arXiv subjects

Valerie Domcke

Publications and source records attributed to Valerie Domcke.

At least 73 records · Page 4Linked to original sources

arXiv2018

Gauge Field and Fermion Production during Axion Inflation

We study the dual production of helical Abelian gauge fields and chiral fermions through the Chern-Simons (CS) coupling with a pseudo-scalar inflaton in the presence of a chiral anomaly. Through the CS term, the motion of the inflaton induces a tachyonic instability for one of the two helicities of the gauge field. We show that the resulting helical gauge field necessarily leads to the production of chiral fermions by deforming their Fermi sphere into discrete Landau levels. The population of the lowest Landau level leads to a chiral asymmetry as inferred from the chiral anomaly, while the higher levels are populated symmetrically through pair production. From the backreaction of the fermions on the gauge field production we derive a conservative but stringent upper bound on the magnitude of the gauge fields. Consequently, we find that the scalar perturbations sourced by these helical gauge fields, responsible for enhanced structure formation on small scales, get reduced significantly. We also discuss the fate of the primordial chiral asymmetry and of the helical gauge fields after inflation, and show that the instability in the chiral plasma tends to erase these primordial asymmetries. This result may impact scenarios where the baryon asymmetry of the Universe is connected to primordial magnetic fields.

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arXiv2018

Freeze-in leptogenesis with 3 right-handed neutrinos

We provide the first systematic study of the viable parameter space for leptogenesis in the type-I seesaw model with three right-handed neutrinos whose Majorana masses lie below the electroweak scale. We highlight the very rich phenomenology of this scenario and discuss several mechanisms that can help to enhance the baryon asymmetry of the Universe. This allows for much larger heavy neutrino mixing angles than in the minimal scenario with two heavy neutrinos, resulting in solutions that can be probed with the LHC and other experiments. The light neutrino masses can be protected from radiative corrections by an approximate symmetry related to generalised lepton number.

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arXiv2018

Primordial gravitational waves for universality classes of pseudoscalar inflation

Current bounds from the polarization of the CMB predict the scale-invariant gravitational wave (GW) background of inflation to be out of reach for upcoming GW interferometers. This prospect dramatically changes if the inflaton is a pseudoscalar, in which case its generic coupling to any abelian gauge field provides a new source of GWs, directly related to the dynamics of inflation. This opens up new ways of probing the scalar potential responsible for cosmic inflation. Dividing inflation models into universality classes, we analyze the possible observational signatures. One of the most promising scenarios is Starobinsky inflation, which may lead to observational signatures both in direct GW detection as well as in upcoming CMB detectors. In this case, the complementarity between the CMB and direct GW detection, as well as the possibility of a multi-frequency analysis with upcoming ground and space based GW interferometers, may provide a first clue to the microphysics of inflation.

astro-ph.CO↗

arXiv2018

Unified Model of D-Term Inflation

Hybrid inflation, driven by a Fayet-Iliopoulos (FI) D term, is an intriguing inflationary model. In its usual formulation, it however suffers from several shortcomings. These pertain to the origin of the FI mass scale, the stability of scalar fields during inflation, gravitational corrections in supergravity, as well as to the latest constraints from the cosmic microwave background. We demonstrate that these issues can be remedied if D-term inflation is realized in the context of strongly coupled supersymmetric gauge theories. We suppose that the D term is generated in consequence of dynamical supersymmetry breaking. Moreover, we assume canonical kinetic terms in the Jordan frame as well as an approximate shift symmetry along the inflaton direction. This provides us with a unified picture of D-term inflation and high-scale supersymmetry breaking. The D term may be associated with a gauged U(1)_B-L, so that the end of inflation spontaneously breaks B-L in the visible sector.

