arXiv subjects

Qaisar Shafi

Publications and source records attributed to Qaisar Shafi.

At least 163 records · Page 9Linked to original sources

arXiv2010

WIMP Dark Matter Inflation with Observable Gravity Waves

We present a successful inflation model based on $λϕ^4$ potential in which a Standard Model (SM) singlet inflaton $ϕ$, with mass of around a TeV or less, also plays the role of a weakly interacting scalar dark matter particle (WIMP). The WIMP relic abundance generated after inflation is in accord with the current observations. The spectral index $n_s$ lies within the WMAP 1-$σ$ bounds, while the Planck satellite may observe the tensor-to-scalar ratio, a canonical measure of gravity waves, which we estimate lies between 0.003 and 0.007.An unbroken $Z_2$ parity ensures that the scalar WIMP is absolutely stable.

hep-ph↗

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

New Fermions at the LHC and Mass of the Higgs Boson

Unification at M_{GUT}\sim 3\times 10^{16} GeV of the three Standard Model (SM) gauge couplings can be achieved by postulating the existence of a pair of vectorlike fermions carrying SM charges and masses of order 300 GeV -- 1 TeV. The presence of these fermions significantly modifies the vacuum stability and perturbativity bounds on the mass of the SM Higgs boson. The new vacuum stability bound in this extended SM is estimated to be 117 GeV, to be compared with the SM prediction of about 128 GeV. An upper bound of 190 GeV is obtained based on perturbativity arguments. The impact on these predictions of type I seesaw physics is also discussed. The discovery of a relatively `light' Higgs boson with mass \sim 117 GeV could signal the presence of new vectorlike fermions within reach of the LHC.

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

Color Triplet Diquarks at the LHC

We consider a class of supersymmetric models containing baryon number violating processes such as observable neutron - antineutron oscillations that are mediated by color triplet diquark fields. For plausible values of the diquark-quark couplings, the scalar diquark with mass between a few hundred GeV and one TeV or so can be produced in the s-channel at the LHC and detected through its decay into a top quark and a hadronic jet.

hep-ph↗

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

CDMS II Inspired Neutralino Dark Matter in Flipped SU(5)

We investigate neutralino dark matter in supersymmetric flipped SU(5), focusing on candidates with masses of order 30 - 150 GeV and spin independent cross sections that are consistent with the most recent CDMS II results. We assume gravity mediated supersymmetry breaking and restrict the magnitude of the soft supersymmetry breaking mass parameters to 1 TeV or less. With non-universal soft gaugino and Higgs masses, and taking flipped SU(5) into account, we identify allowed regions of the parameter space and highlight some benchmark solutions including Higgs and sparticle spectroscopy.

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

Coannihilation Scenarios and Particle Spectroscopy in SU(4)_c x SU(2)_L x SU(2)_R

We identify a variety of coannihilation scenarios in a supersymmetric SU(4)_c x SU(2)_L x SU(2)_R model with discrete left-right symmetry. Non-universal gaugino masses, compatible with the gauge symmetry, play an essential role in realizing gluino and bino-wino coannihilation regions that are consistent with the WMAP dark matter constraints. We also explore regions of the parameter space in which the little hierarchy problem is partially resolved. We present several phenomenologically interesting benchmark points and the associated sparticle and Higgs mass spectra.

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

Type II Seesaw and the PAMELA/ATIC Signals

We discuss how the cosmic ray signals reported by the PAMELA and ATIC/PPB-BETS experiments may be understood in a Standard Model (SM) framework supplemented by type II seesaw and a stable SM singlet scalar boson as dark matter. A particle physics explanation of the 'boost' factor can be provided by including an additional SM singlet scalar field.

hep-ph↗

arXiv2009

Yukawa Unification and Neutralino Dark Matter in SU(4)_c \times SU(2)_L \times SU(2)_R

We consider a left-right symmetric SU(4)_c \times SU(2)_L \times SU(2)_R (4-2-2) model with gravity mediated supersymmetry breaking. We find that with 4-2-2 compatible non-universal gaugino masses, t-b-τYukawa coupling unification is consistent with neutralino dark matter abundance and with constraints from collider experiments (except (g-2)_μ). The gluino mass lies close to that of the lightest neutralino, so that the gluino co-annihilation channel plays an important role in determining the neutralino relic abundance. By relaxing the Yukawa unification constraint we find stau and stop masses as low as 200-220 GeV. We highlight some benchmark points for these cases with 40 < \tanβ< 58.

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↗

arXiv2009

CMSSM Spectroscopy in light of PAMELA and ATIC

Dark matter neutralinos in the constrained minimal supersymmetric model (CMSSM) may account for the recent cosmic ray electron and positron observations reported by the PAMELA and ATIC experiments either through self annihilation or via decay. However, to achieve this, both scenarios require new physics beyond the 'standard' CMSSM, and a unified explanation of the two experiments suggests a neutralino mass of order 700 GeV - 2 TeV. A relatively light neutralino with mass around 100 GeV (300 GeV) can accomodate the PAMELA but not the ATIC observations based on a model of annihilating (decaying) neutralinos. We study the implications of these scenarios for Higgs and sparticle spectroscopy in the CMSSM and highlight some benchmark points. An estimate of neutrino flux expected from the annihilating and decaying neutralino scenarios is provided.

hep-ph↗

arXiv2008

Soft Probes of SU(5) Unification

We explore the sparticle and Higgs spectroscopy of an SU(5) inspired extension of the constrained minimal supersymmetric standard model (CMSSM). The universal soft parameter m_0 is replaced by m_{\bar 5} and m_{10}, where m_{\bar 5} and m_{10} denote universal soft scalar masses associated with fields in the five and ten dimensional representations of SU(5). The special case m_{\bar 5} << m_{10} yields a rather characteristic sparticle spectroscopy which can be tested at the LHC. We highlight a few benchmark points in which the lightest neutralino saturates the WMAP bound on cold dark matter abundance.

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

NMSSM and Seesaw Physics at LHC

We consider extensions of the next-to-minimal supersymmetric model (NMSSM) in which the observed neutrino masses are described in terms of effective dimension six (or seven) rather than dimension five operators. All such operators respect the discrete symmetries of the model. The new particles associated with the double (or triple) seesaw mechanism can have sizable couplings to the known leptons, even with a TeV seesaw scale. In the latter case some of these new short-lived particles could be produced and detected at the LHC.

hep-ph↗