arXiv subjects

Mansoor Ur Rehman

Publications and source records attributed to Mansoor Ur Rehman.

48 records · Page 3Linked to original sources

arXiv2011

Non-Minimal B-L Inflation with Observable Gravity Waves

We consider non-minimal λϕ^4 inflation in a gauged non-supersymmetric U(1)_{B-L} model containing the gravitational coupling ξ\mathcal{R} Φ^\dagger Φ, where \mathcal{R} denotes the Ricci scalar and the standard model singlet inflaton field Φspontaneously breaks the U(1)_{B-L} symmetry. Including radiative corrections, the predictions 0.956 < n_s < 0.984 and 0.007 < r < 0.1 for the scalar spectral index and tensor to scalar ratio r lie within the current WMAP 1-σbounds. If the B-L symmetry breaking scale is of order a TeV or so, one of the three right handed neutrinos is a plausible cold dark matter candidate. Bounds on the dimensionless parameters λ, ξand the gauge coupling g_{B-L} are obtained.

hep-ph↗

arXiv2011

Red Spectral Tilt and Observable Gravity Waves in Shifted Hybrid Inflation

We consider supersymmetric shifted hybrid inflation models with a red tilted scalar spectral index n_s in agreement with the WMAP 7-yr central value. If non-minimal supergravity corrections are included, these models can also support a tensor-to-scalar ratio as large as r = 0.02, which may be observable by the Planck Satellite. In contrast to the standard supersymmetric hybrid inflation scenario, topological defects produced via gauge symmetry breaking are inflated away in the shifted version of the theory.

astro-ph.CO↗

arXiv2010

Observable Gravity Waves from Supersymmetric Hybrid Inflation II

It is shown that a tensor-to-scalar ratio close to r = 0.03, which can be observed by Planck, is realized in supersymmetric hybrid inflation models with TeV-scale soft supersymmetry breaking terms. This extends our previous analysis, which also found r <~ 0.03 but employed intermediate scale soft terms. Other cosmological observables such as the scalar spectral index are in good agreement with the WMAP data.

astro-ph.CO↗

arXiv2010

Tensor to Scalar Ratio in Non-Minimal $ϕ^4$ Inflation

We reconsider non-minimal λϕ^4 chaotic inflation which includes the gravitational coupling term ξ\mathcal{R} ϕ^2, where ϕdenotes a gauge singlet inflaton field and \mathcal{R} is the Ricci scalar. For ξ>> 1 we require, following recent discussions, that the energy scale λ^{1/4} m_P / \sqrtξ for inflation should not exceed the effective UV cut-off scale m_P / ξ, where m_P denotes the reduced Planck scale. The predictions for the tensor to scalar ratio r and the scalar spectral index n_s are found to lie within the WMAP 1-σbounds for 10^{-12} < λ< 10^{-4} and 10^{-3} < ξ< 10^2. In contrast, the corresponding predictions of minimal λϕ^4 chaotic inflation lie outside the WMAP 2-σbounds. We also find that r > 0.002, provided the scalar spectral index n_s > 0.96. In estimating the lower bound on r we take into account possible modifications due to quantum corrections of the tree level inflationary potential.

hep-ph↗

arXiv2010

Higgs Inflation, Quantum Smearing and the Tensor to Scalar Ratio

In cosmic inflation driven by a scalar gauge singlet field with a tree level Higgs potential, the scalar to tensor ratio r is estimated to be larger than 0.036, provided the scalar spectral index n_s >= 0.96. We discuss quantum smearing of these predictions arising from the inflaton couplings to other particles such as GUT scalars, and show that these corrections can significantly decrease r. However, for n_s >= 0.96, we obtain r >= 0.02 which can be tested by the Planck satellite.

astro-ph.CO↗

arXiv2010

Supersymmetric Hybrid Inflation Redux

We discuss the important role played during inflation by one of the soft supersymmetry breaking terms in the inflationary potential of supersymmetric hybrid inflation models. With minimal Kaehler potential, the inclusion of this term allows the prediction for the scalar spectral index to agree with the value n_s = 0.963^{+0.014}_{-0.015} found by WMAP5. In the absence of this soft term, and by taking into account only radiative and supergravity corrections, it is well known that n_s >= 0.985. This same soft term has previously been shown to play a key role in resolving the MSSM mu problem. The tensor to scalar ratio r is quite small in these models, taking on values r <= 10^{-5} in the WMAP5 2-sigma range of n_s.

