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.
119028722
Origins of hidden sector dark matter I: cosmology
We present a systematic cosmological study of a universe in which the visible sector is coupled, albeit very weakly, to a hidden sector comprised of its own set of particles and interactions. Assuming that dark matter (DM) resides in the hidden sector and is charged under a stabilizing symmetry shared by both sectors, we determine all possible origins of weak-scale DM allowed within this broad framework. We show that DM can arise only through a handful of mechanisms, lending particular focus to Freeze-Out and Decay and Freeze-In, as well as their variations involving late time re-annihilations of DM and DM particle anti-particle asymmetries. Much like standard Freeze-Out, where the abundance of DM depends only on the annihilation cross-section of the DM particle, these mechanisms depend only on a very small subset of physical parameters, many of which may be measured directly at the LHC. In particular, we show that each DM production mechanism is associated with a distinctive window in lifetimes and cross-sections for particles which may be produced in the near future. We evaluate prospects for employing the LHC to definitively reconstruct the origin of DM in a companion paper.
119200117
The Higgs as a probe of supersymmetric extra sectors
A bstractWe present a general method for calculating the leading contributions to h0 → gg and h0 → γγ in models where the Higgs weakly mixes with a nearly supersymmetric extra sector. Such mixing terms can play an important role in raising the Higgs mass relative to the value expected in the MSSM. Our method applies even when the extra sector is strongly coupled, and moreover does not require a microscopic Lagrangian description. Using constraints from holomorphy we fix the leading parametric form of the contributions to these Higgs processes, including the Higgs mixing angle dependence, up to an overall coefficient. Moreover, when the Higgs is the sole source of mass for a superconformal sector, we show that even this coefficient is often calculable. For appropriate mixing angles, the contribution of the extra states to h0 → gg and h0 → γγ can vanish. We also discuss how current experimental limits already lead to non-trivial constraints on such models. Finally, we provide examples of extra sectors which satisfy the requirements necessary to use the holomorphic approximation.
55061398
LHC string phenomenology
We argue that it is possible to address the deeper LHC inverse problem, to gain insight into the underlying theory from LHC signatures of new physics. We propose a technique which may allow us to distinguish among, and favor or disfavor, various classes of underlying theoretical constructions using (assumed) new physics signals at the LHC. We think that this can be done with limited data (5–10 fb−1), and improved with more data. This is because of two reasons: (a) it is possible in many cases to reliably go from (semi)realistic microscopic string constructions to the space of experimental observables, say, LHC signatures, and (b) the patterns of signatures at the LHC are sensitive to the structure of the underlying theoretical constructions. We illustrate our approach by analyzing two promising classes of string compactifications along with six other string-motivated constructions. Even though these constructions are not complete, they illustrate the point we want to emphasize. We think that using this technique effectively over time can eventually help us to meaningfully connect experimental data to microscopic theory.
118571038
Unravelling strings at the CERN LHC
We construct LHC signature footprints for four semirealistic string/M theory vacua with a minimal supersymmetric standard model visible sector. We find that they all give rise to limited regions in LHC signature space and are qualitatively different from each other for understandable reasons. We also propose a technique in which correlations of LHC signatures can be effectively used to distinguish among these string theory vacua. We expect the technique to be useful for more general string vacua. We argue that further systematic analysis with this approach will allow LHC data to disfavor or exclude major 'corners' of string/M theory and favor others. The technique can be used with limited integrated luminosity and improved.
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.
389277
Mass Fall-back and Accretion in the Central Engine of Gamma-Ray Bursts
We calculate the rate of in-fall of stellar matter on an accretion disc during the collapse of a rapidly rotating massive star and estimate the luminosity of the relativistic jet that results from accretion on to the central black hole. We find that the jet luminosity remains high for about 102 s, at a level comparable to the typical luminosity observed in gamma-ray bursts (GRBs). The luminosity then decreases rapidly with time for about ∼103 s, roughly as ∼t−3; the duration depends on the size and rotation speed of the stellar core. The rapid decrease of the jet power explains the steeply declining X-ray flux observed at the end of most long-duration GRBs. 
 
