Long-lived particles at the energy frontier: the MATHUSLA physics case.

We examine the theoretical motivations for long-lived particle (LLP) signals at the LHC in a comprehensive survey of standard model (SM) extensions. LLPs are a common prediction of a wide range of theories that address unsolved fundamental mysteries such as naturalness, dark matter, baryogenesis and neutrino masses, and represent a natural and generic possibility for physics beyond the SM (BSM). In most cases the LLP lifetime can be treated as a free parameter from the [Formula: see text]m scale up to the Big Bang Nucleosynthesis limit of [Formula: see text] m. Neutral LLPs with lifetimes above [Formula: see text]100 m are particularly difficult to probe, as the sensitivity of the LHC main detectors is limited by challenging backgrounds, triggers, and small acceptances. MATHUSLA is a proposal for a minimally instrumented, large-volume surface detector near ATLAS or CMS. It would search for neutral LLPs produced in HL-LHC collisions by reconstructing displaced vertices (DVs) in a low-background environment, extending the sensitivity of the main detectors by orders of magnitude in the long-lifetime regime. We study the LLP physics opportunities afforded by a MATHUSLA-like detector at the HL-LHC, assuming backgrounds can be rejected as expected. We develop a model-independent approach to describe the sensitivity of MATHUSLA to BSM LLP signals, and compare it to DV and missing energy searches at ATLAS or CMS. We then explore the BSM motivations for LLPs in considerable detail, presenting a large number of new sensitivity studies. While our discussion is especially oriented towards the long-lifetime regime at MATHUSLA, this survey underlines the importance of a varied LLP search program at the LHC in general. By synthesizing these results into a general discussion of the top-down and bottom-up motivations for LLP searches, it is our aim to demonstrate the exceptional strength and breadth of the physics case for the construction of the MATHUSLA detector.

Constraining the Self-Interacting Neutrino Interpretation of the Hubble Tension.

Large, nonstandard neutrino self-interactions have been shown to resolve the ∼4σ tension in Hubble constant measurements and a milder tension in the amplitude of matter fluctuations. We demonstrate that interactions of the necessary size imply the existence of a force carrier with a large neutrino coupling (>10^{-4}) and mass in the keV-100 MeV range. This mediator is subject to stringent cosmological and laboratory bounds, and we find that nearly all realizations of such a particle are excluded by existing data unless it carries spin 0 and couples almost exclusively to τ-flavored neutrinos. Furthermore, we find that the light neutrinos must be Majorana particles, and that a UV-complete model requires a nonminimal mechanism to simultaneously generate neutrino masses and appreciable self-interactions.

Thermal Dark Matter Below a MeV.

We consider a class of models in which thermal dark matter is lighter than a MeV. If dark matter thermalizes with the standard model below the temperature of neutrino-photon decoupling, equilibration and freeze-out cool and heat the standard model bath comparably, alleviating constraints from measurements of the effective number of neutrino species. We demonstrate this mechanism in a model consisting of fermionic dark matter coupled to a light scalar mediator. Thermal dark matter can be as light as a few keV, while remaining compatible with existing cosmological and astrophysical observations. This framework motivates new experiments in the direct search for sub-MeV thermal dark matter and light force carriers.

Single-Center Experience of Surgical Treatment of Primary Retroperitoneal Tumors.

This study is an evaluation of surgical treatment results of primary retroperitoneal tumors. In Samara Regional Clinical Oncology Dispensary, from 2008 to 2015, the treatment of 187 patients (53 men and 134 women) was conducted. One hundred fifteen patients got tumor removal within the healthy tissue (R0), and 61 patients went through complete resection of tumor with wide margins (R0). Complete resection of tumor with wide margins (R0) with preoperative tumor vessel embolization was performed in 11 patients. According to the histological examination, malignant retroperitoneal tumor was detected in 85 patients (48.4%); in most cases it was presented by various forms of sarcoma. A benign tumor was diagnosed in 71 patients (40.3%), fibrolipomas (17.1%), and neurofibromas (12.5%). The diagnosis of 20 patients needs subsequent clarification, as mesenchymal tumor (6.2%) and histiocytoma (5.1%) were diagnosed. Short-term results of surgical treatment for the group, where complete resection of tumor with wide margins was performed: intraoperative blood loss 410.91 + - 113.31(ml), operation time 185.15 + -32.49(min); postoperative complications 10 (16,4%); mortality 3 (4,9%); LOS 23,14 ± 6,31; for removal of the tumor within healthy tissues: intraoperative blood loss 281.33 + -110.94 (ml), operation time 58.33 + -27.14(min) postoperative complications 7 (6,08%); mortality 2 (1,74%); LOS 6,98 ± 4,83; (t = 279, p = 0,015). For patients who went through preoperative tumor feeding vessel embolization, intraoperative blood loss was 121.33 ± 27.94 (ml), time of operation 43.13 ± 16.11 (min), postoperative complication 1 (4.5%), mortality 0 (0%), and length of stay 12.72 ± 1.49. After the complete resection of tumor with wide margins, intraoperative blood loss, operation time, the number of postoperative complications, and postoperative LOS were significantly greater in comparison with the group of patients where the tumor was removed within healthy tissues. The method of preoperative embolization of the tumor feeding vessels can reduce intraoperative blood loss, the time of operation, and the number of postoperative complications.

The Results of the Combine Treatment of Patients with Liver Bilobar Metastases from Colorectal Cancer Using Radiofrequency Ablation.

Colorectal cancer (CRC) is the third most common cancer worldwide. The mortality from CRC remains very high. The main cause of such a high mortality is a disseminate process with the appearance of distant metastases. In this regard, the treatment of metastatic lesions is recognized as an important trend in modern oncology. The program of study included 176 patients with colorectal cancer after primary tumor removal with the malignant progression-multiple (more than 4) bilobar liver metastases. The research was organized in Samara Regional Oncology Centre from 2001 to 2014. By the treatment method, patients were divided into two groups. Main group got the combined (chemotherapy + radiofrequency ablation (RFA)) treatment (n = 98). In control group, only chemotherapy was applied (n = 78). One-, two-, and three-year OS were 73.5, 25.1, and 7.2% in the main group and 39.6, 6.3, and 2.1% in the control group. The RFA application allowed us to reach the index of 4-year survival 1.8% in the main group, while we received only 2.1 of 3-year survival in the control group. The OS median reached 18 months in the main group and 11 months in the control group. So, the OS curves in two comparing groups were significantly different according to statistics (log-rank test 3.77, р = 0.000). The application of RFA in combination with chemotherapy in the treatment of bilobar metastasis colorectal cancer allows to improve the performance of disease-free survival and overall survival significantly, compared with the group of patients who received only chemotherapy.