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arXiv2018

Inflation from High-Scale Supersymmetry Breaking

Supersymmetry breaking close to the scale of grand unification can explain cosmic inflation. As we demonstrate in this paper, this can be achieved in strongly coupled supersymmetric gauge theories, such that the energy scales of inflation and supersymmetry breaking are generated dynamically. As a consequence, both scales are related to each other and exponentially suppressed compared to the Planck scale. As an example, we consider a dynamical model in which gauging a global flavor symmetry in the supersymmetry-breaking sector gives rise to a Fayet-Iliopoulos D term. This results in successful D-term hybrid inflation in agreement with all theoretical and phenomenological constraints. The gauged flavor symmetry can be identified with U(1)_B-L, where B and L denote baryon and lepton number, respectively. In the end, we arrive at a consistent cosmological scenario that provides a unified picture of high-scale supersymmetry breaking, viable D-term hybrid inflation, spontaneous B-L breaking at the scale of grand unification, baryogenesis via leptogenesis, and standard model neutrino masses due to the type-I seesaw mechanism.

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arXiv2018

Leptogenesis, dark matter and neutrino masses

We review the viability of the sterile neutrino hypothesis in accounting for three observational problems of the Standard Model of particle physics: neutrino masses and lepton mixing, dark matter and the baryon asymmetry of the Universe. We present two alternative scenarios for the implementation of the sterile fermion hypothesis: the $ν$MSM and the Inverse Seesaw.

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arXiv2018

Neutrino masses, leptogenesis and dark matter from small lepton number violation?

We consider the possibility of simultaneously addressing the baryon asymmetry of the Universe, the dark matter problem and the neutrino mass generation in minimal extensions of the Standard Model via sterile fermions with (small) total lepton number violation. Within the framework of Inverse and Linear Seesaw models, the small lepton number violating parameters set the mass scale of the active neutrinos, the efficiency of leptogenesis through a small mass splitting between pairs of sterile fermions as well as the mass scale of a sterile neutrino dark matter candidate. We provide an improved parametrization of these seesaw models taking into account existing experimental constraints and derive a linearized system of Boltzmann equations to describe the leptogenesis process, which allows for an efficient investigation of the parameter space. This in particular enables us to perform a systematic study of the strong washout regime of leptogenesis. Our study reveals that one can have a successful leptogenesis at the temperature of the electroweak scale through oscillations between two sterile states with a natural origin of the (necessary) strong degeneracy in their mass spectrum. The minimal model however requires a non-standard cosmological history to account for the relic dark matter. Finally, we discuss the prospect for neutrinoless double beta decay and for testing, in future experiments, the values of mass and different active-sterile mixings required for successful leptogenesis.

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arXiv2017

Lepton number violation as a key to low-scale leptogenesis

We explore the possibility of having a successful leptogenesis through oscillations between new sterile fermion states added to the Standard Model field content in a well motivated framework, naturally giving rise to the required mass splitting between the sterile states through a small total lepton number violation. We propose a framework with only two sterile states forming a pseudo-Dirac state, in which their mass difference as well as the smallness of the neutrino masses are due to two sources of lepton number violation with $ΔL=2$, corresponding to an Inverse Seesaw framework extended by a Linear Seesaw mass term. We also explore the pure Inverse Seesaw mechanism in its minimal version, requiring at least four new sterile states in order to comply with neutrino data. Our analytical and numerical studies reveal that one can have a successful leptogenesis at the temperature of the electroweak scale through oscillations between the two sterile states with a "natural" origin of the strong degeneracy in their mass spectrum. We also revisit the analytical expression of the baryon asymmetry of the Universe in the weak washout regime of this framework.

