arXiv subjects

Karim Benakli

Publications and source records attributed to Karim Benakli.

65 records · Page 4Linked to original sources

arXiv1999

Phenomenology of Low Quantum Gravity Scale Models

We study some phenomenological implications of models where the scale of quantum gravity effects lies much below the four-dimensional Planck scale. These models arise from M-theory vacua where either the internal space volume is large or the string coupling is very small. We provide a critical analysis of ways to unify electroweak, strong and gravitational interactions in M-theory. We discuss the relations between different scales in two M-vacua: Type I strings and Ho\v rava-Witten supergravity models. The latter allows possibilities for an eleven-dimensional scale at TeV energies with one large dimension below separating our four-dimensional world from a hidden one. Different mechanisms for breaking supersymmetry (gravity mediated, gauge mediated and Scherk-Schwarz mechanisms) are discussed in this framework. Some phenomenological issues such as dark matter (with masses that may vary in time), origin of neutrino masses and axion scale are discussed. We suggest that these are indications that the string scale may be lying in the $10^{10} - 10^{14}$ GeV region.

hep-ph↗

arXiv1998

Baryogenesis in Models with a Low Quantum Gravity Scale

We make generic remarks about baryogenesis in models where the scale $M_s$ of quantum gravity is much below the Planck scale. These correspond to M-theory vacua with a large volume for the internal space. Baryogenesis is a challenge, particularly for $M_s \lappeq 10^5$ GeV, because there is an upper bound on the reheat temperature of the Universe, and because certain baryon number violating operators must be suppressed. We discuss these constraints for different values of $M_s$, and illustrate with a toy model the possibility of using horizontal family symmetries to circumvent them.

hep-ph↗

arXiv1998

Scales and Cosmological Applications of M Theory

I review recent results in three topics of the M-world: (i) Scales. (ii) New dark matter candidates. (iii) Cosmological solutions from p-branes. The three topics are discussed in the framework of Hořava-Witten compactifications. Part (iii) includes comments on cosmological solutions in M-theory describing nucleation of universes through instanton effects and expansions toward asymptotically flat or anti-de-Sitter spaces.

hep-th↗

arXiv1998

Heterotic String Theory on Anti-de-Sitter Spaces

We suggest that compactifications on Anti-de-Sitter (AdS) spaces of type IIA, IIB, heterotic strings and eleven dimensional vacuua of M-theory are related by a combination of $T$ and strong/weak dualities. Maldacena conjecture relates then all these vacuua to a conformal theory on the boundaries. Furthermore acting with discrete groups on part of the internal spaces of these theories will lead to further dual theories with less or no supersymmetry.

hep-th↗

arXiv1998

Cosmological Solution in M-theory on S^1/Z_2

We provide the first example of a cosmological solution of the Horava-Witten supergravity. This solution is obtained by exchanging the role of time with the radial coordinate of the transverse space to the five-brane soliton. On the boundary this corresponds to rotating an instanton solution into a tunneling process in a space with Lorentzian signature, leading to an expanding universe. Due to the freedom to choose different non-trivial Yang-Mills backgrounds on the boundaries, the two walls of the universe ( visible and hidden worlds) expand differently. However at late times the anisotropy is washed away by gravitational interactions.

hep-th↗

arXiv1998

Natural Candidates for Superheavy Dark Matter in String and M Theory

We reconsider superheavy dark matter candidates in string and M theory, in view of the possibility that inflation might generate superheavy particles with an abundance close to that required for a near-critical Universe. We argue that cryptons - stable or metastable bound states of matter in the hidden sector - are favoured over other possible candidates in string or $M$ theory, such as the Kaluza-Klein states associated with extra dimensions. We exhibit a specific string model that predicts cryptons as hidden-sector bound states weighing $\sim 10^{12}$ GeV, and discuss their astrophysical observability.

hep-ph↗

arXiv1998

Modulino as natural candidate for a sterile neutrino

We discuss the possible generation of R-parity violating bilinear terms $ μ_i\bar L_i H_2$ in both cases of gravity and gauge mediated supersymmetry breaking. Some phenomenological aspects are reviewed. In particular for scenario where $ μ_i$ depend on the vacuum expectation values of some fields $S$, its fermionic partner $\tilde S$ plays the role of a sterile neutrino. This situation is quiet generic in the case of models arising from M-theory where $S$ is a modulus field. Observable effects are expected to be seen if the mass and mixing of $\tilde S$ with active neutrinos lie in an interesting region of parameters. This is naturally the case in gauge mediated supersymmetry breaking and some class of no-scale supergravity models where the gravitino mass is very small. For models with gravitino mass $m_{3/2}\sim$ TeV, we discuss the possibility that the modulino mass is of the order of $m^2_{3/2}/M_{Pl}$.

hep-ph↗

arXiv1997

Neutrino - Modulino Mixing

We suggest the existence of a light singlet fermion, $S$, which interacts with observable matter only via a Planck mass suppressed interaction: $\sim m_{3/2}/M_P$, where $m_{3/2}$ is the supergravity gravitino mass. If the mass of the singlet equals $\sim m_{3/2}^2/M_P$, then $ν_e \to S$ resonance conversion solves the solar neutrino problem or leads to observable effects. The $νS$-mixing changes supernova neutrino fluxes and has an impact on the primordial nucleosynthesis. The singlet $S$ can originate as the supersymmetric partner of the moduli fields in supergravity or low energy effective theory steaming from superstrings. The $νS$-mixing may be accompanied by observable R-parity breaking effects.

hep-ph↗

arXiv1995

Supersymmetry Breaking In Orbifolds Compactifications

Known mechanisms for breaking of supersymmetry at the level of string theory imply that at least one of the internal dimensions has a very large size. Experimental detection of the associated light Kaluza-Klein (KK) excitations would be a strong hint for the existence of string like elementary objects, as no consistent field theory describing them is known. We restrict the discussion to the Scherk-Schwarz mechanism in orbifold compactifications. For this case we investigate the quantum number of the lightest predicted KK states.

hep-th↗

arXiv1995

Perturbative Supersymmetry Breaking In Orbifolds With Wilson Line Backgrounds

A way to break supersymmetry in perturbative superstring theory is the string version of the Scherk-Schwarz mechanism. There, the fermions and bosons have mass splitting due to different compactification boundary conditions. We consider the implementation of this mechanism in abelian orbifold compactifications with Wilson line backgrounds. For $Z_N$ and $Z_N\times Z_M$ orbifolds, we give the possible $U(1)$ R-symmetries which determine the mass splitting, and thus, the supersymmetry breaking at the perturbative level. The phenomenlogical viability of this mechanism implies some dimension(s) to be as large as the TeV scale. We explain how the lighter Kaluza-Klein states associated with the extra-dimension(s) have quantum numbers depending on the Wilson lines used.

hep-th↗

arXiv1995

Stringy Unification Helps See-Saw Mechanism

In this paper we explore the possibility of intermediate scale physics in the context of superstring models with {\it higher Kac-Moody levels}, by focusing on left-right and Pati-Salam symmetries. We find that the left-right scale may lie in the range $10^{10} - 10^{12}$ GeV which is favored by neutrino physics, while the Pati-Salam scale is at most two or three orders of magnitude below the unification scale $M_X$. We also show that the scale of $B-L$ breaking can be as low as 1 TeV or so, providing protection against too rapid proton decay in supersymmetry. Our results allow a natural value for the scale $M_X \sim 10^{18}$ GeV and the agreement with the experiment requires the value of $\sin^2 {θ_w}$ at $M_X$ to be in general very different from the usually assumed $3/8$.

hep-ph↗