hep-ph↗

arXiv2009

Minimal Supersymmetric Hybrid Inflation, Flipped SU(5) and Proton Decay

Minimal supersymmetric hybrid inflation utilizes a canonical Kahler potential and a renormalizable superpotential which is uniquely determined by imposing a U(1) R-symmetry. In computing the scalar spectral index $n_s$ we take into account modifications of the tree level potential caused by radiative and supergravity corrections, as well as contributions from the soft supersymmetry breaking terms with a negative soft mass-squared term allowed for the inflaton. All of these contributions play a role in realizing $n_s$ values in the range 0.96-0.97 preferred by WMAP. The U(1) R-symmetry plays an important role in flipped SU(5) by eliminating the troublesome dimension five proton decay. The proton decays into $e^+ π^0$ via dimension six operators arising from the exchange of superheavy gauge bosons with a lifetime of order $10^{34}$-$10^{36}$ years.

hep-ph↗

arXiv2009

Running Standard Model Inflation And Type I Seesaw

Several authors have recently argued that a satisfactory inflationary scenario can be implemented in the Standard Model (SM) by introducing a strong non-minimal coupling of the Higgs doublet to gravity. It is shown here that type I seesaw physics containing right handed neutrinos at intermediate scales can have a significant impact on the inflationary predictions of these models. For one such model, values of the scalar spectral index lower than the tree level prediction of 0.968 are realized for plausible values of the seesaw parameters and a SM Higgs boson mass close to 130 GeV. A precise measurement of n_s by PLANCK, as well as measurement of the Higgs boson mass by LHC should provide stringent tests of this SM based inflationary scenario supplemented by type I seesaw physics.

hep-ph↗

arXiv2009

Amelioration of Little Hierarchy Problem in SU(4)_c x SU(2)_L x SU(2)_R

The little hierarchy problem encountered in the constrained minimal supersymmetric model (CMSSM) can be ameliorated in supersymmetric models based on the gauge symmetry G_{422} \equiv SU(4)_c x SU(2)_L x SU(2)_R. The standard assumption in CMSSM (and in SU(5) and SO(10)) of universal gaugino masses can be relaxed in G_{422}, and this leads to a significant improvement in the degree of fine tuning required to implement radiative electroweak breaking in the presence of a characteristic supersymmetry breaking scale of around a TeV. Examples of Higgs and sparticle mass spectra realized with 10% fine tuning are presented.

hep-ph↗

arXiv2009

Hybrid Inflation Revisited in Light of WMAP5

We study the effects of including one-loop radiative corrections in a non-supersymmetric hybrid inflationary model. These corrections can arise from Yukawa couplings between the inflaton and right-handed neutrinos, and induce a maximum in the potential which admits hilltop-type solutions in addition to the standard hybrid solutions. We obtain a red-tilted spectral index $n_s$, consistent with WMAP5 data, for sub-Planckian values of the field. This is in contrast to the tree level hybrid analysis, in which a red-tilted spectrum is achieved only for trans-Planckian values of the field. Successful reheating is obtained at the end of the inflationary phase via conversion of the inflaton and waterfall fields into right-handed neutrinos, whose subsequent decay can explain the observed baryon asymmetry via leptogenesis.

hep-ph↗

arXiv2008

GUT Inflation and Proton Decay after WMAP5

We employ Coleman-Weinberg and Higgs potentials to implement inflation in non-supersymmetric grand unified theories (GUTs) such as SU(5) and SO(10). To realize a scalar spectral index close to 0.96, as indicated by the most recent WMAP 5-year anlaysis, the energy scale of observable inflation turns out to be of order $10^{16}$ GeV. This implies a GUT symmetry breaking scale of similar magnitude, and proton lifetime of order $10^{34}$-$10^{38}$ years. In some SO(10) models with axion dark matter, the scalar leptoquark boson exchange leads to proton decay with a lifetime of order $10^{34}$-$10^{35}$ years.

hep-ph↗

arXiv2008

Higgs Boson Mass, Sparticle Spectrum and Little Hierarchy Problem in Extended MSSM

We investigate the impact of TeV-scale matter belonging to complete vectorlike multiplets of unified groups on the lightest Higgs boson in the MSSM. We find that consistent with perturbative unification and electroweak precision data the mass m_h can be as large as 160 GeV. These extended MSSM models can also render the little hierarchy problem less severe, but only for lower values of m_h < 125 GeV. We present estimates for the sparticle mass spectrum in these models.

hep-ph↗