arXiv subjects

Kenji Kadota

Publications and source records attributed to Kenji Kadota.

71 records · Page 4Linked to original sources

arXiv2009

A Sneutrino NLSP in the $ν$CMSSM

We extend the constrained minimal supersymmetric model (CMSSM) by adding a right-handed neutrino superfield ($ν$CMSSM) which decouples close to the GUT scale. We study the effects of a right-handed neutrino on the low energy spectrum and focus on the predictions for dark matter properties. We pay particular attention to the realization of the light (left-handed) sneutrino which can be the next-to-lightest supersymmetric particle (NLSP) with either the neutralino or gravitino as the lightest supersymmetric particle (LSP). Notably, for the case of a neutralino LSP with a sneutrino NLSP, there are new `sneutrino coannihilation regions' which yield the desired thermal neutralino relic density determined by WMAP.

hep-ph↗

arXiv2009

CMBPol Mission Concept Study: Probing Inflation with CMB Polarization

We summarize the utility of precise cosmic microwave background (CMB) polarization measurements as probes of the physics of inflation. We focus on the prospects for using CMB measurements to differentiate various inflationary mechanisms. In particular, a detection of primordial B-mode polarization would demonstrate that inflation occurred at a very high energy scale, and that the inflaton traversed a super-Planckian distance in field space. We explain how such a detection or constraint would illuminate aspects of physics at the Planck scale. Moreover, CMB measurements can constrain the scale-dependence and non-Gaussianity of the primordial fluctuations and limit the possibility of a significant isocurvature contribution. Each such limit provides crucial information on the underlying inflationary dynamics. Finally, we quantify these considerations by presenting forecasts for the sensitivities of a future satellite experiment to the inflationary parameters.

astro-ph↗

arXiv2008

New D-term chaotic inflation in supergravity and leptogenesis

We present a new model of D-term dominated chaotic inflation in supergravity. The F-flat direction present in this model is lifted by the dominant D-term, which leads to chaotic inflation and subsequent reheating. No cosmic string is formed after inflation because the U(1) gauge symmetry is broken during inflation. The leptogenesis scenario via the inflaton decay in our D-term chaotic inflation scenario is also discussed.

hep-ph↗

arXiv2008

Sterile neutrino dark matter in warped extra dimensions

We consider a (long-lived) sterile neutrino dark matter scenario in a five dimensional (5D) warped extra dimension model where the fields can live in the bulk, which is partly motivated from the absence of the absolutely stable particles in a simple Randall-Sundrum model. The dominant production of the sterile neutrino can come from the decay of the radion (the scalar field representing the brane separation) around the electroweak scale. The suppressions of the 4D parameters due to the warp factor and the small wave function overlaps in the extra dimension help alleviate the exceeding fine-tunings typical for a sterile neutrino dark matter scenario in a 4D setup.

hep-ph↗

arXiv2007

D-term chaotic inflation in supergravity

Even though the chaotic inflation is one of the most popular inflation models for its simple dynamics and compelling resolutions to the initial condition problems, its realization in supergravity has been considered a challenging task. We discuss how the chaotic inflation dominated by the D-term can be induced in supergravity, which would give a new perspective on the inflation model building in supergravity.

hep-ph↗

arXiv2007

Warped Leptogenesis with Dirac Neutrino Masses

We show how leptogenesis can occur at the TeV scale with neutrinos that possess almost purely Dirac masses and negligible Majorana mass contributions as a consequence of the small wavefunction overlap in a warped fifth dimension. Lepton number violation at the Planck scale is introduced via a Majorana mass term on the Planck brane. Such a Majorana mass operator leads to the small mass splitting of otherwise degenerate Kaluza-Klein excited states on the TeV brane. This tiny mass splitting can compensate for the small Yukawa couplings to give a CP asymmetry large enough to produce the sufficient baryon asymmetry from the decay of the nearly degenerate neutrino Kaluza-Klein states. In this way the standard baryogenesis via leptogenesis scenario can naturally occur at the TeV scale without the need for a high mass scale.

