119290042
Origins of hidden sector dark matter II: collider physics
We consider a broad class of supersymmetric theories in which dark matter (DM) is the lightest superpartner (LSP) of a hidden sector that couples very weakly to visible sector fields. Portal interactions connecting visible and hidden sectors mediate the decay of the lightest observable superpartner (LOSP) into the LSP, allowing the LHC to function as a spectacular probe of the origin of hidden sector DM. As shown in a companion paper, this general two-sector framework allows only for a handful of DM production mechanisms, each of which maps to a distinctive window in lifetimes and cross-sections for the LOSP. In the present work we perform a systematic collider study of LOSP candidates and portal interactions, and for each case evaluate the prospects for successfully reconstructing the origin of DM at the LHC. If, for instance, DM arises from Freeze-Out and Decay, this may be verified if the LOSP is a bino or right-handed slepton decaying to the LSP through a variety of portal interactions, and with an annihilation cross-section within a narrow range. On the other hand, the Freeze-In mechanism may be verified for a complimentary set of LOSP candidates, and within a narrow range of LOSP lifetimes. In all cases, the LOSP is relatively long-lived on collider time scales, leading to events with displaced vertices. Furthermore, scenarios with a charged or colored LOSP are particularly promising.
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.
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.
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.
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.
10083588
Gamma-Ray Burst Energetics
We estimate the fraction of the total energy in a gamma-ray burst (GRB) that is radiated in photons during the main burst. Random internal collisions among different shells limit the efficiency for converting bulk kinetic energy to photons. About 1% of the energy of explosion is converted to radiation, in the 10-103 keV energy band in the observer frame, for long-duration bursts (lasting 10 s or more); the efficiency is significantly smaller for shorter duration bursts. Moreover, about 50% of the energy of the initial explosion could be lost to neutrinos during the early phase of the burst if the initial fireball temperature is ~10 MeV. If isotropic, the total energy budget of the brightest GRBs is 1055 ergs, a factor of 20 larger than previously estimated. Anisotropy of explosion, as evidenced in two GRBs, could reduce the energy requirement by a factor of 10-100. Putting these two effects together, we find that the energy release in the most energetic bursts is about 1054 ergs.
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.
53636345
MAGNETIC FIELDS IN RELATIVISTIC COLLISIONLESS SHOCKS
We present a systematic study on magnetic fields in gamma-ray burst (GRB) external forward shocks (FSs). There are 60 (35) GRBs in our X-ray (optical) sample, mostly from Swift. We use two methods to study B (fraction of energy in magnetic field in the FS): (1) for the X-ray sample, we use the constraint that the observed flux at the end of the steep decline is ≥ X-ray FS flux; (2) for the optical sample, we use the condition that the observed flux arises from the FS (optical sample light curves decline as ~t –1, as expected for the FS). Making a reasonable assumption on E (jet isotropic equivalent kinetic energy), we converted these conditions into an upper limit (measurement) on B n 2/(p + 1) for our X-ray (optical) sample, where n is the circumburst density and p is the electron index. Taking n = 1 cm–3, the distribution of B measurements (upper limits) for our optical (X-ray) sample has a range of ~10–8-10–3 (~10–6-10–3) and median of ~few × 10–5 (~few × 10–5). To characterize how much amplification is needed, beyond shock compression of a seed magnetic field ~10 μG, we expressed our results in terms of an amplification factor, AF, which is very weakly dependent on n (AF∝n 0.21). The range of AF measurements (upper limits) for our optical (X-ray) sample is ~1-1000 (~10-300) with a median of ~50 (~50). These results suggest that some amplification, in addition to shock compression, is needed to explain the afterglow observations.
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.
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.