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arXiv2017

PBH dark matter from axion inflation

Protected by an approximate shift symmetry, axions are well motivated candidates for driving cosmic inflation. Their generic coupling to the Chern-Simons term of any gauge theory gives rise to a wide range of potentially observable signatures, including equilateral non-Gaussianites in the CMB, chiral gravitational waves in the range of direct gravitational wave detectors and primordial black holes (PBHs). In this paper we revisit these predictions for axion inflation models non-minimally coupled to gravity. Contrary to the case of minimally coupled models which typically predict scale-invariant mass distributions for the generated PBHs at small scales, we demonstrate how broadly peaked PBH spectra naturally arises in this setup. For specific parameter values, all of dark matter can be accounted for by PBHs.

astro-ph.CO↗

arXiv2017

Detection prospects for the Cosmic Neutrino Background using laser interferometers

The cosmic neutrino background is a key prediction of Big Bang cosmology which has not been observed yet. The movement of the earth through this neutrino bath creates a force on a pendulum, as if it was exposed to a cosmic wind. We revise here estimates for the resulting pendulum acceleration and compare it to the theoretical sensitivity of an experimental setup where the pendulum position is measured using current laser interferometer technology as employed in gravitational wave detectors. We discuss how a significant improvement of this setup can be envisaged in a micro gravity environment. The proposed setup could simultaneously function as a dark matter detector in the sub-MeV range, which currently eludes direct detection constraints.

astro-ph.CO↗

arXiv2017

Supergravity Contributions to Inflation in models with non-minimal coupling to gravity

This paper provides a systematic study of supergravity contributions relevant for inflationary model building in Jordan frame supergravity. In this framework, canonical kinetic terms in the Jordan frame result in the separation of the Jordan frame scalar potential into a tree-level term and a supergravity contribution, which is potentially dangerous for sustaining inflation. We show that if the vacuum energy necessary for driving inflation originates dominantly from the F-term of an auxiliary field (i.e. not the inflaton), the supergravity corrections to the Jordan frame scalar potential are generically suppressed. Moreover, these supergravity contributions identically vanish if the superpotential $W$ vanishes along the inflationary trajectory. On the other hand, if the F-term associated with the inflaton dominates the vacuum energy, the supergravity contributions are generically comparable to the globally supersymmetric contributions. In addition, the non-minimal coupling to gravity inherent to Jordan frame supergravity significantly impacts the inflationary model depending on the size and sign of this coupling. We discuss the phenomenology of some representative inflationary models, and point out the relation to the recently much discussed cosmological `attractor' models.

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arXiv2016

Science with the space-based interferometer LISA. IV: Probing inflation with gravitational waves

We investigate the potential for the LISA space-based interferometer to detect the stochastic gravitational wave background produced from different mechanisms during inflation. Focusing on well-motivated scenarios, we study the resulting contributions from particle production during inflation, inflationary spectator fields with varying speed of sound, effective field theories of inflation with specific patterns of symmetry breaking and models leading to the formation of primordial black holes. The projected sensitivities of LISA are used in a model-independent way for various detector designs and configurations. We demonstrate that LISA is able to probe these well-motivated inflationary scenarios beyond the irreducible vacuum tensor modes expected from any inflationary background.

astro-ph.CO↗

arXiv2016

Lepton number symmetry as a way to testable leptogenesis

We propose a minimal and motivated extension of the Standard Model characterised by an approximate lepton number conservation, which is able to simultaneously generate neutrino masses and to account for a successful baryogenesis via leptogenesis. The sterile fermions involved in the leptogenesis process have masses at the GeV scale. We determine the viable parameter space that complies with both the neutrino and baryogenesis phenomenology, and analyse the different regimes for the generation of a lepton asymmetry in the early Universe (weak and strong-washout) in order to determine their testability in future experimental facilities.

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arXiv2016

Probing inflation models with gravitational waves

A direct detection of primordial gravitational waves is the ultimate probe for any inflation model. While current CMB bounds predict the generic scale-invariant gravitational wave spectrum from slow-roll inflation to be below the reach of upcoming gravitational wave interferometers, this prospect may dramatically change if the inflaton is a pseudoscalar. In this case, a coupling to any abelian gauge field leads to a tachyonic instability for the latter and hence to a new source of gravitational waves, directly related to the dynamics of inflation. In this contribution we discuss how this setup enables the upcoming gravitational wave interferometers advanced LIGO/VIRGO and eLISA to probe the microphysics of inflation, distinguishing between different universality classes of single-field slow-roll inflation models. We find that the prime candidate for an early detection is a Starobinsky-like model.

