arXiv subjects

Manuel Drees

Publications and source records attributed to Manuel Drees.

At least 91 records · Page 5Linked to original sources

arXiv2005

Neutralino Dark Matter in mSUGRA: reopening the light Higgs pole window

The requirement that the lightest neutralino $\tildeχ_1^0$ has the right thermal relic density to explain all Dark Matter in the universe strongly constrains the parameter space of supersymmetric models in general, and of the mSUGRA model in particular. Recently improved calculations of the mass of the light CP-even Higgs boson $h$ present in this model, and the increased central value of the mass of the top quark, have re--opened the possibility that $2 \mlsp \lsim m_h$. In this ``$h-$pole region'' the LSP annihilation cross section is enhanced by near-resonant $h$ exchange in the $s-$channel, reducing the relic density to acceptable values. We delineate the corresponding region of mSUGRA parameter space, and explore its phenomenology. In particular, we find strong upper bounds on the masses of the gluino, lighter chargino and LSP.

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arXiv2005

Some Comments on "Split" Supersymmetry

An argument against tolerating finetuning in the Higgs sector is presented, by emphasizing the difference between (well understood) quantum corrections to scalar masses and the (unsolved) problem of the cosmological constant. I also point out that ``split'' supersymmetry, where all scalars except one Higgs boson have masses many orders of magnitude above the weak scale, is not compatible with simple mechanisms of transmitting supersymmetry breaking (gravity, gauge or anomaly mediation), unless a second, independent finetuning of parameters is introduced. This finetuning is required to obtain an acceptable ratio of vacuum expectation values tan(beta).

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arXiv2004

Leptogenesis as the source of gravitino dark matter and density perturbations

We investigate the possibility that the entropy producing decay of a right-handed sneutrino condensate can simultaneously be the source of the baryon asymmetry, of gravitino dark matter, and of cosmological density perturbations. For generic values of soft supersymmetry breaking terms in the visible sector of 1-10 TeV, condensate decay can yield the dark matter abundance for gravitinos in the mass range 1 MeV to 1 TeV, provided that the resulting reheat temperature is below $10^6$ GeV. The abundance of thermally produced gravitinos before and after sneutrino decay is then negligible. We consider different leptogenesis mechanisms to generate a sufficient asymmetry, and find that low-scale soft leptogenesis works most naturally at such temperatures. The condensate can easily generate sufficient density perturbations if its initial amplitude is $\sim {\cal O}(M_{\rm GUT})$, for a Hubble expansion rate during inflation $> 10^9$ GeV. Right-handed sneutrinos may therefore at the same time provide a source for baryogenesis, dark matter and the seed of structure formation.

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arXiv2004

Supersymmetric Dark Matter 2004

Recent cosmological data allow to determine the universal Dark Matter (DM) density to a precision of about 10%, if a simple, well-motivated ansatz for the spectrum of primordial density perturbations is correct. Not surprisingly, a thermal neutralino χwill have the correct relic density only in ``small'' regions of parameter space. In particular, for fixed values of the other parameters, the allowed region in the (m_0, m_{1/2} plane (in mSUGRA or similar models) seems quite small, if standard assumptions about the Universe at temperature T \simeq m_χ/ 10 are correct. I argue that the allowed parameter space is actually still quite large, when all uncertainties are properly taken into account. In particular, the current lower limits on sparticle and Higgs masses that can be derived within mSUGRA do not change appreciably when the DM relic density constraint is imposed. I also show that deviating from mSUGRA does not alleviate the finetuning required to obtain the correct relic density, unless one also postulates a non-standard cosmology. Finally, I briefly discuss claimed positive evidence for particle Dark Matter.

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arXiv2004

Systematic study of the impact of CP-violating phases of the MSSM on leptonic high-energy observables

Low-energy results from measurements of leptonic dipole moments are used to derive constraints on the CP-violating phases of the dimensionful parameters of the minimal supersymmetric extension of the standard model (MSSM). We use these (known) bounds to investigate the impact of these phases on CP-even cross sections at high-energy e^+e^- and e^-e^- colliders. To that end we define two measures of the significance with which the existence of non--vanishing phases could be deduced from the measurements of these cross sections. We find that highly significant evidence for deviations from the CP-conserving MSSM could be obtained at the next e^+e^- collider even if the electric dipole moment of the electron is very small or zero. We also analyze a CP-odd final state polarization, which can be large when two different charginos or neutralinos are produced. Finally, we study correlations between the phase--sensitive observables.