hep-ph↗

arXiv2007

The Decay of the Inflaton in No-scale Supergravity

We study the decay of the inflaton in no-scale supergravity and show that decay due to the gravitational interactions through supergravity effects is highly suppressed relative to the case in minimal supergravity or models with a generic Kahler potential. We also show that decay to gravitinos is suppressed. We demonstrate that decay and sufficient reheating are possible with the introduction of a non-trivial gauge kinetic term. This channel may be dominant in no-scale supergravity, yet yields a re-heating temperature which is low enough to avoid the gravitino problem while high enough for Big Bang Nucleosynthesis and baryogenesis.

hep-ph↗

arXiv2006

Primordial non-Gaussianity and Dark Energy constraints from Cluster Surveys

Galaxy cluster surveys will be a powerful probe of dark energy. At the same time, cluster abundance is sensitive to any non-Gaussianity of the primordial density field. It is therefore possible that non-Gaussian initial conditions might be misinterpreted as a sign of dark energy or at least degrade the expected constraints on dark energy parameters. To address this issue, we perform a likelihood analysis of an ideal cluster survey similar in size and depth to the upcoming South Pole Telescope/Dark Energy Survey (SPT-DES). We analyze a model in which the strength of the non-Gaussianity is parameterized by the constant fNL; this model has been used extensively to derive Cosmic Microwave Background (CMB) anisotropy constraints on non-Gaussianity, allowing us to make contact with those works. We find that the constraining power of the cluster survey on dark energy observables is not significantly diminished by non-Gaussianity provided that cluster redshift information is included in the analysis. We also find that even an ideal cluster survey is unlikely to improve significantly current and future CMB constraints on non-Gaussianity. However, when all systematics are under control, it could constitute a valuable cross check to CMB observations.

astro-ph↗

arXiv2006

D-term Inflation and Leptogenesis by Right-handed Sneutrino

We discuss a D-term inflation scenario where a right-handed sneutrino can be an inflaton field leading to a viable inflation and leptogenesis, with a minimal form of Kähler potential. The decay of an inflaton sneutrino can non-thermally create large enough lepton asymmetry. Its entropy production is also big enough to ameliorate the gravitino problem caused by too high a reheating temperature from the decay of a symmetry breaking field.

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arXiv2005

Uncertainties in the S-Z selected cluster angular power spectrum

Large SZ selected galaxy cluster surveys are beginning imminently. We compare the dependence of the galaxy cluster angular power spectrum on cosmological parameters, different modeling assumptions and statistical observational errors. We quantify the degeneracies between theoretical assumptions such as the mass function and cosmological parameters such as $σ_8$. We also identify a rough scaling behavior of this angular power spectrum with $σ_8$ alone.

astro-ph↗

arXiv2005

Parameterizing the Power Spectrum: Beyond the Truncated Taylor Expansion

The power spectrum is traditionally parameterized by a truncated Taylor series: $ln P(k) = ln P_* + (n_*-1) ln(k/k_*) + {1/2} n'_* ln^2(k/k_*)$. It is reasonable to truncate the Taylor series if $|n'_* ln(k/k_*)| << |n_*-1|$, but it is not if $|n'_* ln(k/k_*)| \gtrsim |n_*-1|$. We argue that there is no good theoretical reason to prefer $|n'_*| << |n_*-1|$, and show that current observations are consistent with $|n'_* ln(k/k_*)| ~ |n_*-1|$ even for $|ln(k/k_*)| ~ 1$. Thus, there are regions of parameter space, which are both theoretically and observationally relevant, for which the traditional truncated Taylor series parameterization is inconsistent, and hence it can lead to incorrect parameter estimations. Motivated by this, we propose a simple extension of the traditional parameterization, which uses no extra parameters, but that, unlike the traditional approach, covers well motivated inflationary spectra with $|n'_*| ~ |n_*-1|$. Our parameterization therefore covers not only standard-slow-roll inflation models but also a much wider class of inflation models. We use this parameterization to perform a likelihood analysis for the cosmological parameters.

astro-ph↗

arXiv2005

Precision of Inflaton Potential Reconstruction from CMB Using the General Slow-Roll Approximation

