may be discussed, combining direct gamma ray observations and models of the early Universe. In particular, the mass of the LDM particles should be significantly less than 100 MeV, so that the e+ and e- resulting from their annihilations do not radiate exceedingly through bremsstrahlung in the interstellar gas of the galactic bulge.

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arXiv2002

Constraining the strength of Dark Matter Interactions from Structure Formation

We discuss the damping of primordial dark matter fluctuations, taking into account explicitly the interactions of dark matter - whatever their intensity - both with itself and with other particle species. Relying on a general classification of dark matter particle candidates, our analysis provides, from structure formation, a new set of constraints on the dark matter particle mass and interaction rates (in particular with photons and neutrinos). This determines up to which cross sections the dark matter interactions may effectively be disregarded, and when they start playing an essential role, either through collisional damping or through an enhancement of the free-streaming scale. It leads us to extend the notions of Cold, Warm and Hot Dark Matter scenarios when dark matter interactions are no longer taken to be negligible. It also suggests the possibility of new scenarios of Collisional Warm Dark Matter, with moderate damping induced by dark matter interactions.

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arXiv2001

Equivalence Principle tests, Equivalence theorems and New long-range forces

We discuss the possible existence of new long-range forces mediated by spin-1 or spin-0 particles. By adding their effects to those of gravity, they could lead to apparent violations of the Equivalence Principle. While the vector part in the couplings of a new spin-1 U boson involves, in general, a combination of the B and L currents, there may also be, in addition, an axial part as well. If the new force has a finite range λ, its intensity is proportional to 1/(λ^2 F^2), F being the extra U(1) symmetry-breaking scale. Quite surprisingly, particle physics experiments can provide constraints on such a new force, even if it is extremely weak, the corresponding gauge coupling being extremely small (<< 10^-19 !). An ``equivalence theorem'' shows that a very light spin-1 U boson does not in general decouple even when its gauge coupling vanishes, but behaves as a quasimassless spin-0 particle, having pseudoscalar couplings proportional to 1/F. Similarly, in supersymmetric theories, a very light spin-3/2 gravitino might be detectable as a quasi massless spin-1/2 goldstino, despite the extreme smallness of Newton's gravitational constant G_N, provided the supersymmetry-breaking scale is not too large. Searches for such U bosons in ψand Υdecays restrict F to be larger than the electroweak scale (the U actually becoming, as an axion, quasi ``invisible'' in particle physics for sufficiently large F). This provides strong constraints on the corresponding new force and its associated EP violations. We also discuss briefly new spin-dependent forces.

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arXiv2001

About the origins of the Supersymmetric Standard Model

Could one use supersymmetry to relate the fermions, constituants of matter, with the bosons messengers of the interactions? This is, ideally, what a symmetry between fermions and bosons would be expected to do. However many obstacles seemed, long ago, to prevent supersymmetry from possibly being a fundamental symmetry of Nature. Which fermions and bosons could be related? Is spontaneous supersymmetry breaking possible at all? If yes, where is the corresponding spin-1/2 Goldstone fermion? Supersymmetric theories also involve Majorana fermions, unknown in Nature. And how could we define conserved quantum numbers like B and L, when these are carried by fundamental (Dirac) fermions only, not by bosons? An early attempt to relate the photon with a ``neutrino'' led us to R-invariance and to a new R quantum number carried by the supersymmetry generator, but this ``neutrino'' had to be reinterpreted as a new particle, the photino. We also had to introduce bosons carrying ``fermion numbers'' B and L, which became the squarks and sleptons. This led to the Supersymmetric Standard Model, involving SU(3) x SU(2) x U(1) gauge superfields interacting with chiral quark and lepton superfields, and two doublet Higgs superfields responsible for quark and lepton masses. R-parity, deeply related with B and L conservation laws, appeared as a remnant of the original R-invariance, reduced to a discrete symmetry so that the gravitino and gluinos can acquire masses. We also comment about supersymmetry breaking.