 
 
Observations with the Swift satellite show that, following the steep decline, many GRBs exhibit a plateau in the X-ray light curve (XLC) that lasts for about 104 s. We suggest that this puzzling feature is due to continued accretion in the central engine. A plateau in the jet luminosity can arise when the viscosity parameter α is small, ∼10−2 or less. A plateau is also produced by continued fall-back of matter – either from an extended stellar envelope or from material that failed to escape with the supernova ejecta. In a few GRBs, the XLC is observed to drop suddenly at the end of the plateau phase, while in others the XLC declines more slowly as ∼t−1−t−2. These features arise naturally in the accretion model depending on the radius and mean specific angular momentum of the stellar envelope. 
 
 
 
The total energy in the disc-wind accompanying accretion is found to be about 1052 erg. This is comparable to the energy observed in supernovae associated with GRBs, suggesting that the wind might be the primary agent responsible for the explosion. 
 
 
 
The accretion model thus provides a coherent explanation for the diverse and puzzling features observed in the early XLC of GRBs. It might be possible to use this model to invert gamma-ray and X-ray observations of GRBs and thereby infer basic properties of the core and envelope of the GRB progenitor star.
118788230
GEODESIC FLOWS AND THEIR DEFORMATIONS IN BERTRAND SPACETIMES
In this article we will discuss some features of a particular spacetime called Bertrand space-time of Type II (BST-II). The talk discusses about the energy conditions and the ESR parameters in this spacetime.
8395650
Energetics and Luminosity Function of Gamma-Ray Bursts
Gamma-ray bursts (GRBs) are believed to be some catastrophic event in which material is ejected at a relativistic velocity, and internal collisions within this ejecta produce the observed γ-ray flash. The angular size of a causally connected region within a relativistic flow is of the order the angular width of the relativistic beaming, γ-1. Thus, different observers along different lines of sight could see drastically different fluxes from the same burst. Specifically, we propose that the most energetic bursts correspond to exceptionally bright spots along the line of sight on colliding shells and do not represent much larger energy release in the explosion. The energy budget for an average GRB in this model is, however, same as in the uniform shell model. We calculate the distribution function of the observed fluence for random angular-fluctuation of ejecta. We find that the width of the distribution function for the observed fluence is about 2 orders of magnitude if the number of shells ejected along different lines of sight is 10 or less. The distribution function becomes narrower if number of shells along typical lines of sight increases. The analysis of the γ-ray fluence and afterglow emissions for GRBs with known redshifts provides support for our model, i.e., the large width of GRB luminosity function is not due to a large spread in the energy release but instead is due to large angular fluctuations in ejected material. We outline several observational tests of this model. In particular, for δ-function energy distribution in explosions we predict little correlation between the γ-ray fluence and the afterglow emission as in fact is observed. We predict that the early (minutes-to-hours) afterglow would depict large temporal fluctuations whose amplitude decreases with time. Finally, we predict that there should be many weak bursts with about average afterglow luminosity in this scenario.
119369890
Off-Axis Afterglow Emission from Jetted Gamma-Ray Bursts
We calculate gamma-ray burst (GRB) afterglow light curves from a relativistic jet as seen by observers at various viewing angles, θobs, relative to the jet axis. We describe three increasingly more realistic models and compare the resulting light curves. An observer at θobs θ0 sees a rising light curve at early times, peaking when the jet Lorentz factor is ~1/θobs, and approaching that seen by an on-axis observer, at later times. A strong linear polarization (40%) may occur near the peak in the light curve and slowly decay with time. We show that, if GRB jets have a universal energy, then orphan afterglows are detectable up to a maximum offset angle that is independent of the jet initial aperture and thus at a rate proportional to the true GRB rate. We also discuss the implications of the proposed connection between SN 1998bw and GRB 980425.
16795402
Dissipation of a Tide in a Differentially Rotating Star
The orbital period of the binary pulsar PSR J0045-7319, which is located in our neighboring galaxy, the Small Magellanic Cloud (SMC), appears to be decreasing on a timescale of ~5 × 105 yr. This timescale is more than 2 orders of magnitude smaller than what is expected from the standard theory of tidal dissipation. Kumar & Quataert proposed that this rapid evolution could be understood provided that the neutron star's companion, a main-sequence B star, has set up significant differential rotation. The goal of this paper is to evaluate the redistribution of angular momentum in the B star due to meridional circulation and shear stresses and to calculate the evolution of the rotation profile when these two processes act in competition with the deposition of momentum by the tidal wave. We find that although angular momentum redistribution is important, the B star may continue to have sufficient differential rotation so that tidal waves are entirely absorbed as they arrive at the surface. The mechanism proposed by Kumar & Quataert to speed up the orbital evolution of the SMC binary pulsar should therefore work as suggested.