55263386
Higgs Mass Prediction for Realistic String/M Theory Vacua
Recently it has been recognized that in compactified $\mathrm{\text{string}}/M$ theories that satisfy cosmological constraints, it is possible to derive some robust and generic predictions for particle physics and cosmology with very mild assumptions. When the matter and gauge content below the compactification scale is that of the minimal supersymmetric standard model (MSSM), it is possible to make precise predictions. In this case, we predict that there will be a single standard model-like Higgs boson with a calculable mass $105\text{ }\text{ }\mathrm{GeV}\ensuremath{\lesssim}{M}_{h}\ensuremath{\lesssim}129\text{ }\text{ }\mathrm{GeV}$ depending on $\mathrm{tan}﻿\ensuremath{\beta}$ (the ratio of the Higgs vevs in the MSSM). For $\mathrm{tan}﻿\ensuremath{\beta}g7$, the prediction is $122\text{ }\text{ }\mathrm{GeV}\ensuremath{\lesssim}{M}_{h}\ensuremath{\lesssim}129\text{ }\text{ }\mathrm{GeV}$.
118825124
Neutrino masses, Baryon asymmetry, dark matter and the moduli problem ? A complete framework
Recent developments in string theory have led to ``realistic string compactifications which lead to moduli stabilization while generating a hierarchy between the Electroweak and Planck scales at the same time. However, this seems to suggest a rethink of our standard notions of cosmological evolution after the end of inflation and before the beginning of BBN. This epoch is crucial for addressing the issues of neutrino masses, baryon asymmetry, Dark Matter (DM) abundance and the moduli (gravitino) problem. We argue that within classes of realistic string compactifications as defined above, there generically exists a light modulus with a mass comparable to that of the gravitino which is typically much smaller than the Hubble parameter during inflation. Therefore, it is destabilized and generates a large late-time entropy when it decays. Thus, all known elegant mechanisms of generating the baryon asymmetry of the Universe in the literature have to take this fact into account. In this work, we find that it is still possible to naturally generate the observed baryon asymmetry of the Universe as well as light left-handed neutrino masses from a period of Affleck-Dine (AD) leptogenesis shortly after the end of inflation, in classes of realistic string constructions with a minimal extension of the MSSM below the unification scale (consisting only of right-handed neutrinos) and satisfying certain microscopic criteria described in the text. The AD mechanism has already been used to generate the baryon asymmetry in the literature; however in this work we have embedded the above mechanism within a framework well motivated from string theory and have tried to describe the epoch from the end of inflation to the beginning of BBN in a complete and self-consistent manner. The consequences of our analysis are as follows. The lightest left-handed neutrino is required to be virtually massless. The moduli (gravitino) problem can be naturally solved in this framework both within gravity and gauge mediation. The observed upper bound on the relic abundance constrains the moduli-matter and moduli-gravitino couplings since the DM is produced non-thermally within this framework. Finally, although not a definite prediction, the framework naturally allows a light right-handed neutrino and sneutrinos around the electroweak scale which could have important implications for the nature of DM as well as the LHC.
123633440
Oblique electroweak parameters S and T for superconformal field theories
53143827
OPE methods for the holomorphic Higgs portal
A bstractWe develop a systematic and general approach to study the effective Higgs Lagrangian in a supersymmetric framework in which the Higgs fields in the visible sector couple weakly to another sector. The extra sector may be strongly coupled in general. It is assumed to be superconformal in the ultraviolet, but develop a mass-gap with supersymmetry breaking in the infrared. The main technique used in our approach is that of the operator product expansion (OPE). By using OPE methods we are able to compute the parameters in the Higgs Lagrangian to quadratic order and make general statements that are applicable to many classes of models. Not only does this approach allow us to understand the traditional problems plaguing simple models from a different perspective, it also reveals new possibilities for solutions of these problems. The methods and results of our work should be useful in constructing a viable and natural model of physics beyond the Standard Model.
5529024
Visible sector supersymmetry breaking revisited
We revisit the possibility of ``visible sector'' SUSY models: models which are straightforward renormalizable extensions of the Minimal Supersymmetric Standard Model (MSSM), where SUSY is broken at tree level. Models of this type were abandoned twenty years ago due to phenomenological problems, which we review. We then demonstrate that it is possible to construct simple phenomenologically viable visible sector SUSY models. Such models are indeed quite constrained, and have some inelegant features. They also have interesting and distinctive phenomenology. Our models predict light gauginos and very heavy squarks and sleptons. The squarks and sleptons may not be observable at the LHC. The LSP is a stable very light gravitino with a significant Higgsino admixture. The NLSP is mostly Bino. The Higgs boson is naturally heavy. Proton decay is sufficently and naturally suppressed, even for a cutoff scale as low as 108 GeV. The lightest particle of the O'Raifeartaigh sector (the LOP) is stable, and is an interesting cold dark matter candidate.