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arXiv2001

Equivalence Principle Tests and New Long-Range Forces

We discuss the possible existence of new long-range forces mediated by spin-1 or spin-0 particles. They would add their effects to those of gravity, and could lead to apparent violations of the Equivalence Principle. Informations on the (vector and axial) couplings of a new spin-1 U boson may be obtained from spontaneously broken gauge invariance. The charge associated with the vector coupling may be expressed as a linear combination of B and L. If the new force has a finite range lambda, its intensity turns out to be proportional to 1/(lambda^2 F^2), F being the extra U(1) symmetry-breaking scale. Quite surprisingly, particle physics experiments can provide constraints on such a force, even if the corresponding gauge coupling is extremely small (<< 10^-19 !). An "equivalence theorem" shows that a very light spin-1 U boson with non-vanishing axial couplings does not in general decouple even when its gauge coupling vanishes, but behaves as a quasimassless pseudoscalar. (This equivalence theorem is similar to the one of supersymmetry/supergravity theories, according to which a very light spin-3/2 gravitino might get detectable as a quasi massless spin-1/2 goldstino, despite the extreme smallness of Newton's gravitational constant G_N.) Searches for the radiative production of such U bosons in psi and upsilon decays restrict the extra U(1) symmetry-breaking scale F to be larger than the electroweak scale, providing constraints on the intensity of the corresponding new force.

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arXiv2001

About Superpartners and the Origins of the Supersymmetric Standard Model

We recall the obstacles which seemed, long ago, to prevent supersymmetry from possibly being a fundamental symmetry of Nature. Which bosons and fermions could be related? Is spontaneous supersymmetry breaking possible? Where is the spin-1/2 Goldstone fermion of supersymmetry? Can one define conserved baryon and lepton numbers in such theories, although they systematically involve self-conjugate Majorana fermions? etc.. We then recall how an early attempt to relate the photon with a ``neutrino'' led to the definition of R-invariance, but that this ``neutrino'' had to be reinterpreted as a new particle, the photino. This led us to the Supersymmetric Standard Model, involving the SU(3) x SU(2) x U(1) gauge interactions of chiral quark and lepton superfields, and of two doublet Higgs superfields responsible for the electroweak breaking and the generation of quark and lepton masses. The original continuous R-invariance was then abandoned in favor of its discrete version, R-parity -- reexpressed as (-1)^2S (-1)^(3B+L) -- so that the gravitino and gluinos can acquire masses. We also comment about supersymmetry breaking.

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arXiv1999

About R-parity and the Supersymmetric Standard Model

We recall the obstacles which seemed, long ago, to prevent one from viewing supersymmetry as a possible fundamental symmetry of Nature. Is spontaneous supersymmetry breaking possible ? Where is the spin-1/2 Goldstone fermion of supersymmetry, if not a neutrino ? Which bosons and fermions could be related ? Can one define conserved baryon and lepton numbers in such theories, although they systematically involve self-conjugate Majorana fermions ? If we have to postulate the existence of new bosons carrying B and L (the new spin-0 squarks and sleptons), can we prevent them from mediating new unwanted interactions ? We then recall how we obtained the three basic ingredients of the Supersymmetric Standard Model: 1) the SU(3) x SU(2) x U(1) gauge superfields; 2) the chiral quark and lepton superfields; 3) the two doublet Higgs superfields responsible for the electroweak breaking, and the generation of quark and lepton masses. The original continuous ``R-invariance'' of this model was soon abandoned in favor of its discrete version, R-parity, so that the gravitino, and gluinos, can acquire masses - gluinos getting their masses from supergravity, or radiative corrections. R-parity forbids unwanted squark and slepton exchanges, and guarantees the stability of the ``lightest supersymmetric particle''. It is present only since we restricted the initial superpotential to be an even function of quark and lepton superfields (so as to allow for B and L conservation laws), as made apparent by the formula re-expressing R-parity as (-1)^2S (-1)^(3B+L). Whether it turns out to be absolutely conserved, or not, R-parity plays an essential role in the phenomenology of supersymmetric theories, and the experimental searches for the new sparticles.

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