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arXiv2004

Leptogenesis from a sneutrino condensate revisited

We re--examine leptogenesis from a right--handed sneutrino condensate, paying special attention to the $B-$term associated with the see--saw Majorana mass. This term generates a lepton asymmetry in the condensate whose time average vanishes. However, a net asymmetry will result if the sneutrino lifetime is not much longer than the period of oscillations. Supersymmetry breaking by thermal effects then yields a lepton asymmetry in the standard model sector after the condensate decays. We explore different possibilities by taking account of both the low--energy and Hubble $B-$terms. It will be shown that the desired baryon asymmetry of the Universe can be obtained for a wide range of Majorana mass.

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arXiv2003

The Top--Down Interpretation of Ultra--High Energy Cosmic Rays

The origin of Ultra--High Energy ($E \gsim 10^{20}$ eV) Cosmic Rays (UHECR) remains mysterious. I discuss ``top--down'' models, where UHECR originate from the decay of very massive, long--lived particles. I summarize the calculation of the spectrum of decay products, discuss possible problems with this scenario, and describe ways to test it by searching for very energetic neutrinos and neutralinos.

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arXiv2003

Complete 1-Loop Calculation of the T-violating D-Parameter in Neutron Decay in the MSSM

We investigate the violation of time reversal invariance in the decay of the free neutron in the framework of the Minimal Supersymmetric Standard Model (MSSM). The coefficient of the triple product of the neutron spin and the momenta of electron and neutrino, the so called D parameter, is computed at one loop order including all diagrams. We find that D is mainly sensitive to the trilinear A coupling in the squark sector and to the phase of the coefficient μwhich mixes the two Higgs superfields. The maximal MSSM contribution using parameters still allowed by experiment is however at D \approx 10^{-7}, while QED final state interactions give a value of D_{fsi} = - 2.3 * 10^{-5}. Explicit expressions for all relevant diagrams are given in an Appendix.

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arXiv2003

Particle Physics Explanations for Ultra High Energy Cosmic Ray Events

The origin of cosmic ray events with $E \gsim 10^{11}$ GeV remains mysterious. In this talk I briefly summarize several proposed particle physics explanations: a breakdown of Lorentz invariance, the ``$Z-$burst'' scenario, new hadrons with masses of several GeV as primaries, and magnetic monopoles with mass below $10^{10}$ GeV as primaries. I then describe in a little more detail the idea that these events are due to the decays of very massive, long--lived exotic particles.

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arXiv2003

Detailed analysis of the decay spectrum of a super-heavy X particle

Decays of superheavy X particles with mass M_X ~ 10^12 - 10^16 GeV have been proposed as origin of the observed ultra high energy cosmic rays (UHECR). We describe in detail the physics involved in the different steps of the decay of such a particle. In particular, we give for the first time the complete set of splitting functions needed to model a parton shower in the minimal supersymmetric extension of the Standard Model (MSSM). We present our results in the form of fragmentation functions of any (s)particle of the MSSM into any final stable particle (proton, photon, electron, three types of neutrino, lightest superparticle LSP) at a virtuality Q = M_X, over a scaled energy range x = 2E/M_X in [10^{-13}, 1]. Extending the coverage to such small fractional energies is necessary since the energy region around 10^18 eV and below could be of considerable interest in testing this kind of model for generating UHECR. We explicitly demonstrate that our treatment conserves energy, and discuss the dependence of the final result on SUSY parameters. We also show that our results are essentially independent of the necessary extrapolation of the input fragmentation functions, which are known only for x >= 0.1, towards small x. Finally, we added a new treatment of the color coherence effects at very small x, using the analytic ``MLLA'' solution. Our computer code will soon be made available.

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arXiv2002

Heavy particle production during reheating

We discuss production of heavy partciles during reheating. We find that the very energetic inflaton decay products can contribute to the production of massive stable particles, either through collisions with the thermal plasma, or through collisions with each other. If such reactions exist, the same massive particles can also be produced directly in inflaton decay, once higher--order processes are included. We show that these new, non--thermal production mechanisms often significantly strengthen constraints on the parameters of models containing massive stable particles.

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arXiv2002

Astroparticle Physics and Colliders

In this talk I discuss the interplay between collider physics and four topics of astro-particle physics: neutrino oscillations, electroweak baryogenesis, LSP Dark Matter, and ultra-high energy cosmic rays (UHECR). Some astrophysical scenarios can (only) be tested decisively at colliders. In other cases input from collider experiments is required to sharpen predictions for future astro--particle physics experiments, e.g. for the LSP detection rate or the UHECR spectrum in top--down models.

