arXiv subjects

M. Plumacher

Publications and source records attributed to M. Plumacher.

16 recordsLinked to original sources

arXiv2009

Full Boltzmann equations for leptogenesis including scattering

We study the evolution of a cosmological baryon asymmetry produced via leptogenesis by means of the full classical Boltzmann equations, without the assumption of kinetic equilibrium and including all quantum statistical factors. Beginning with the full mode equations we derive the usual equations of motion for the right-handed neutrino number density and integrated lepton asymmetry, and show explicitly the impact of each assumption on these quantities. For the first time, we investigate also the effects of scattering of the right-handed neutrino with the top quark to leading order in the Yukawa couplings by means of the full Boltzmann equations. We find that in our full Boltzmann treatment the final lepton asymmetry can be suppressed by as much as a factor of 1.5 in the weak wash-out regime (K<1), compared to the usual integrated approach which assumes kinetic equilibrium and neglects quantum statistics. This suppression is in contrast with the enhancement seen in some previous studies that considered only decay and inverse decay of the right-handed neutrino. However, this suppression quickly decreases as we increase K. In the strong wash-out regime (K>1), the full Boltzmann treatment and the integrated approach give nearly identical final lepton asymmetries (within 10 % of each other at K>3). Finally, we show that the opposing effects of quantum statistics on decays/inverse decays and the scattering processes tend to reduce the net importance of scattering on leptogenesis in the full treatment compared to the integrated approach.

hep-ph↗

arXiv2008

Effects of reheating on leptogenesis

We study the evolution of a cosmological baryon asymmetry in leptogenesis when the right-handed neutrinos are produced in inflaton decays. By performing a detailed numerical study over a broad range of inflaton-neutrino couplings we show that the resulting asymmetry can be larger by two orders of magnitude or more than in thermal leptogenesis, if the reheating temperature T_{RH} is of the same order as the right-handed neutrino mass M_1. Hence, the lower limit on the baryogenesis temperature obtained in thermal leptogenesis can be relaxed accordingly.

hep-ph↗

arXiv2007

Cosmic Microwave Background, Matter-Antimatter Asymmetry and Neutrino Masses

We study the implications of thermal leptogenesis for neutrino parameters. Assuming that decays of N_1, the lightest of the heavy Majorana neutrinos, initiate baryogenesis, we show that the final baryon asymmetry is determined by only four parameters: the CP asymmetry epsilon_1, the heavy neutrino mass M_1, the effective light neutrino mass \tilde{m}_1, and the quadratic mean \bar{m} of the light neutrino masses. Imposing the CMB measurement of the baryon asymmetry as constraint on the neutrino parameters, we show, in a model independent way, that quasi-degenerate neutrinos are incompatible with thermal leptogenesis. For maximal CP asymmetry epsilon_1, and neutrino masses in the range from (Δm^2_{sol})^{1/2} to (Δm^2_{atm})^{1/2}, the baryogenesis temperature is T_B = O(10^{10}) GeV.

hep-ph↗

arXiv2005

The CP-asymmetry in resonant leptogenesis

We study the resonantly enhanced CP-asymmetry in the decays of nearly mass-degenerate heavy right-handed Majorana neutrinos for which different formulae have been presented in the literature, depending on the method used to calculate it. We consider two different techniques and show that they lead to the same result, thereby reconciling the different approaches.

hep-ph↗

arXiv2004

Some Aspects of Thermal Leptogenesis

Properties of neutrinos may be the origin of the matter-antimatter asymmetry of the universe. In the seesaw model for neutrino masses this leads to important constraints on the properties of light and heavy neutrinos. In particular, an upper bound on the light neutrino masses of 0.1 eV can be derived. We review the present status of thermal leptogenesis with emphasis on the theoretical uncertainties and discuss some implications for lepton and quark mass hierarchies, CP violation and dark matter. We also comment on the `leptogenesis conspiracy', the remarkable fact that neutrino masses may lie in the range where leptogenesis works best.

