Back-door fine-tuning in supersymmetric low scale inflation

Low scale inflation has many virtues and it has been claimed that its natural realisation in supersymmetric standard model can be achieved rather easily. In this letter we have demonstrated that also in this case the dynamics of the hidden sector responsible for supersymmetry breakdown and the structure of the soft terms affects significantly, and in fact often spoils, the would-be inflationary dynamics. Also, we point out that the issue if the cosmological constant cancellation in the post-inflationary vacuum strongly affects supersymmetric inflation. It is important to note the crucial difference between freezing of the modulus and actually stabilising it - the first approach misses parts of the scalar potential which turn out to be relevant for inflation. We argue, that it is more likely that the low scale supersymmetric inflation occurs at a critical point at the origin in the field space than at an inflection point away from the origin, as the necessary fine-tuning in the second case is typically larger.Comment: 10

Radiatively induced leptogenesis in a minimal seesaw model

We study the possibility that the baryon asymmetry of the universe is generated in a minimal seesaw scenario where two right-handed Majorana neutrinos with degenerate masses are added to the standard model particle content. In the usual framework of thermal leptogenesis, a nonzero $CP$ asymmetry can be obtained through the mass splitting induced by the running of the heavy Majorana neutrino masses from their degeneracy scale down to the seesaw scale. Although, in the light of the present neutrino oscillation data, the produced baryon asymmetry turns out to be smaller than the experimental value, the present mechanism could be viable in simple extensions of the standard model.Comment: 6 pages, 2 figures, uses RevTeX4, calculations improved, comments adde

Suppressing Proton Decay in the Minimal SO(10) Model

We show that in a class of minimal supersymmetric SO(10) models which have been found to be quite successful in predicting neutrino mixings, all proton decay modes can be suppressed by a particular choice of Yukawa textures. This suppression works for contributions from both left and right operators for nucleon decay and for arbitrary \tan\beta. The required texture not only fits all lepton and quark masses as well as CKM parameters but it also predicts neutrino mixing parameter U_e3 and Dirac CP phase \sin|\delta_MNS| to be 0.07-0.09 and 0.3-0.7 respectively. We also discuss the relation between the GUT symmetry breaking parameters for the origin of these textures.Comment: 7 pages, 2 figure

Collective treatment of High Energy Thresholds in SUSY - GUTs

Supersymmetric GUTs are the most natural extension of the Standard model unifying electroweak and strong forces. Despite their indubitable virtues, among these the gauge coupling unification and the quantization of the electric charge, one of their shortcomings is the large number of parameters used to describe the high energy thresholds (HET), which are hard to handle. We present a new method according to which the effects of the HET, in any GUT model, can be described by fewer parameters that are randomly produced from the original set of the parameters of the model. In this way, regions favoured by the experimental data are easier to locate, avoiding a detailed and time consuming exploration of the parameter space, which is multidimensional even in the most economic unifying schemes. To check the efficiency of this method, we directly apply it to a SUSY SO(10) GUT model in which the doublet-triplet splitting is realized through the Dimopoulos-Wilczek mechanism. We show that the demand of gauge coupling unification, in conjunction with precision data, locates regions of the parameter space in which values of the strong coupling \astrong are within the experimental limits, along with a suppressed nucleon decay, mediated by a higgsino driven dimension five operators, yielding lifetimes that are comfortably above the current experimental bounds. These regions open up for values of the SUSY breaking parameters m_0, M_1/2 < 1 TeV being therefore accessible to LHC.Comment: 21 pages, 8 figures, UA-NPPS/BSM-10/02 (added

Kahler potentials for the MSSM inflation and the spectral index

Recently it has been argued that some of the fine-tuning problems of the MSSM inflation associated with the existence of a saddle point along a flat direction may be solved naturally in a class of supergravity models. Here we extend the analysis and show that the constraints on the Kahler potentials in these models are considerably relaxed when the location of the saddle point is treated as a free variable. We also examine the effect of supergravity corrections on inflationary predictions and find that they can slightly alter the value of the spectral index. As an example, for flat direction field values $|\bar{\phi}_0|=1\times10^{-4}M_P$ we find $n\sim0.92 ... 0.94$ while the prediction of the MSSM inflation without any corrections is $n\sim0.92$.Comment: 13 pages, one figure. Typos corrected and a reference adde

