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Leszek Roszkowski

Publications and source records attributed to Leszek Roszkowski.

105 records · Page 6Linked to original sources
arXiv1998

Observational constraints on an inflation model with a running mass

We explore a model of inflation where the inflaton mass-squared is generated at a high scale by gravity-mediated soft supersymmetry breaking, and runs at lower scales to the small value required for slow-roll inflation. The running is supposed to come from the coupling of the inflaton to a non-Abelian gauge field. In contrast with earlier work, we do not constrain the magnitude of the supersymmetry breaking scale, and we find that the model might work even if squark and slepton masses come from gauge-mediated supersymmetry breaking. With the inflaton and gaugino masses in the expected range, and $α= g^2/4π$ in the range $10^{-2}$ to $10^{-3}$ (all at the high scale) the model can give the observed cosmic microwave anisotropy, and a spectral index in the observed range. The latter has significant variation with scale, which can confirm or rule out the model in the forseeable future.

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arXiv1998

The Supersymmetric Flavour and CP Problems From a Cosmological Perspective

The supersymmetric flavour and CP problems can be avoided if the first two generations of sfermions are heavier than a few TeV and approximately degenerate in mass. However using flavour and CP-violating constraints on the third sfermion generation, together with the decoupling of the first two generations, can dramatically affect cosmological predictions such as the relic abundance of stable particles. In particular, we show that if the lightest supersymmetric particle is essentially bino-like then requiring that all flavour changing neutral current and CP-violating processes are adequately suppressed, imposes severe limits on the bino mass, where typically m_bino>(200-300) GeV. This leads to difficulties for models implementing the scenario of heavy sfermion masses.

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arXiv1996

Constraints from Inflation and Reheating on Superpartner Masses

Flat directions in the Minimal Supersymmetric Standard Model (MSSM) can become unstable due to radiative corrections, and the global minimum of the (zero temperature) potential can lie at large values of the squark and/or slepton fields. Here we show that, in inflationary models of early cosmology, the universe is very likely to be in the domain of attraction of this global minimum at the end of inflation. While the minimum at the origin of field space is global at sufficiently high temperatures, depending on details of the model, the universe may be trapped in the non-zero minimum until it becomes the global minimum at low temperatures. Parameter values leading to this scenario are therefore ruled out.

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arXiv1995

New Constraints on Superpartner Masses

We consider the Minimal Supersymmetric Standard Model (MSSM) without imposing relations on the superpartner masses that arise in grand unified theories. Given an arbitrary pattern of superpartner masses (consistent with experimental constraints), it may happen that the scalar potential is actually unstable, even though all scalar masses-squared are positive at the weak scale $M_W$. This is most likely to happen if the running mass-squared in a ``flat'' direction in field space becomes negative at some scale $Q_0$ which is well below the GUT scale. In this case, either this pattern of masses is ruled out, or there must be new physics (beyond the MSSM) at or below the scale $Q_0$.

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arXiv1994

Dark Matter from Supersymmetric Grand Unification

In constrained minimal supersymmetry the lightest neutralino of bino-type is the only neutral candidate for dark matter. As a result, one is typically able to restrict all the supersymmetric mass spectra below roughly 1-2\tev\ {\em without} imposing an ill-defined fine-tuning constraint.

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arXiv1994

Upper Bounds in Low-Energy SUSY

In the constrained MSSM one is typically able to restrict the supersymmetric mass spectra below roughly 1-2\tev\ {\em without} resorting to the ambiguous fine-tuning constraint.

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arXiv1994

Predictions for Constrained Minimal Supersymmetry with Bottom-Tau Mass Unification

We examine the Constrained Minimal Supersymmetric Standard Model (CMSSM) with an additional requirement of strict b - tau unification in the region of small tan(beta). We find that the parameter space becomes completely limited below about 1 TeV by physical constraints alone, without a fine-tuning constraint. We study the resulting phenomenological consequences, and point out several ways of falsifying the adopted b - tau unification assumption. We also comment on the effect of a constraint from the non-observation of proton decay.

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arXiv1993

Study of Constrained Minimal Supersymmetry

Taking seriously phenomenological indications for supersymmetry, we have made a detailed study of unified minimal SUSY, including effects at the few percent level in a consistent fashion. We report here a general analysis without choosing a particular unification gauge group. We find that the encouraging SUSY unification results of recent years do survive the challenge of a more complete and accurate analysis. Taking into account effects at the 5-10% level leads to several improvements of previous results, and allows us to sharpen our predictions for SUSY in the light of unification. We perform a thorough study of the parameter space. The results form a well-defined basis for comparing the physics potential of different facilities. Very little of the acceptable parameter space has been excluded by LEP or FNAL so far, but a significant fraction can be covered when these accelerators are upgraded. A number of initial applications to the understanding of the SUSY spectrum, detectability of SUSY at LEP II or FNAL, BR($b\to sγ$), Width($Z\to b\bar b$), dark matter, etc, are included in a separate section. We formulate an approach to extracting SUSY parameters from data when superpartners are detected. For small tan(beta) or large $m_top$ both $M_half$ and $M_0$ are entirely bounded from above at O(1 tev) without having to use a fine-tuning constraint.

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arXiv1993

SUSY-GUT Higgs Probe at Future $e^+e^-$ Colliders

Several independent constraints on the minimal supersymmetric model with constraints from grand unifications and cosmology select the region of low-energy supersymmetry below ${\cal O}$(1~TeV). The resulting mass of the lightest Higgs boson can probably be covered at LEP II only if its beam energy exceeds 200~GeV, and is within the detectability range of the NLC with $\sqrt{s}=300$~GeV.

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arXiv1993

Supersymmetric Dark Matter - a Review

I address the question of whether supersymmetry provides a viable candidate for the dark matter in the Universe. I review the properties of the lightest neutralino as a candidate for solving the dark matter problem. I discuss the neutralino's phenomenological and cosmological properties, and constraints from present and future experiments. In the minimal supersymmetric model, the neutralino mass has been experimentally excluded below some $20$ GeV, and is not expected to be significantly larger than about $150$ GeV. I identify a gaugino-like neutralino as the most natural dark matter candidate for a plausible range of parameters. The requirement that the lightest neutralino be the dominant matter component in the flat Universe provides non-trivial restrictions on other parameters of the model, in particular on the masses of the sfermions. Next, I study the consequences of adopting further grand unification assumptions. In both scenarios I find sfermion masses most likely beyond the reach of LEP 200 and the Tevatron but well within the discovery potential of the SSC and the LHC. I also comment on the effects of relaxing grand unification assumptions. Finally, I briefly outline prospects for the neutralino dark matter searches.

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arXiv1992

On the COBE Discovery - for Pedestrians

A recent discovery by the COBE satellite is presented, and its importance discussed in the context of the physics of the early Universe. The various implications for our understanding of the structure of the Universe are outlined.

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