199635013
Connecting String/M Theory to the Electroweak Scale and to LHC Data
The Standard Model of particle physics explains (almost) all observed non-gravitational microscopic phenomena but has many open theoretical questions. We are on the threshold of unraveling the mysteries of the Standard Model and discovering its extension. This could be achieved in the near future with the help of many experiments in particle physics and cosmology, the LHC in particular. Assuming that data confirming the existence of new physics beyond the Standard Model is obtained, one is left with the very important and challenging task of solving the "Inverse Problem", \emph{viz.} "How can one deduce the nature of the underlying (perhaps microscopic) theory from data?" This thesis explores this question in detail, and also proposes an approach to address the problem in a meaningful way which could prove crucial to the possible solution to this problem in the future. The proposed approach has three aspects - a) To systematically study classes of microscopic (string/$M$ theory) constructions to the extent that they could be connected to low energy physics (electroweak scale), b) To find patterns of experimental observables which are sensitive to the properties of the underlying theoretical constructions thereby allowing us to distinguish among different constructions, and c) To try to get insights about the qualitative features of the theoretical model from data in a bottom-up approach which complements the top-down approach and strengthens it as well. This thesis studies all the above aspects in detail. The methods used and results obtained in this thesis will hopefully be of great importance in solving the Inverse Problem.
1102417
Properties of Gamma-Ray Burst Progenitor Stars
We determined some basic properties of stars that produce spectacular gamma-ray bursts at the end of their lives. We assumed that accretion of the outer portion of the stellar core by a central black hole fuels the prompt emission and that fall-back and accretion of the stellar envelope later produce the plateau in the x-ray light curve seen in some bursts. Using x-ray data for three bursts, we estimated the radius of the stellar core to be ∼(1 – 3) × 1010 cm and that of the stellar envelope to be ∼(1 – 2) × 1011 cm. The density profile in the envelope is fairly shallow, with ρ ∼ r–2 (where ρ is density and r is distance from the center of the explosion). The rotation speeds of the core and envelope are ∼0.05 and ∼0.2 of the local Keplerian speed, respectively.
14397467
A unified picture for gamma‐ray burst prompt and X‐ray afterglow emissions
Also available at http://www.blackwell-synergy.com/doi/abs/10.1111/j.1745-3933.2006.00138.x. The definitive version is available at www.blackwell-synergy.com.
15553917
Model-dependent high-energy neutrino flux from gamma-ray bursts.
The IceCube Collaboration recently reported a stringent upper limit on the high energy neutrino flux from gamma-ray bursts (GRBs), which provides a meaningful constraint on the standard internal shock model. Recent broadband electromagnetic observations of GRBs also challenge the internal shock paradigm for GRBs, and some competing models for γ-ray prompt emission have been proposed. We describe a general scheme for calculating the GRB neutrino flux, and compare the predicted neutrino flux levels for different models. We point out that the current neutrino flux upper limit starts to constrain the standard internal shock model. The dissipative photosphere models are also challenged if the cosmic ray luminosity from GRBs is at least 10 times larger than the γ-ray luminosity. If the neutrino flux upper limit continues to go down in the next few years, then it would suggest the following possibilities: (i) the photon-to-proton luminosity ratio in GRBs is anomalously high for shocks, which may be achieved in some dissipative photosphere models and magnetic dissipation models; or (ii) the GRB emission site is at a larger radius than the internal shock radius, as expected in some magnetic dissipation models such as the internal collision-induced magnetic reconnection and turbulence model.
53358770
Evidence for mild deviation from power-law distribution of electrons in relativistic shocks: GRB 090902B
Many previous studies have determined that the long lasting emission at X-ray, optical and radio wavelengths from gamma-ray bursts (GRBs), called the afterglow, is likely produced by the external forward shock model. In this model, the GRB jet interacts with the circum-stellar medium and drives a shock that heats the medium, which radiates via synchrotron emission. In this work, we carried out a detailed analysis of the late time afterglow data of GRB 090902B using a very careful accounting of the Inverse Compton losses. We find that in the context of the external forward shock model, the only viable option to explain the X-ray and optical data of GRB 090920B is to have the electron energy distribution deviate from a power-law shape and exhibit some slight curvature immediately downstream of the shock front (we explored other models that rely on a single power-law assumption, but they all fail to explain the observations). We find the fraction of the energy of shocked plasma in magnetic field to be ∼10 −6 using late time afterglow data, which is consistent with the value obtained using early gamma-ray data. Studies like the present one might be able to provide a link between GRB afterglow modelling and numerical simulations of particle acceleration in collisionless shocks. We also provide detailed calculations for the early (10 3 s) high-energy (>100 MeV) emission and confirm that it is consistent with origin in the external forward shock. We investigated the possibility that the ∼10 keV excess observed in the spectrum during the prompt phase also has its origin in the external shock and found the answer to be negative.
18521155
H I observations of two molecular clouds with extremely large velocity dispersions
We have mapped two molecular clouds at (i, b) = (3.2°, + 0.3°) and (i, b) = (5.4°, - OS) in 21-cm line and continuum emission. These clouds show unusually large velocity dispersions of more than 100 km s -1 (FWHM) which has also been seen in 12CO, 13CO and CS emissions. This dispersion is approximately an order of magnitude larger compared with giant molecular clouds. From our H I observations we estimate that the atomic mass of the cloud at i = 3.2° is about 1.5 x 105 Mo and the mass of the cloud at i = 5.4° is 7 x 104 Mo. The ratio of total molecular mass to atomic mass for these clouds appears to be normal for clouds near the Galactic Centre. The main peculiar feature of these clouds is their abnormally large velocity dispersion; the extent in velocity is from about 0 [local standard of rest (LSR)] to 200 km S-I. These clouds are connected, in the i-v plane, to high-velocity ridges that extend over several degrees of longitude. These properties, we believe, provide important clues to the physical process responsible for their large velocity dispersion.