Quintessential Kination and Leptogenesis

Thermal leptogenesis induced by the CP-violating decay of a right-handed neutrino (RHN) is discussed in the background of quintessential kination, i.e., in a cosmological model where the energy density of the early Universe is assumed to be dominated by the kinetic term of a quintessence field during some epoch of its evolution. This assumption may lead to very different observational consequences compared to the case of a standard cosmology where the energy density of the Universe is dominated by radiation. We show that, depending on the choice of the temperature T_r above which kination dominates over radiation, any situation between the strong and the super--weak wash--out regime are equally viable for leptogenesis, even with the RHN Yukawa coupling fixed to provide the observed atmospheric neutrino mass scale ~ 0.05 eV. For M< T_r < M/100, i.e., when kination stops to dominate at a time which is not much later than when leptogenesis takes place, the efficiency of the process, defined as the ratio between the produced lepton asymmetry and the amount of CP violation in the RHN decay, can be larger than in the standard scenario of radiation domination. This possibility is limited to the case when the neutrino mass scale is larger than about 0.01 eV. The super--weak wash--out regime is obtained for T_r << M/100, and includes the case when T_r is close to the nucleosynthesis temperature ~ 1 MeV. Irrespective of T_r, we always find a sufficient window above the electroweak temperature T ~ 100 GeV for the sphaleron transition to thermalize, so that the lepton asymmetry can always be converted to the observed baryon asymmetry.Comment: 13 pages, 8 figure

Detailed Analysis of Proton Decay Rate in the Minimal Supersymmetric SO(10) Model

We consider the minimal supersymmetric SO(10) model, where only one {\bf 10} and one $\bar{\bf 126}$ Higgs multiplets have Yukawa couplings with matter multiplets. This model has the high predictive power for the Yukawa coupling matrices consistent with the experimental data of the charged fermion mass matrices, and all the Yukawa coupling matrices are completely determined once a few parameters in the model are fixed. This feature is essential for definite predictions to the proton decay rate through the dimension five operators. We analyze the proton decay rate for the dominant decay modes $p \to K^{+} \bar{\nu}$ by including as many free parameters as possible and varying them. There are two free parameters in the Yukawa sector, while five in the Higgsino sector. It is found that an allowed region exists when the free parameters in the Higgs sector are tuned so as to cancel the proton decay amplitude. The resultant proton lifetime is proportional to $1/\tan^2 \beta$ and the allowed region eventually disappears as $\tan \beta$ becomes large.Comment: 15 pages, 3 figures; the version to appear in JHE

Charged Lepton Electric Dipole Moments from TeV Scale Right-handed Neutrinos

We study the connection between charged lepton electric dipole moments, $d_l$ $(l=e,\mu,\tau)$, and seesaw neutrino mass generation in a simple two Higgs doublet extension of the Standard Model plus three right-handed neutrinos (RHN) $N_a$, $a=1,2,3$. For RHN with hierarchical masses and at least one with mass in the 10 TeV range we obtain the upper bounds of $|d_e|< 9\times 10^{-30}$ e-cm and $|d_{\mu}|<2 \times 10^{-26}$ e-cm. Our scenario favors the normal mass hierarchy for the light neutrinos. We also calculated the cross section for e^-e^- \ra W^- W^- in a high luminosity collider with constraints from neutrinoless double beta decay of nuclei included. Among the rare muon decay experiments we find that \mu\ra e\gamma is most sensitive and the upper limit is $<8\times 10^{-13}$.Comment: references added, typos correcte

Astrophysical and Cosmological Implications of Large Volume String Compactifications

We study the spectrum, couplings and cosmological and astrophysical implications of the moduli fields for the class of Calabi-Yau IIB string compactifications for which moduli stabilisation leads to an exponentially large volume V ~ 10^{15} l_s^6 and an intermediate string scale m_s ~ 10^{11}GeV, with TeV-scale observable supersymmetry breaking. All K\"ahler moduli except for the overall volume are heavier than the susy breaking scale, with m ~ ln(M_P/m_{3/2}) m_{3/2} ~ (\ln(M_P/m_{3/2}))^2 m_{susy} ~ 500 TeV and, contrary to standard expectations, have matter couplings suppressed only by the string scale rather than the Planck scale. These decay to matter early in the history of the universe, with a reheat temperature T ~ 10^7 GeV, and are free from the cosmological moduli problem (CMP). The heavy moduli have a branching ratio to gravitino pairs of 10^{-30} and do not suffer from the gravitino overproduction problem. The overall volume modulus is a distinctive feature of these models and is an M_{planck}-coupled scalar of mass m ~ 1 MeV and subject to the CMP. A period of thermal inflation can help relax this problem. This field has a lifetime ~ 10^{24}s and can contribute to dark matter. It may be detected through its decays to 2\gamma or e^+e^-. If accessible the e^+e^- decay mode dominates, with Br(\chi \to 2 \gamma) suppressed by a factor (ln(M_P/m_{3/2}))^2. We consider the potential for detection of this field through different astrophysical sources and find that the observed gamma-ray background constrains \Omega_{\chi} <~ 10^{-4}. The decays of this field may generate the 511 keV emission line from the galactic centre observed by INTEGRAL/SPI.Comment: 31 pages, 2 figures; v2. refs adde