hep-ph↗

arXiv2004

Leptogenesis for Pedestrians

During the process of thermal leptogenesis temperature decreases by about one order of magnitude while the baryon asymmetry is generated. We present an analytical description of this process so that the dependence on the neutrino mass parameters becomes transparent. In the case of maximal CP asymmetry all decay and scattering rates in the plasma are determined by the mass M_1 of the decaying heavy Majorana neutrino, the effective light neutrino mass tilde{m}_1 and the absolute mass scale bar{m} of the light neutrinos. In the mass range suggested by neutrino oscillations, m_{sol} \simeq 8*10^{-3} eV \lesssim \tilde{m}_1 \lesssim m_{atm} \simeq 5*10^{-2} eV, leptogenesis is dominated just by decays and inverse decays. The effect of all other scattering processes lies within the theoretical uncertainty of present calculations. The final baryon asymmetry is dominantly produced at a temperature T_B which can be about one order of magnitude below the heavy neutrino mass M_1. We also derive an analytical expression for the upper bound on the light neutrino masses implied by successful leptogenesis.

hep-ph↗

arXiv2003

The Neutrino Mass Window for Baryogenesis

Interactions of heavy Majorana neutrinos in the thermal phase of the early universe may be the origin of the cosmological matter-antimatter asymmetry. This mechanism of baryogenesis implies stringent constraints on light and heavy Majorana neutrino masses. We derive an improved upper bound on the CP asymmetry in heavy neutrino decays which, together with the kinetic equations, yields an upper bound on all light neutrino masses of 0.1 eV. Lepton number changing processes at temperatures above the temperature T_B of baryogenesis can erase other, pre-existing contributions to the baryon asymmetry. We find that these washout processes become very efficient if the effective neutrino mass \tilde{m}_1 is larger than m_* \simeq 10^{-3} eV. All memory of the initial conditions is then erased. Hence, for neutrino masses in the range from (Δm^2_sol)^{1/2} \simeq 8*10^{-3} eV to (Δm^2_atm)^{1/2} \simeq 5*10^{-2} eV, which is suggested by neutrino oscillations, leptogenesis emerges as the unique source of the cosmological matter-antimatter asymmetry.

hep-ph↗

arXiv2001

Remarks on the high-energy behaviour of cross-sections in weak-scale string theories

We consider the high-energy behaviour of processes involving Kaluza-Klein (KK) gravitons of weak-scale string theories. We discuss how form-factors derived within string theory modify the couplings of KK gravitons and thereby lead to an exponential fall-off of cross sections in the high-energy limit. Further, we point out that the assumption of Regge behaviour for a scattering amplitude in the high energy limit, $T\propto s^{α(t)}$, combined with a linear growth of the total cross-section, $σ_{tot}(s)\propto s$, violates elastic unitarity. Regge behaviour leads to a stringent bound on the growth of the total cross-section, $\stot (s) \leq 32πα' \ln(s/s_0)$.

hep-ph↗

arXiv2000

Ultrahigh energy neutrino interactions and weak-scale string theories

It has been suggested that ultrahigh energy neutrinos can acquire cross-sections approaching hadronic size if the string scale is as low as 1-10 TeV. In this case, the vertical air showers observed with energies above the Greisen-Zatsepin-Kuzmin cutoff at E approximately 6x10^{19} eV could be initiated by neutrinos which are the only known primaries able to travel long distances unimpeded. We have calculated the neutrino-nucleon cross-section due to the exchange of Kaluza-Klein excitations of the graviton in a field theoretical framework. We have found that the neutrino-nucleon cross section and the transferred energy per interaction are too small to explain vertical showers even in the most optimistic scenario.

astro-ph↗

arXiv1999

Matter Antimatter Asymmetry and Neutrino Properties

The cosmological baryon asymmetry can be explained as remnant of heavy Majorana neutrino decays in the early universe. We study this mechanism for two models of neutrino masses with a large ν_μ-ν_τmixing angle which are based on the symmetries SU(5) x U(1)_F and SU(3)_c x SU(3)_L x SU(3)_R x U(1)_F, respectively. In both cases B-L is broken at the unification scale Λ_{GUT}. The models make different predictions for the baryogenesis temperature and the gravitino abundance.