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arXiv2002

Thermalization after inflation and production of massive stable particles

We discuss thermalization through perturbative inflaton decay at the end of inflation. We find that a thermal plasma should form well before all inflatons have decayed, unless all gauge symmetries are badly broken during that epoch. However, before they thermalize, the very energetic inflaton decay products can contribute to the production of massive stable particles, either through collisions with the thermal plasma, or through collisions with each other. If such reactions exist, the same massive particles can also be produced directly in inflaton decay, once higher--order processes are included. We show that these new, non--thermal production mechanisms often significantly strengthen constraints on the parameters of models containing massive stable particles; for example, stable charged particles with mass below the inflaton mass seem to be essentially excluded.

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arXiv2002

Production of massive stable particles in inflaton decay

We point out that inflaton decays can be a copious source of stable or long--lived particles $χ$ with mass exceeding the reheat temperature $T_R$. Once higher order processes are included, this statement is true for any $χ$ particle with renormalizable (gauge or Yukawa) interactions. This contribution to the $χ$ density often exceeds the contribution from thermal $χ$ production, leading to significantly stronger constraints on model parameters than those resulting from thermal $χ$ production alone. For example, we all but exclude models containing stable charged particles with mass less than half the mass of the inflaton.

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arXiv2002

Supersymmetric Higgs Boson Decays in the MSSM with Explicit CP Violation

Decays into neutralinos and charginos are among the most accessible supersymmetric decay modes of Higgs particles in most supersymmetric extensions of the Standard Model. In the presence of explicitly CP--violating phases in the soft breaking sector of the theory, the couplings of Higgs bosons to charginos and neutralinos are in general complex. Based on a specific benchmark scenario of CP violation, we analyze the phenomenological impact of explicit CP violation in the Minimal Supersymmetric Standard Model on these Higgs boson decays. The presence of CP--violating phases could be confirmed either directly through the measurement of a CP--odd polarization asymmetry of the produced charginos and neutralinos, or through the dependence of CP--even quantities (branching ratios and masses) on these phases.

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arXiv2002

Production of ultra-energetic cosmic rays through the decay of super-heavy X particles

We present a new and complete numerical analysis of the decay of super-heavy X particles, assumed to be the origin of cosmic rays with energy beyond the GZK cut-off. The decay of X initiates a ``parton shower'', where we include all degrees of freedom contained in the Minimal Supersymmetric Standard Model (MSSM). Since at energies near $M_X$ all gauge couplings are of similar magnitude, we include all of them, as well as third generation Yukawa couplings. Technically the shower development is described through the DGLAP evolution of the relevant fragmentation functions (FFs). We also carefully treat the decay of the superparticles as well as heavy SM particles created in the shower. Nonperturbative physics is parameterized through the input values of the FFs, which we take from the literature. The final result is the the complete spectrum of all stable particles at the very end of the shower : protons, electrons, neutrinos, photons and neutralinos, for an energy range from $10^{-7} M_X$ to $M_X$. In particular, the flux of high-energy neutralinos is sizable ; it might serve as ``smoking gun'' signature for this kind of scenario.

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arXiv2001

Constraints on mSUGRA and SUSY particle production at future $e^+e^-$ linear colliders

We perform a complete analysis of the supersymmetric particle spectrum in the Minimal Supergravity (mSUGRA) model. We show that present constraints on the Higgs boson and superparticle masses from collider searches and precision measurements still allow for large regions of the mSUGRA parameter space where some sparticles as well as the heavier Higgs particles, are light enough to be produced at the next generation of $e^+e^-$ linear colliders. An important part of this parameter space remains even when we require that the density of the lightest neutralinos left over from the Big Bang falls in the range favored by current determinations of the Dark Matter density in the Universe.

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arXiv2001

Neutrino Mass Operator Renormalization in Two Higgs Doublet Models and the MSSM

In a recent re-analysis of the Standard Model (SM) beta-function for the effective neutrino mass operator, we found that the previous results were not entirely correct. Therefore, we consider the analogous dimension five operators in a class of Two Higgs Doublet Models (2HDM's) and the Minimal Supersymmetric Standard Model (MSSM). Deriving the renormalization group equations for these effective operators, we confirm the existing result in the case of the MSSM. Some of our 2HDM results are new, while others differ from earlier calculations. This leads to modifications in the renormalization group evolution of leptonic mixing angles and CP phases in the 2HDM's.

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