astro-ph.CO↗

arXiv2016

Stable lepton mass matrices

We study natural lepton mass matrices, obtained assuming the stability of physical flavour observables with respect to the variations of individual matrix elements. We identify all four possible stable neutrino textures from algebraic conditions on their entries. Two of them turn out to be uniquely associated to specific neutrino mass patterns. We then concentrate on the semi-degenerate pattern, corresponding to an overall neutrino mass scale within the reach of future experiments. In this context we show that i) the neutrino and charged lepton mixings and mass matrices are largely constrained by the requirement of stability, ii) naturalness considerations give a mild preference for the Majorana phase most relevant for neutrinoless double-beta decay, $α\sim π/2$, and iii) SU(5) unification allows to extend the implications of stability to the down quark sector. The above considerations would benefit from an experimental determination of the PMNS ratio $|U_{32}/U_{31}|$, i.e. of the Dirac phase $δ$.

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arXiv2015

Constraints on the reheating temperature from sizable tensor modes

Despite its importance for modeling the homogeneous hot early universe very little is experimentally known about the magnitude of the reheating temperature, leaving an uncertainty of remarkable 18 orders of magnitude. In this paper we consider a general class of polynomial inflaton potentials up to fourth order. Employing a Monte Carlo scan and imposing theoretical and experimental constraints we derive a robust lower limit on the energy scale at the end of inflation, $V_\text{end}^{1/4} > 3 \times 10^{15}$ GeV for sizable tensor modes, $r \geq 10^{-3}$. If the reheating phase is perturbative and matter dominated, this translates into a lower bound on the reheating temperature, yielding $T_\text{rh} > 3 \times 10^8 \; (7 \times 10^2)$ GeV for gravitational inflaton decay through a generic dimension five (six) operator.

astro-ph.CO↗

arXiv2015

A Minimal Supersymmetric Model of Particle Physics and the Early Universe

We consider a minimal supersymmetric extension of the Standard Model, with right-handed neutrinos and local B-L, the difference between baryon and lepton number, a symmetry which is spontaneously broken at the scale of grand unification. To a large extent, the parameters of the model are determined by gauge and Yukawa couplings of quarks and leptons. We show that this minimal model can successfully account for the earliest phases of the cosmological evolution: Inflation is driven by the energy density of a false vacuum of unbroken B-L symmetry, which ends in tachyonic preheating, i.e. the decay of the false vacuum, followed by a matter dominated phase with heavy B-L Higgs bosons. Nonthermal and thermal processes produce an abundance of heavy neutrinos whose decays generate primordial entropy, baryon asymmetry via leptogenesis and dark matter consisting of gravitinos or nonthermal WIMPs. The model predicts relations between neutrino and superparticle masses and a characteristic spectrum of gravitational waves.

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arXiv2014

Dwarf spheroidal galaxies as degenerate gas of free fermions

In this paper we analyze a simple scenario in which Dark Matter (DM) consists of free fermions with mass $m_f$. We assume that on galactic scales these fermions are capable of forming a degenerate Fermi gas, in which stability against gravitational collapse is ensured by the Pauli exclusion principle. The mass density of the resulting configuration is governed by a non-relativistic Lane-Emden equation, thus leading to a universal cored profile that depends only on one free parameter in addition to $m_f$. After reviewing the basic formalism, we test this scenario against experimental data describing the velocity dispersion of the eight classical dwarf spheroidal galaxies of the Milky Way. We find that, despite its extreme simplicity, the model exhibits a good fit to the data and realistic predictions for the size of DM halos providing that $m_f\simeq 200$ eV. Furthermore, we show that in this setup larger galaxies correspond to the non-degenerate limit of the gas. We propose a concrete realization of this model in which DM is produced non-thermally via inflaton decay. We show that imposing the correct relic abundance and the bound on the free-streaming length constrains the inflation model in terms of inflaton mass, its branching ratio into DM and the reheating temperature.

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