hep-ph↗

arXiv1998

Baryon Asymmetry, Lepton Mixing and SO(10) Unification

Baryogenesis appears to require lepton number violation. This is naturally realized in extensions of the standard model containing right-handed neutrinos. We discuss the generation of a baryon asymmetry by the out-of-equilibrium decay of heavy Majorana neutrinos in these models, without and with supersymmetry. All relevant lepton number violating scattering processes which can inhibit the generation of an asymmetry are taken into account. We assume a similar pattern of mixings and masses for neutrinos and up-type quarks, as suggested by SO(10) unification. This implies that B-L is broken at the unification scale Λ_{GUT}\sim 10^{16} GeV, if m_{ν_μ} \sim 3\cdot10^{-3} eV, as preferred by the MSW solution to the solar neutrino deficit. The observed baryon asymmetry is then obtained without any fine tuning of parameters.

hep-ph↗

arXiv1998

Baryon Asymmetry, Neutrino Mixing and Supersymmetric SO(10) Unification

The baryon asymmetry of the universe can be explained by the out-of-equilibrium decays of heavy right-handed neutrinos. We analyse this mechanism in the framework of a supersymmetric extension of the Standard Model and show that lepton number violating scatterings are indispensable for baryogenesis, even though they may wash-out a generated asymmetry. By assuming a similar pattern of mixings and masses for neutrinos and up-type quarks, as suggested by SO(10) unification, we can generate the observed baryon asymmetry without any fine tuning, if (B-L) is broken at the unification scale Λ_{GUT}\sim 10^{16} GeV and, if m_{ν_μ} \sim 3\cdot 10^{-3} eV as preferred by the MSW solution to the solar neutrino deficit.

hep-ph↗

arXiv1998

Baryon Asymmetry, Neutrino Mixing and Supersymmetric SO(10) Unification

The baryon asymmetry of the universe can be explained by the out-of-equilibrium decays of heavy right-handed neutrinos. We analyse this mechanism in the framework of a supersymmetric extension of the Standard Model and show that lepton number violating scatterings are indispensable for baryogenesis, even though they may wash-out a generated asymmetry. By assuming a similar pattern of mixings and masses for neutrinos and up-type quarks, as suggested by SO(10) unification, we can generate the observed baryon asymmetry without any fine tuning, if $(B-L)$ is broken at the unification scale $Λ_{GUT}\sim 10^{16} $GeV and, if $m_{\n_\m} \sim 3\cdot 10^{-3} $eV as preferred by the MSW solution to the solar neutrino deficit.

hep-ph↗

arXiv1998

CP Asymmetry in Majorana Neutrino Decays

We study CP asymmetries in lepton-number violating two-body scattering processes and show how they are related to CP asymmetries in the decays of intermediate massive Majorana neutrinos. Self-energy corrections, which do not contribute to CP asymmetries in two-body processes, induce CP violating couplings of the intermediate Majorana neutrinos to lepton-Higgs states. We briefly comment on the implications of these results for applications at finite temperature.

hep-ph↗

arXiv1997

Baryon Asymmetry of the Universe and Lepton Mixing

Baryogenesis appears to require lepton number violation. This is naturally realized in extensions of the standard model containing right-handed neutrinos. We discuss the generation of a baryon asymmetry by the out-of-equilibrium decay of heavy Majorana neutrinos in these models, without and with supersymmetry. All relevant lepton number violating scattering processes which can inhibit the generation of an asymmetry are taken into account. We assume a similar pattern of mixings and masses for neutrinos and up-type quarks, as suggested by SO(10) unification. This implies that B-L is broken at the unification scale $Λ_{GUT}\sim 10^{16}$ GeV, if $m_{ν_μ} \sim 3\cdot10^{-3}$ eV, as preferred by the MSW solution to the solar neutrino deficit. The observed baryon asymmetry is then obtained without any fine tuning of parameters.

hep-ph↗

arXiv1996

Baryon Asymmetry and Neutrino Mixing

In theories where $B-L$ is a spontaneously broken local symmetry, the cosmological baryon asymmetry can be generated by the out-of-equilibrium decay of heavy Majorana neutrinos. We study this mechanism assuming a similar pattern of mixings and masses for leptons and quarks, as suggested by SO(10) unification. This implies that $B-L$ is broken at the unification scale $Λ_{\mbox{\scriptsize GUT}}\sim 10^{16}$ GeV, if $m_{\n_\m} \sim 3\cdot 10^{-3}$eV as preferred by the MSW explanation of the solar neutrino deficit. The observed value of the baryon asymmetry, $n_B/s \sim 10^{-10}$, is then obtained without any fine tuning of parameters.

hep-ph↗