Through a principal component analysis, we study how accurately CMB observables can constrain inflaton potentials in a model independent manner. We apply the general slow-roll approximation in our analysis where we allow, in contrast to the standard slow-roll approximation, the possibility of variations in $V''(ϕ)$ and take into account the fact that horizon crossing is not an instantaneous event. Our analysis provides a set of modes to be used in fitting observables. We find that of order five of these modes will be constrained by future observations, so a fully general data analysis package could use the amplitudes of just a handful of modes as free parameters and retain all relevant information in the data.

astro-ph↗

arXiv2004

Inflation model building in moduli space

A self-consistent modular cosmology scenario and its testability in view of future CMB experiments are discussed. Particular attention is drawn to the enhanced symmetric points in moduli space which play crucial roles in our scenario. The running and moreover the running of running for the cosmic perturbation spectrum are also analyzed.

hep-ph↗

arXiv2004

Modular Cosmology, Thermal Inflation, Baryogenesis and Predictions for Particle Accelerators

Modular cosmology is plagued by overproduction of unwanted relics, gravitinos and especially moduli, at relatively low energy scales. Thermal inflation provides a compelling solution to this moduli problem, but invalidates most baryogenesis scenarios. We propose a simple model in which the MSSM plus neutrino mass term $(LH_u)^2$ is supplemented by a minimal flaton sector to drive the thermal inflation, and make two crucial assumptions: the flaton vacuum expectation value generates the $μ$-term of the MSSM and $m_L^2 + m_{H_u}^2 < 0$. The second assumption is particularly interesting in that it violates a well known constraint, implying that there exists a nearby deep non-MSSM vacuum, and provides a clear signature of our model which can be tested at future particle accelerators. We show that our model leads to thermal inflation followed by Affleck-Dine leptogenensis along the $LH_u$ flat direction. A key feature of our leptogenesis scenario is that the $H_uH_d$ flat direction is also induced to temporarily acquire a large value, playing a crucial role in the leptogenesis, as well as dynamically shielding the field configuration from the deep non-MSSM minimum, ensuring that the fields relax into our MSSM vacuum.

hep-ph↗

arXiv2003

Inflation on Moduli Space and Cosmic Perturbations

We show that a moduli space of the form predicted by string theory, lifted by supersymmetry breaking, gives rise to successful inflation for large regions of parameter space without any modification or fine tuning. This natural realization of inflation relies crucially on the complex nature of the moduli fields and the multiple points of enhanced symmetry, which are generic features of moduli space but not usually considered in inflationary model building. Our scenario predicts cosmic perturbations with an almost exactly flat spectrum for a wide range of scales with running on smaller, possibly observable, scales. The running takes the form of either an increasingly steep drop off of the spectrum, or a rise to a bump in the spectrum before an increasingly steep drop off.

hep-ph↗

arXiv2003

Successful Modular Cosmology

We present a modular cosmology scenario where the difficulties encountered in conventional modular cosmology are solved in a self-consistent manner, with definite predictions to be tested by observation. Notably, the difficulty of the dilaton finding its way to a precarious weak coupling minimum is made irrelevant by having eternal modular inflation at the vacuum supersymmetry breaking scale after the dilaton is stabilised. Neither this eternal inflation nor the subsequent non-slow-roll modular inflation destabilise the dilaton from its precarious minimum due to the low energy scale of the inflation and consequent small back reaction on the dilaton potential. The observed flat CMB spectrum is obtained from fluctuations in the angular component of a modulus near a symmetric point, which are hugely magnified by the roll down of the modulus to Planckian values, allowing them to dominate the final curvature perturbation. We also give precise calculations of the spectral index and its running.

hep-ph↗

arXiv2003

Supergravity Inflation Free from Harmful Relics

We present a realistic supergravity inflation model which is free from the overproduction of potentially dangerous relics in cosmology, namely moduli and gravitinos which can lead to the inconsistencies with the predictions of baryon asymmetry and nucleosynthesis. The radiative correction turns out to play a crucial role in our analysis which raises the mass of supersymmetry breaking field to intermediate scale. We pay a particular attention to the non-thermal production of gravitinos using the non-minimal Kahler potential we obtained from loop correction. This non-thermal gravitino production however is diminished because of the relatively small scale of inflaton mass and small amplitudes of hidden sector fields.

hep-ph↗